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Vasodilating effect of benidipine hydrochloride in the renal and hindquarter vascular regions (supplied by terminal aorta) of spontaneously hypertensive rats
General Pharmacology 33 (1999) 127–136
Vasodilating effect of benidipine hydrochloride in the renal and hindquarter vascular regions (supplied by terminal aorta) of spontaneously hypertensive rats Yasuhiro Teranishia,*, Ryoji Ozonob, Atsunori Yoshimizuc, Atsushi Uedac, Satoshi Kurisuc, Hiromichi Tsurud a Department of Physiology, Hiroshima University, School of Medicine, Minami-ku, Hiroshima 734-8551, Japan Department of Clinical Laboratory Medicine, Hiroshima University, School of Medicine, Minami-ku, Hiroshima 734-8551, Japan c First Department of Internal Medicine, Hiroshima University, School of Medicine, Minami-ku, Hiroshima 734-8551, Japan d Department of Pharmacology, Toho University School of Medicine, Ohta-ku, Tokyo 143-8540, Japan Received 12 August 1998; accepted 21 December 1998
b
Abstract One of two Ca antagonists, benidipine (3–30 mg/kg) or nifedipine (30–600 g/kg), was administered in a bolus injection through the jugular vein, and the changes in mean arterial pressure (MAP), renal flow (RF), and hindquarter flow (HQF) in conscious spontaneously hypertensive rats (SHRs) and normotensive control rats (NCRs). Renal vascular resistance (RR) and hindquarter resistance (HQR) were calculated as MAP divided by RF and HQF, respectively. When a high dose was administered to decrease the blood pressure by about 20%, the RR was significantly lower with benidipine than with nifedipine. The decrease in HQR was not significantly different between benidipine and nifedipine. When a low dose was administered to decrease the blood pressure by about 7%, the decrease in RR was not significantly different between benidipine and nifedipine, but the HQR was significantly lower with benidipine than with nifedipine. In the NCRs, no pharmacological properties were significantly different between these two Ca antagonists. 1999 Elsevier Science Inc. All rights reserved. Keywords: Benidipine; Calcium antagonist; Renal resistance; Hindquarter resistance; Skeletal muscle vascular resistance; SHR
In patients with essential hypertension as well as animals with experimental hypertension, regional vascular flow and vascular resistance are not homogenous. In addition, the effects of antihypertensive drugs, including calcium antagonists, are not the same in the treatment of essential hypertension. Among these drugs, benidipine hydrochloride is a dihydropyridine (DHP) calcium antagonist that is thought to exert its effect by inhibiting the slow inward calcium ion current in smooth muscle cells (Terada et al., 1987). The antihypertensive effects of benidipine in dogs (Karasawa et al., 1988a, 1988b), cats (Karasawa et al., 1988c), rats (Karasawa et al., 1988d, 1988e), and humans (Shimamoto and Shimamoto, 1997) are long-acting and have a slow onset compared with other calcium antagonists. In conscious spontaneously hypertensive rats (SHRs), benidipine has been observed to have long-acting antihypertensive * Corresponding author. Tel.: 181-82-257-5126; fax: 181-82-2575187. E-mail address: [email protected] (Y. Teranishi)
effects of increasing cardiac output and decreasing total peripheral vascular resistance (TPR). In particular, benidipine vasodilating effect in the cardiac (coronary artery) and renal regions has been reported to be remarkable (Harashima et al., 1994), and it also showed a vasodilating effect in most regional vascular regions but had no effect on skeletal muscle (Harashima et al., 1994). Similar peripheral vasodilation was produced by another calcium antagonist, nitrendipine (Clozel, 1988). However, in our early studies, we observed that the vasodilating effect of benidipine was more marked than that of nifedipine in the hindquarter (HQ) vascular region (most of it is thought to cover vessels of the lower extremity muscle) of unanesthetized and unrestrained SHRs, while in the renal vascular region, there was no significant difference between the two Ca antagonists in vasodilating effects. However, it has recently been reported that benidipine has a specific vasodilating effect on the renal vascular region, which other Ca antagonists do not have (Kenjirou, 1994). To explore these contradictions, we observed the an-
0306-3623/99/$ – see front matter 1999 Elsevier Science Inc. All rights reserved. PII: S0306-3623(99)00003-8
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tihypertensive effects of benidipine and nifedipine at wide-ranging doses and chose the doses and times at which the antihypertensive effect and heart rate were changed to the same extent. We then compared the renal vasodilating effect and the HQ vascular vasodilating effect of benidipine with those of nifedipine measured simultaneously. Among the many Ca antagonists, Ca antagonists that improve renal blood flow and prevent the induction of renal failure are generally believed to be the best, while it is the skeletal muscles that are a key vascular region contributing to the maintenance of hypertension in SHRs because a marked elevation of skeletal muscle vascular resistance contributes to the increase in the TPR of SHRs (Iriuchijima, 1985, 1986, 1988), and because hypertension of SHRs is maintained by an increase in the TPR (Ferario and Page, 1978; Iriuchijima and Teranishi, 1982; Smith and Hutchins, 1979). Hence, the skeletal muscle is also an important vascular region that should be improved.
was observed for 20 to 30 min in its home cage. Then, the SHRs were treated with benidipine (3–30 mg/kg) or nifedipine (30–600 mg/kg) in a bolus i.v. injection, and arterial pressure, heart rate, and respective local blood flows were measured every 10 min for 30 min. Renal and HQ vascular resistances were calculated by dividing the arterial pressure by the simultaneously measured local blood flow. The NCRs were treated with benidipine (10 or 30 mg/kg) or nifedipine (100 or 600 mg/ kg) by i.v. injection, and similar measurements were performed. The arterial pressure values were smoothed with a resistance and capacitance (RC) filter with a time constant of 1 s and recorded by a pen writer. Each flow probe was calibrated before implantation by passing known amounts of saline through the excised artery. Flow signals were integrated with a time constant of 1 s to obtain the mean flow. The blood flow and local vascular resistance data were normalized to values per 100 g of body weight for comparison. 1.3. Drugs used
1. Materials and methods 1.1. Experimental animals and operation Male SHRs and normotensive control Wistar rats (NCRs) at 14–16 weeks of age were anesthetized with 50 mg/kg of thiamylal sodium by intraperitoneal injection, and either the right renal artery or the terminal abdominal aorta (most of the blood flow measured there is considered to be that of the lower-extremity muscles) was equipped with the probe (1.0- and 2.0-mm inside diameters, respectively) of an electromagnetic flowmeter (Nihon Kohden Co., Tokyo). At the same time, a cannula (PE-50) for arterial pressure measurement was inserted from the right common carotid artery to near the aortic arch. Another cannula (PE-10 fused to PE-20) for the i.v. injection of the calcium antagonist was inserted into the right jugular vein. The opposite end of each tube was exteriorized at the neck. The SHRs and Wistar rats were purchased from Charles River Japan Inc. (Yokohama, Japan). 1.2. Measurements of arterial pressure, heart rate, and local blood flow After the instrumentation operation described above, the rats were housed separately in plastic cages that measured 35 3 30 3 17 (depth) cm and were lined with wood chips. The rats were allowed ad libitum food pellets and drinking water. Three days after fixation of the electromagnetic flowmeter probe and cannulation, the rats’ arterial pressure, heart rate, and blood flow of the renal artery or terminal abdominal aorta (hereafter referred to as the hindquarter [HQ]) were measured simultaneously. First, to examine hemodynamics at the resting stage, each rat was allowed to freely behave and
Thiamylal sodium (Isozol, Yoshitomi Pharmaceuticals, Osaka, Japan) was used in the present study. Benidipine and nifedipine were gifts from Kyowa Hakko Kogyo Co. (Tokyo, Japan). Each Ca antagonist was kneaded well with a drop of polyoxyethylene (20) sorbitan monooleate in a mortar and then diluted with isotonic sodium chloride solution to adjust the concentration to 1000 mg/ml. 1.4. Statistical analysis All values are expressed as mean 6 SD. One-way analysis of variance (ANOVA) followed by Dunnett’s test was used to examine the changes after the administration of the two calcium antagonists (differences from pre-dose data). The statistical analysis was performed with the unpaired t test to determine the significance of the differences between the renal group and the HQ group treated with the same drug, at the same dose, and at the same time point, and also the differences between benidipine and nifedipine effects in the same artery group. The significance level was set at p , 0.05.
2. Results 2.1. Comparison of each parameter at the resting stage (before the administration of a calcium antagonist) between SHRs and NCRs Mean arterial pressure (MAP), renal and HQ blood flows, and renal and HQ vascular resistances at the resting stage were compared between SHRs and NCRs (Table 1). In the SHRs, MAP was significantly higher (p , 0.001), the renal flow was not changed, the HQ flow was significantly decreased (p , 0.001), and the re-
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Table 1 Mean arterial pressure (MAP), renal flow (RF), hindquarter flow (HQF), renal resistance (RR), and hindquarter resistance (HQR) at the resting stage before drug administration in spontaneously hypertensive rats (SHR) and normotensive control rats (NCR) Group
n
MAP
RF
HQF
RR
HQR
SHR Renal SHR Hindq Total
49
157 6 144
1.97 6 0.47
—
84.4 6 22.7*
—
44
156 6 14.7
—
3.42 6 0.84*
—
48.2 6 12.2*
93
157 6 14.5*
23
116 6 8.38
2.07 6 0.50
—
59.9 6 16.9
—
29
113 6 10.5
—
4.46 6 1.02
—
26.3 6 5.23
52
114 6 9.68
NCR Renal NCR Hindq Total
Each value is the mean 6 SD of n rats. * Each difference between SHR and NCR was significant at p , 0.001.
nal and HQ vascular resistances were significantly increased (p , 0.001). 2.2. Effects of benidipine and nifedipine on the renal and HQ vascular regions of the SHRs After the administration of benidipine, MAP was significantly decreased in a dose-dependent manner, and this antihypertensive effect lasted for at least 30 min (Fig. 1, top left). Renal vascular resistance (RR), calculated by MAP/renal blood flow (RF), also showed a similar dose-dependent decrease, which lasted up to 30 min (Fig. 2, top left). The HQ resistance was significantly decreased up to 30 min after the administration of high-dose benidipine (30 mg/kg) (Fig. 2, bottom left). In contrast, after the administration of nifedipine, MAP was transiently decreased at 10 min, but increased thereafter and returned to the pre-dose level at 30 min (Fig. 1, top right). Renal resistance was significantly decreased at and after 10 min, at only two doses (30 mg/ kg and 600 mg/kg), and it was significantly decreased up to 30 min after the administration of nifedipine at doses of 30, 100, and 600 mg/kg; however, at the dose of 300 mg/kg, it was transiently decreased at 10 min but increased thereafter to the pre-dose level (Fig. 2, top right). HQ resistance underwent no significant change after the administration of nifedipine at doses of 30, 100, and 300 mg/kg, but it was significantly decreased up to 30 min after the administration of the highest dose (600 mg/kg) (Fig. 2, bottom right). Both benidipine and nifedipine significantly increased heart rate at and after 20 min (Fig. 1, bottom). 2.3. Comparison of local vasodilating effects between benidipine and nifedipine Since the antihypertensive effects of benidipine and nifedipine differed in extent and time course, a local vasodilating effect was compared at the dose and time at which each drug produced almost the same extent of
decrease in MAP and increase in HR. As shown in Fig. 3A, when blood pressure was decreased by about 20% and heart rate was increased by 20–26% (at 30 min after the i.v. administration of 30 mg/kg of benidipine and at 20 min after the i.v. administration of 600 mg/kg of nifedipine), renal resistance was significantly more decreased with benidipine (241.0 6 9.33%) than with nifedipine (220.8 6 13.6%). In contrast, the decrease in HQ vascular resistance was not significantly different between benidipine (241.0 6 17.1%) and nifedipine (236.2 6 19.9%). Both high-dose nifedipine and highdose benidipine showed no significant difference between decrease in renal vascular resistance and that in HQ vascular resistance. From these results, it can be concluded that the vasodilating effect of benidipine is more potent than that of nifedipine in the renal vascular region, and almost equal to that of benidipine in the HQ vascular region when blood pressure is markedly decreased. In contrast, when each drug produced almost the same changes in MAP (about 27%) and HR (about 111%) as shown in Fig. 3B (at 30 min after the i.v. administration of 3 mg/kg of benidipine and at 10 min after the i.v. administration of 100 mg/kg of nifedipine), the decrease in renal vascular resistance was not significantly different between benidipine (217.8 6 2.05%) and nifedipine (210.3 6 11.3%), but HQ vascular resistance was significantly more decreased with benidipine (224.3 6 9.22%) than with nifedipine (25.18 6 17.7%). Benidipine caused no significant difference between the decrease in renal vascular resistance and that in HQ vascular resistance. HQ vascular resistance was almost unchanged with nifedipine. Based on these results, it can be concluded that the vasodilating effect of nifedipine is almost equal to that of benidipine in the renal vascular region, but weaker than that of benidipine in the HQ vascular region when blood pressure is slightly decreased.
Fig. 1. Time courses of mean arterial pressure (top) and heart rate (bottom) after the injection of benidipine (left) or nifedipine (right) in spontaneously hypertensive rats. The doses were 3, 10, and 30 mg/ kg of benidipine and 30, 100, 300, and 600 mg/kg of nifedipine. Each value is the mean 6 SEM of the number of rats shown in parentheses. ***Significant difference between before and after the administration of each calcium antagonist by one-way analysis of variance (ANOVA) at p , 0.001, **p , 0.01, and *p , 0.05.
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Fig. 2. Time courses of renal resistance (top) and hindquarter resistance (bottom) after the injection of benidipine (left) or nifedipine (right) in spontaneously hypertensive rats. The doses were 3, 10, and 30 mg/kg of benidipine and 30, 100, 300, and 600 mg/kg of nifedipine. Each value is the mean 6 SEM of the number of rats shown in parentheses. ***Significant difference between before and after the administration of each calcium antagonist by one-way ANOVA at p , 0.001, **p , 0.01, and *p , 0.05.
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Fig. 3. Comparison of the percent changes in MAP, HR, RF, HQF, RR, and HQR in spontaneously hypertensive rats between (A) 30 min after the administration of benidipine (30 mg/kg) and 20 min after the administration of nifedipine (600 mg/kg), and (B) 30 min after the administration of benidipine (3 mg/kg) and 10 min after the administration of nifedipine (100 mg/kg). Each value is mean 6 SEM. The statistical analysis was performed with the unpaired t test to determine the significance of the differences in benidipine and nifedipine effects in the same artery group. The significance level was set at p , 0.05.
2.4. Effects of benidipine and nifedipine on the renal and HQ vascular regions of the NCRs As shown in Fig. 4, after the administration to NCRs of benidipine at 10 mg/kg, MAP was significantly decreased only at 10 min and then returned to the predose level. Renal resistance was decreased at and after 10 min, but HQ resistance underwent no significant change. After the administration of nifedipine (100 mg/ kg) to NCRs, MAP was significantly decreased at 10 min, returned to the pre-dose level at 20 min, and significantly increased in excess of the pre-dose level at 30 min. Renal resistance was significantly decreased at and after 10 min, but the level was reduced at and after 20 min. HQ resistance underwent no significant change. When 30 mg/kg of benidipine was administered to
NCRs, MAP was significantly decreased at 10 min, and the decrease persisted to 30 min. Not only renal vascular resistance but also HQ vascular resistance was decreased at 10 min, and the decrease persisted for 30 min. When 600 mg/kg of nifedipine was administered, MAP was significantly decreased at 10 min, but tended to increase slightly up to 30 min. HQ vascular resistance showed almost the same time course as MAP, but renal resistance was significantly decreased at 10 min, and the decrease continued to 30 min. A characteristic of both Ca antagonists is that blood pressure and HQ vascular resistance were significantly decreased with a high dose but not with a low dose. As in the SHRs, a local vasodilating effect was compared in NCRs using the dose and time at which the MAP and heart rate were changed to the same extent with benidipine and nifedipine (benidipine: 30 min after the administration of 30 mg/kg, nifedipine: 10 min after the administration of 600 mg/kg). When the MAP and heart rate were changed almost to the same extent by benidipine and nifedipine (blood pressure: decrease by 14–17%, heart rate: increase by 23–28%), the decrease in renal vascular resistance was not significantly different between the benidipine (210.6 6 19.1%) and nifedipine (26.38 6 25.5%) groups. The decrease in HQ vascular resistance was also not significantly different between the benidipine (230.76 11.5%) and nifedipine (239.6 6 7.71%) groups. However, both Ca antagonists showed a vasodilating effect significantly more marked in the HQ vascular region than in the renal vascular region.
3. Discussion 3.1. Vasodilating effects of benidipine and nifedipine on the renal and HQ vascular regions of the SHRs In this study, the antihypertensive effects of benidipine lasted for at least 30 min in a dose-dependent manner in the SHRs, which is in agreement with previously reported findings (Karasawa et al., 1988a, 1988b, 1988c, 1988d, 1988e). After the administration of the highdose benidipine (30 mg/kg), local vascular resistance was decreased not only in the renal region but also in the HQ covering the blood vessels of the lower-extremity muscles, and the effect lasted for 30 min. This is the first demonstration that benidipine has a vasodilating effect on the HQ region. Harashima et al. (1994) previously reported that in conscious SHRs, benidipine at 3 mg/kg showed a vasodilating effect in most of the local vascular regions (the kidneys, lungs, heart, liver, brain, small intestine, pancreas, etc.) except for the muscle. Their finding does not contradict our data because in our study, benidipine (3 mg/kg) did not change the vascular resistance of the HQ region. In SHRs, cardiac output is within the normal range,
Fig. 4. Time courses of MAP, HR, RR, and HQR after the injection of benidipine (10 and 30 mg/kg) or nifedipine (100 and 600 mg/kg) in normotensive control Wistar rats. Each value is the mean 6 SEM of the number of rats shown in parentheses. ***Significant difference between before and after the administration of each calcium antagonist by one-way ANOVA at p , 0.001, **p , 0.01, and *p , 0.05.
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and total peripheral resistance is increased (Ferario and Page, 1978; Smith and Hutchins, 1979; Iriuchijima and Teranishi, 1982); compared with NCRs, SHRs have higher vascular resistance in all of the common carotid, superior mesenteric, renal, and HQ arteries (Iriuchijima, 1983). The region contributing most to the maintenance of hypertension is the HQ region (Iriuchijima, 1985, 1986, 1988). The present results also showed that the HQ blood flow was significantly decreased, but the renal flow was not changed significantly in the SHRs at the resting stage before the drug administration. Both HQ resistance and renal resistance were significantly higher in the SHRs than in the NCRs. However, the difference between SHRs and NCRs was much more pronounced in HQ resistance (Table 1). These findings support the hypothesis that the most important local vascular region in the maintenance of hypertension is the HQ. Therefore, an antihypertensive drug exerting a vasodilating effect in the HQ region is desirable for the treatment of hypertension. In this study, high-dose benidipine (30 mg/kg) showed a long-acting vasodilating effect not only in the renal region but also in the HQ, but with nifedipine in a dose range of 30–300 mg/kg, a vasodilating effect was not observed in the HQ vascular region, though a mild antihypertensive effect was induced. To induce a vasodilating effect in the HQ vascular region, 600 mg/kg of nifedipine (20 times the dose of benidipine) was required. Hence, the vasodilating effect in the HQ region that is characteristic of benidipine is expected to be beneficial in the treatment of neural and hormonal errors complicating hypertension. After the administration of a calcium antagonist, the changes in blood pressure and local hemodynamics are thought to be determined by the sum of the drug’s direct vasodilating effect and compensatory vasoconstriction, including sympathicotonia. In the present study, the change in heart rate was examined as an indicator of reflex sympathicotonia. In agreement with previous findings in conscious dogs (Karasawa et al., 1988b) and rats (Kubo et al., 1985; Karasawa et al., 1988d), benidipine caused a reflex increase in heart rate associated with blood pressure decrease, and both benidipine and nifedipine increased the heart rate of the SHRs in the present study. This implies that both benidipine and nifedipine elevate sympathicotonia. When blood pressure is decreased by the treatment with a nitrous acid agent (Teranishi and Iriuchijima, 1994) or nembutal anesthetic agent (Teranishi and Iriuchijima, 1992) or by minor bleeding (Teranishi and Iriuchijima, 1997) in rats, compensatory vasoconstriction first occurs reflexly in the HQ region, but does not occur reflexly in the renal vascular region. This HQ compensatory action disappears after the administration of a sympathetic ganglionic blocking agent, hexamethonium (C6) (Teranishi and Iriuchijima, 1992, 1994, 1997), after buffer nerve severance (Teranishi and Iriuchijima, 1992) or after
lumbar sympathectomy (unpublished data). These observations suggest that the HQ region has a central role in the compensatory vasopressor mechanism. This mechanism appears to explain the lack of effect of nifedipine at doses of 30–300 mg/kg and benidipine at the lowest dose (3 mg/kg) on the HQ region. In contrast, benidipine at 10–30 mg/kg was characterized by a marked vasodilating effect on the HQ region. This difference is due to the difference in the time course of action between the two drugs. It seems that the renal region was not included in this compensatory vasopressor mechanism because the renal vascular resistance gradually decreased from 10 to 30 min after the administration of low-dose nifedipine or benidipine. In the case of high-dose benidipine (whose vasodilating effect is long-acting), it appears that the compensatory vasopressor mechanism of the sympathetic nerve could not exceed the vasodilating effect in either the renal or HQ regions. 3.2. Comparison of local vasodilating effects of benidipine and nifedipine Since the antihypertensive effects of benidipine and nifedipine differ in extent and time course, the local vasodilating effect of benidipine was compared with that of nifedipine, and the effects were found to be almost the same in decreasing arterial pressure (Fig. 3). When the antihypertensive effect was as large as about 20%, renal vascular resistance was decreased significantly more by benidipine than by nifedipine (Fig. 3A). However, there was no significant difference in HQ vascular resistance between nifedipine and benidipine. These results indicate that at high doses at which the antihypertensive effect is marked, benidipine, which has a longacting vasodilating effect, is more effective specifically against the renal vascular region compared to nifedipine. (The specific vasodilating effect of benidipine on the renal vascular region does not clearly occur at low doses and was thereby not significantly different from the vasodilating effect of nifedipine.) The detailed mechanism of the specific vasodilating effect of benidipine is unknown at present. It was recently reported that benidipine dilates not only the afferent arterioles but also the efferent arterioles. This may contribute to the difference in vasodilating effects on the renal vascular region between benidipine and nifedipine (Kenjirou, 1994). When the antihypertensive effect was about 7%, the decrease in renal resistance was not significantly different between benidipine and nifedipine, but HQ resistance was significantly more decreased with benidipine than with nifedipine (Fig. 3B). These results show that the vasodilating effect of benidipine is similar to that of nifedipine in the renal region but higher in the HQ, indicating that benidipine is characterized by a vasodilating effect in this HQ region. These results suggest that
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the compensatory vasoconstriction reflexly occurring in the HQ vascular region through the sympathetic nervous system can exceed the vasodilating effect of lowdose nifedipine but cannot counteract the potent vasodilating effects of benidipine (which has a long-acting effect) and high-dose nifedipine. In any event, benidipine induces a superior vasodilating effect compared to nifedipine, not only on the HQ vascular region but also on the renal vascular region. In the present study, when blood pressure and heart rate were changed to the almost same extent, the vasodilating effect of benidipine was superior to that of nifedipine in the HQ vascular region at low doses and in the renal vascular region at high doses (Fig. 3), suggesting that cardiac output (mainly stroke volume) or another aspect of local vascular resistance must be at least decreased more with nifedipine than with benidipine (to decrease blood pressure to the same extent as benidipine). This topic remains to be investigated in future studies.
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(3) After the administration of benidipine (10 mg/kg) and nifedipine (100 mg/kg) to NCRs, a vasodilating effect was found in the renal region but not in the HQ, but after the administration of benidipine (100 mg/kg) and nifedipine (600 mg/kg) to NCRs, a vasodilating effect was found not only in the renal region but also in the HQ region.
5. Summary
After the administration of benidipine (30 mg/kg) and nifedipine (100 mg/kg) to NCRs, MAP was decreased only at 10 min and returned to the pre-dose level at 30 min, renal vascular resistance was continuously decreased up to 30 min, and HQ resistance was not changed significantly. At the high dose of both Ca antagonists (benidipine, 100 mg/kg; nifedipine, 600 mg/kg), a vasodilating effect was observed not only in the renal vascular region but also in the HQ vascular region, suggesting that a compensatory constricting effect of the sympathetic nervous system which occurs reflexly as blood pressure decreases exceeds the local vasodilating effects of both Ca antagonists only at low doses, and that the local vasodilating effect is more potent than the compensatory constricting effect at high doses of Ca antagonists, in NCRs as in SHRs. These findings show that in normotensive rats, the pharmacological properties of these two drugs are not significantly different.
We investigated the effects of benidipine and nifedipine on visceral and skeletal muscle blood flow in conscious spontaneously hypertensive rats (SHRs) and normotensive control rats (NCRs). Benidipine (3–30 mg/kg) or nifedipine (30–600 g/kg) was administered in a bolus injection through the jugular vein, and the changes in mean arterial pressure (MAP), renal flow (RF), and hindquarter flow (HQF) covering the blood vessels of the lower extremity muscles were simultaneously monitored for a 30-min period with an indwelling catheter and electromagnetic flowmeter. Renal vascular resistance (RR) and hindquarter resistance (HQR) were calculated as MAP divided by RF and HQF, respectively. When the local vasodilating effects of these two Ca antagonists were compared in SHRs at a high dose administered to reduce the MAP by about 20%, the RR was significantly more decreased by benidipine than nifedipine. The decrease in HQR was not significantly different between benidipine and nifedipine. When a low dose was administered to decrease the blood pressure by about 7%, the decrease in RR was not significantly different between benidipine and nifedipine, but the HQR was significantly more decreased with benidipine than with nifedipine. In the NCRs, no pharmacological properties were significantly different between these two Ca antagonists. These results suggest that benidipine, but not nifedipine, exerts a vasodilating effect not only in the renal region but also in the HQ region of SHRs and could be beneficial in the treatment of neural and hormonal errors complicating hypertension.
4. Conclusion
References
(1) In the SHRs, benidipine showed a higher and longer-acting antihypertensive effect compared to nifedipine. The vasodilating effect of benidipine at 30 mg/ kg was almost equal in the renal and HQ regions, lasting for at least 30 min. In contrast, after the administration of nifedipine at 30–300 mg/kg, a vasodilating effect was found in the renal region, but not in the HQ. (2) At a high dose (600 mg/kg), nifedipine showed a vasodilating effect equal to that of benidipine, also in the HQ region, but its vasodilating effect in the renal vascular region was significantly weaker than that of benidipine.
Clozel, J., 1988. Effects of nitrendipine and cilazapril alone or in combination on hemodynamics and regional blood flows in conscious spontaneously hypertensive rats. J Cardiovasc Pharmacol 12, 600– 607. Ferario, C.M., Page, I.H., 1978. Current views concerning cardiac output in the genesis of experimental hypertension. Circ Res 43, 821– 831. Harashima, H., Kiwada, H., Kajita, J., Kobayashi, S., 1994. Effects of benidipine hydrochloride (Coniel), a new calcium antagonist, on the cardiac output, regional blood flow and vascular resistance in conscious spontaneously hypertensive rats. Biopharmaceutics Drug Disposition 15, 431–438. Iriuchijima, J., 1985. Mechanism of elevation of hindquarter vascular
3.3. Effects of benidipine and nifedipine on the renal and HQ vascular regions of the NCRs
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resistance in spontaneously hypertensive rats. Jpn J Physiol 35, 45–56. Iriuchijima, J., 1986. Regional distribution of sympathetic vasoconstrictor tone in conscious spontaneously hypertensive rats. Jpn J Physiol 36, 1101–1111. Iriuchijima, J., 1988. Abnormal hindquarter vasoconstrictor tone, a feature common to various kinds of hypertensive rats. Jpn J Physiol 38, 545–548. Iriuchijima, J., Teranishi, Y., 1982. Cardiac output in conscious and almost unrestrained spontaneously hypertensive rats. Hiroshima J Med Sci 31, 259–265. Iriuchijima, J., 1983. Regional blood flow in conscious spontaneously hypertensive rats. Jpn J Physiol 33, 41–50. Karasawa, A., Kubo, K., Oka, T., Nakamizo, N., 1988a. Effects of the new calcium antagonist benidipine hydrochloride on cardiohemodynamics in anesthetized dogs. Arzneim-Forsch/Drug Res 38, 1713–1716. Karasawa, A., Ikeda, J., Yamada, K., Kubo, K., Oka, T., Nakamizo, N., 1988b. Anti-hypertensive effects of the new calcium antagonist benidipine hydrochloride in conscious, renal hypertensive dogs. Arzneim-Forsch/Drug Res 38, 1695–1701. Karasawa, A., Kubo, K., Shuto, K., Nakamizo, N., 1988c. Vasodilating effects of the new calcium antagonist benidipine hydrochloride in anesthetized dogs and cats. Arzneim-Forsch/Drug Res 38, 1707–1712. Karasawa, A., Kubo, K., Shuto, K., Oka, T., Nakamizo, N., 1988d. Antihypertensive effects of the new calcium antagonist benidipine hydrochloride in rats. Arzneim-Forsch/Drug Res 38, 1684–1690.
Karasawa, A., Kubo, K., Oka, T., Nakamizo, N., 1988e. Antihypertensive effects of intravenous administration of benidipine hydrochloride and some other calcium antagonist in conscious, spontaneously hypertensive rats. Arzneim-Forsch/Drug Res 38, 1691– 1694. Kenjirou, K., 1994. Effects of benidipine hydrochloride on renal arterioles. Ther Res 15, 2337–2340. Kubo, K., Karasawa, A., Shuto, K., Nakamizo, N., 1985. Antihypertensive effects of a novel dihydropyridine-type Ca antagonist, KW-3049. Jpn J Pharmacol 39 (Suppl.), 217P. Shimamoto, H., Shimamoto, Y., 1997. Benidipine counteracts sodium-induced alterations in systemic and regional hemodynamics. Blood Press 6, 18–23. Smith, T.L., Hutchins, P.M., 1979. Central hemodynamics in the developmental stage of spontaneous hypertension in the unanesthetized rats. Hypertension 1, 508–511. Terada, K., Nakao, K., Okabe, K., Okabe, K., Kitamura, K., Kuriyama, H., 1987. Action of the 1,4-dihydropyridine derivative, KW3049, on the smooth muscle membrane of the rabbit mesenteric artery. Br J Pharmacol 92, 615–625. Teranishi, Y., Iriuchijima, J., 1992. Sympathetic vasoconstrictor tone induced by pentobarbital anesthesia in hindquarters of rats. Jpn J Physiol 42, 171–178. Teranishi, Y., Iriuchijima, J., 1994. Hindquarter vascular resistance as compensator for hypotension in conscious rats. Tohoku J Exp Med 173, 283–289. Teranishi, Y., Iriuchijima, J., 1997. Hindquarter sympathetic tone induced by small blood loss in conscious rats. Tohoku J Exp Med 182, 69–73.
Vasodilating effect of benidipine hydrochloride in the renal and hindquarter vascular regions (supplied by terminal aorta) of spontaneously hypertensive rats Yasuhiro Teranishia,*, Ryoji Ozonob, Atsunori Yoshimizuc, Atsushi Uedac, Satoshi Kurisuc, Hiromichi Tsurud a Department of Physiology, Hiroshima University, School of Medicine, Minami-ku, Hiroshima 734-8551, Japan Department of Clinical Laboratory Medicine, Hiroshima University, School of Medicine, Minami-ku, Hiroshima 734-8551, Japan c First Department of Internal Medicine, Hiroshima University, School of Medicine, Minami-ku, Hiroshima 734-8551, Japan d Department of Pharmacology, Toho University School of Medicine, Ohta-ku, Tokyo 143-8540, Japan Received 12 August 1998; accepted 21 December 1998
b
Abstract One of two Ca antagonists, benidipine (3–30 mg/kg) or nifedipine (30–600 g/kg), was administered in a bolus injection through the jugular vein, and the changes in mean arterial pressure (MAP), renal flow (RF), and hindquarter flow (HQF) in conscious spontaneously hypertensive rats (SHRs) and normotensive control rats (NCRs). Renal vascular resistance (RR) and hindquarter resistance (HQR) were calculated as MAP divided by RF and HQF, respectively. When a high dose was administered to decrease the blood pressure by about 20%, the RR was significantly lower with benidipine than with nifedipine. The decrease in HQR was not significantly different between benidipine and nifedipine. When a low dose was administered to decrease the blood pressure by about 7%, the decrease in RR was not significantly different between benidipine and nifedipine, but the HQR was significantly lower with benidipine than with nifedipine. In the NCRs, no pharmacological properties were significantly different between these two Ca antagonists. 1999 Elsevier Science Inc. All rights reserved. Keywords: Benidipine; Calcium antagonist; Renal resistance; Hindquarter resistance; Skeletal muscle vascular resistance; SHR
In patients with essential hypertension as well as animals with experimental hypertension, regional vascular flow and vascular resistance are not homogenous. In addition, the effects of antihypertensive drugs, including calcium antagonists, are not the same in the treatment of essential hypertension. Among these drugs, benidipine hydrochloride is a dihydropyridine (DHP) calcium antagonist that is thought to exert its effect by inhibiting the slow inward calcium ion current in smooth muscle cells (Terada et al., 1987). The antihypertensive effects of benidipine in dogs (Karasawa et al., 1988a, 1988b), cats (Karasawa et al., 1988c), rats (Karasawa et al., 1988d, 1988e), and humans (Shimamoto and Shimamoto, 1997) are long-acting and have a slow onset compared with other calcium antagonists. In conscious spontaneously hypertensive rats (SHRs), benidipine has been observed to have long-acting antihypertensive * Corresponding author. Tel.: 181-82-257-5126; fax: 181-82-2575187. E-mail address: [email protected] (Y. Teranishi)
effects of increasing cardiac output and decreasing total peripheral vascular resistance (TPR). In particular, benidipine vasodilating effect in the cardiac (coronary artery) and renal regions has been reported to be remarkable (Harashima et al., 1994), and it also showed a vasodilating effect in most regional vascular regions but had no effect on skeletal muscle (Harashima et al., 1994). Similar peripheral vasodilation was produced by another calcium antagonist, nitrendipine (Clozel, 1988). However, in our early studies, we observed that the vasodilating effect of benidipine was more marked than that of nifedipine in the hindquarter (HQ) vascular region (most of it is thought to cover vessels of the lower extremity muscle) of unanesthetized and unrestrained SHRs, while in the renal vascular region, there was no significant difference between the two Ca antagonists in vasodilating effects. However, it has recently been reported that benidipine has a specific vasodilating effect on the renal vascular region, which other Ca antagonists do not have (Kenjirou, 1994). To explore these contradictions, we observed the an-
0306-3623/99/$ – see front matter 1999 Elsevier Science Inc. All rights reserved. PII: S0306-3623(99)00003-8
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tihypertensive effects of benidipine and nifedipine at wide-ranging doses and chose the doses and times at which the antihypertensive effect and heart rate were changed to the same extent. We then compared the renal vasodilating effect and the HQ vascular vasodilating effect of benidipine with those of nifedipine measured simultaneously. Among the many Ca antagonists, Ca antagonists that improve renal blood flow and prevent the induction of renal failure are generally believed to be the best, while it is the skeletal muscles that are a key vascular region contributing to the maintenance of hypertension in SHRs because a marked elevation of skeletal muscle vascular resistance contributes to the increase in the TPR of SHRs (Iriuchijima, 1985, 1986, 1988), and because hypertension of SHRs is maintained by an increase in the TPR (Ferario and Page, 1978; Iriuchijima and Teranishi, 1982; Smith and Hutchins, 1979). Hence, the skeletal muscle is also an important vascular region that should be improved.
was observed for 20 to 30 min in its home cage. Then, the SHRs were treated with benidipine (3–30 mg/kg) or nifedipine (30–600 mg/kg) in a bolus i.v. injection, and arterial pressure, heart rate, and respective local blood flows were measured every 10 min for 30 min. Renal and HQ vascular resistances were calculated by dividing the arterial pressure by the simultaneously measured local blood flow. The NCRs were treated with benidipine (10 or 30 mg/kg) or nifedipine (100 or 600 mg/ kg) by i.v. injection, and similar measurements were performed. The arterial pressure values were smoothed with a resistance and capacitance (RC) filter with a time constant of 1 s and recorded by a pen writer. Each flow probe was calibrated before implantation by passing known amounts of saline through the excised artery. Flow signals were integrated with a time constant of 1 s to obtain the mean flow. The blood flow and local vascular resistance data were normalized to values per 100 g of body weight for comparison. 1.3. Drugs used
1. Materials and methods 1.1. Experimental animals and operation Male SHRs and normotensive control Wistar rats (NCRs) at 14–16 weeks of age were anesthetized with 50 mg/kg of thiamylal sodium by intraperitoneal injection, and either the right renal artery or the terminal abdominal aorta (most of the blood flow measured there is considered to be that of the lower-extremity muscles) was equipped with the probe (1.0- and 2.0-mm inside diameters, respectively) of an electromagnetic flowmeter (Nihon Kohden Co., Tokyo). At the same time, a cannula (PE-50) for arterial pressure measurement was inserted from the right common carotid artery to near the aortic arch. Another cannula (PE-10 fused to PE-20) for the i.v. injection of the calcium antagonist was inserted into the right jugular vein. The opposite end of each tube was exteriorized at the neck. The SHRs and Wistar rats were purchased from Charles River Japan Inc. (Yokohama, Japan). 1.2. Measurements of arterial pressure, heart rate, and local blood flow After the instrumentation operation described above, the rats were housed separately in plastic cages that measured 35 3 30 3 17 (depth) cm and were lined with wood chips. The rats were allowed ad libitum food pellets and drinking water. Three days after fixation of the electromagnetic flowmeter probe and cannulation, the rats’ arterial pressure, heart rate, and blood flow of the renal artery or terminal abdominal aorta (hereafter referred to as the hindquarter [HQ]) were measured simultaneously. First, to examine hemodynamics at the resting stage, each rat was allowed to freely behave and
Thiamylal sodium (Isozol, Yoshitomi Pharmaceuticals, Osaka, Japan) was used in the present study. Benidipine and nifedipine were gifts from Kyowa Hakko Kogyo Co. (Tokyo, Japan). Each Ca antagonist was kneaded well with a drop of polyoxyethylene (20) sorbitan monooleate in a mortar and then diluted with isotonic sodium chloride solution to adjust the concentration to 1000 mg/ml. 1.4. Statistical analysis All values are expressed as mean 6 SD. One-way analysis of variance (ANOVA) followed by Dunnett’s test was used to examine the changes after the administration of the two calcium antagonists (differences from pre-dose data). The statistical analysis was performed with the unpaired t test to determine the significance of the differences between the renal group and the HQ group treated with the same drug, at the same dose, and at the same time point, and also the differences between benidipine and nifedipine effects in the same artery group. The significance level was set at p , 0.05.
2. Results 2.1. Comparison of each parameter at the resting stage (before the administration of a calcium antagonist) between SHRs and NCRs Mean arterial pressure (MAP), renal and HQ blood flows, and renal and HQ vascular resistances at the resting stage were compared between SHRs and NCRs (Table 1). In the SHRs, MAP was significantly higher (p , 0.001), the renal flow was not changed, the HQ flow was significantly decreased (p , 0.001), and the re-
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Table 1 Mean arterial pressure (MAP), renal flow (RF), hindquarter flow (HQF), renal resistance (RR), and hindquarter resistance (HQR) at the resting stage before drug administration in spontaneously hypertensive rats (SHR) and normotensive control rats (NCR) Group
n
MAP
RF
HQF
RR
HQR
SHR Renal SHR Hindq Total
49
157 6 144
1.97 6 0.47
—
84.4 6 22.7*
—
44
156 6 14.7
—
3.42 6 0.84*
—
48.2 6 12.2*
93
157 6 14.5*
23
116 6 8.38
2.07 6 0.50
—
59.9 6 16.9
—
29
113 6 10.5
—
4.46 6 1.02
—
26.3 6 5.23
52
114 6 9.68
NCR Renal NCR Hindq Total
Each value is the mean 6 SD of n rats. * Each difference between SHR and NCR was significant at p , 0.001.
nal and HQ vascular resistances were significantly increased (p , 0.001). 2.2. Effects of benidipine and nifedipine on the renal and HQ vascular regions of the SHRs After the administration of benidipine, MAP was significantly decreased in a dose-dependent manner, and this antihypertensive effect lasted for at least 30 min (Fig. 1, top left). Renal vascular resistance (RR), calculated by MAP/renal blood flow (RF), also showed a similar dose-dependent decrease, which lasted up to 30 min (Fig. 2, top left). The HQ resistance was significantly decreased up to 30 min after the administration of high-dose benidipine (30 mg/kg) (Fig. 2, bottom left). In contrast, after the administration of nifedipine, MAP was transiently decreased at 10 min, but increased thereafter and returned to the pre-dose level at 30 min (Fig. 1, top right). Renal resistance was significantly decreased at and after 10 min, at only two doses (30 mg/ kg and 600 mg/kg), and it was significantly decreased up to 30 min after the administration of nifedipine at doses of 30, 100, and 600 mg/kg; however, at the dose of 300 mg/kg, it was transiently decreased at 10 min but increased thereafter to the pre-dose level (Fig. 2, top right). HQ resistance underwent no significant change after the administration of nifedipine at doses of 30, 100, and 300 mg/kg, but it was significantly decreased up to 30 min after the administration of the highest dose (600 mg/kg) (Fig. 2, bottom right). Both benidipine and nifedipine significantly increased heart rate at and after 20 min (Fig. 1, bottom). 2.3. Comparison of local vasodilating effects between benidipine and nifedipine Since the antihypertensive effects of benidipine and nifedipine differed in extent and time course, a local vasodilating effect was compared at the dose and time at which each drug produced almost the same extent of
decrease in MAP and increase in HR. As shown in Fig. 3A, when blood pressure was decreased by about 20% and heart rate was increased by 20–26% (at 30 min after the i.v. administration of 30 mg/kg of benidipine and at 20 min after the i.v. administration of 600 mg/kg of nifedipine), renal resistance was significantly more decreased with benidipine (241.0 6 9.33%) than with nifedipine (220.8 6 13.6%). In contrast, the decrease in HQ vascular resistance was not significantly different between benidipine (241.0 6 17.1%) and nifedipine (236.2 6 19.9%). Both high-dose nifedipine and highdose benidipine showed no significant difference between decrease in renal vascular resistance and that in HQ vascular resistance. From these results, it can be concluded that the vasodilating effect of benidipine is more potent than that of nifedipine in the renal vascular region, and almost equal to that of benidipine in the HQ vascular region when blood pressure is markedly decreased. In contrast, when each drug produced almost the same changes in MAP (about 27%) and HR (about 111%) as shown in Fig. 3B (at 30 min after the i.v. administration of 3 mg/kg of benidipine and at 10 min after the i.v. administration of 100 mg/kg of nifedipine), the decrease in renal vascular resistance was not significantly different between benidipine (217.8 6 2.05%) and nifedipine (210.3 6 11.3%), but HQ vascular resistance was significantly more decreased with benidipine (224.3 6 9.22%) than with nifedipine (25.18 6 17.7%). Benidipine caused no significant difference between the decrease in renal vascular resistance and that in HQ vascular resistance. HQ vascular resistance was almost unchanged with nifedipine. Based on these results, it can be concluded that the vasodilating effect of nifedipine is almost equal to that of benidipine in the renal vascular region, but weaker than that of benidipine in the HQ vascular region when blood pressure is slightly decreased.
Fig. 1. Time courses of mean arterial pressure (top) and heart rate (bottom) after the injection of benidipine (left) or nifedipine (right) in spontaneously hypertensive rats. The doses were 3, 10, and 30 mg/ kg of benidipine and 30, 100, 300, and 600 mg/kg of nifedipine. Each value is the mean 6 SEM of the number of rats shown in parentheses. ***Significant difference between before and after the administration of each calcium antagonist by one-way analysis of variance (ANOVA) at p , 0.001, **p , 0.01, and *p , 0.05.
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Fig. 2. Time courses of renal resistance (top) and hindquarter resistance (bottom) after the injection of benidipine (left) or nifedipine (right) in spontaneously hypertensive rats. The doses were 3, 10, and 30 mg/kg of benidipine and 30, 100, 300, and 600 mg/kg of nifedipine. Each value is the mean 6 SEM of the number of rats shown in parentheses. ***Significant difference between before and after the administration of each calcium antagonist by one-way ANOVA at p , 0.001, **p , 0.01, and *p , 0.05.
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Fig. 3. Comparison of the percent changes in MAP, HR, RF, HQF, RR, and HQR in spontaneously hypertensive rats between (A) 30 min after the administration of benidipine (30 mg/kg) and 20 min after the administration of nifedipine (600 mg/kg), and (B) 30 min after the administration of benidipine (3 mg/kg) and 10 min after the administration of nifedipine (100 mg/kg). Each value is mean 6 SEM. The statistical analysis was performed with the unpaired t test to determine the significance of the differences in benidipine and nifedipine effects in the same artery group. The significance level was set at p , 0.05.
2.4. Effects of benidipine and nifedipine on the renal and HQ vascular regions of the NCRs As shown in Fig. 4, after the administration to NCRs of benidipine at 10 mg/kg, MAP was significantly decreased only at 10 min and then returned to the predose level. Renal resistance was decreased at and after 10 min, but HQ resistance underwent no significant change. After the administration of nifedipine (100 mg/ kg) to NCRs, MAP was significantly decreased at 10 min, returned to the pre-dose level at 20 min, and significantly increased in excess of the pre-dose level at 30 min. Renal resistance was significantly decreased at and after 10 min, but the level was reduced at and after 20 min. HQ resistance underwent no significant change. When 30 mg/kg of benidipine was administered to
NCRs, MAP was significantly decreased at 10 min, and the decrease persisted to 30 min. Not only renal vascular resistance but also HQ vascular resistance was decreased at 10 min, and the decrease persisted for 30 min. When 600 mg/kg of nifedipine was administered, MAP was significantly decreased at 10 min, but tended to increase slightly up to 30 min. HQ vascular resistance showed almost the same time course as MAP, but renal resistance was significantly decreased at 10 min, and the decrease continued to 30 min. A characteristic of both Ca antagonists is that blood pressure and HQ vascular resistance were significantly decreased with a high dose but not with a low dose. As in the SHRs, a local vasodilating effect was compared in NCRs using the dose and time at which the MAP and heart rate were changed to the same extent with benidipine and nifedipine (benidipine: 30 min after the administration of 30 mg/kg, nifedipine: 10 min after the administration of 600 mg/kg). When the MAP and heart rate were changed almost to the same extent by benidipine and nifedipine (blood pressure: decrease by 14–17%, heart rate: increase by 23–28%), the decrease in renal vascular resistance was not significantly different between the benidipine (210.6 6 19.1%) and nifedipine (26.38 6 25.5%) groups. The decrease in HQ vascular resistance was also not significantly different between the benidipine (230.76 11.5%) and nifedipine (239.6 6 7.71%) groups. However, both Ca antagonists showed a vasodilating effect significantly more marked in the HQ vascular region than in the renal vascular region.
3. Discussion 3.1. Vasodilating effects of benidipine and nifedipine on the renal and HQ vascular regions of the SHRs In this study, the antihypertensive effects of benidipine lasted for at least 30 min in a dose-dependent manner in the SHRs, which is in agreement with previously reported findings (Karasawa et al., 1988a, 1988b, 1988c, 1988d, 1988e). After the administration of the highdose benidipine (30 mg/kg), local vascular resistance was decreased not only in the renal region but also in the HQ covering the blood vessels of the lower-extremity muscles, and the effect lasted for 30 min. This is the first demonstration that benidipine has a vasodilating effect on the HQ region. Harashima et al. (1994) previously reported that in conscious SHRs, benidipine at 3 mg/kg showed a vasodilating effect in most of the local vascular regions (the kidneys, lungs, heart, liver, brain, small intestine, pancreas, etc.) except for the muscle. Their finding does not contradict our data because in our study, benidipine (3 mg/kg) did not change the vascular resistance of the HQ region. In SHRs, cardiac output is within the normal range,
Fig. 4. Time courses of MAP, HR, RR, and HQR after the injection of benidipine (10 and 30 mg/kg) or nifedipine (100 and 600 mg/kg) in normotensive control Wistar rats. Each value is the mean 6 SEM of the number of rats shown in parentheses. ***Significant difference between before and after the administration of each calcium antagonist by one-way ANOVA at p , 0.001, **p , 0.01, and *p , 0.05.
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and total peripheral resistance is increased (Ferario and Page, 1978; Smith and Hutchins, 1979; Iriuchijima and Teranishi, 1982); compared with NCRs, SHRs have higher vascular resistance in all of the common carotid, superior mesenteric, renal, and HQ arteries (Iriuchijima, 1983). The region contributing most to the maintenance of hypertension is the HQ region (Iriuchijima, 1985, 1986, 1988). The present results also showed that the HQ blood flow was significantly decreased, but the renal flow was not changed significantly in the SHRs at the resting stage before the drug administration. Both HQ resistance and renal resistance were significantly higher in the SHRs than in the NCRs. However, the difference between SHRs and NCRs was much more pronounced in HQ resistance (Table 1). These findings support the hypothesis that the most important local vascular region in the maintenance of hypertension is the HQ. Therefore, an antihypertensive drug exerting a vasodilating effect in the HQ region is desirable for the treatment of hypertension. In this study, high-dose benidipine (30 mg/kg) showed a long-acting vasodilating effect not only in the renal region but also in the HQ, but with nifedipine in a dose range of 30–300 mg/kg, a vasodilating effect was not observed in the HQ vascular region, though a mild antihypertensive effect was induced. To induce a vasodilating effect in the HQ vascular region, 600 mg/kg of nifedipine (20 times the dose of benidipine) was required. Hence, the vasodilating effect in the HQ region that is characteristic of benidipine is expected to be beneficial in the treatment of neural and hormonal errors complicating hypertension. After the administration of a calcium antagonist, the changes in blood pressure and local hemodynamics are thought to be determined by the sum of the drug’s direct vasodilating effect and compensatory vasoconstriction, including sympathicotonia. In the present study, the change in heart rate was examined as an indicator of reflex sympathicotonia. In agreement with previous findings in conscious dogs (Karasawa et al., 1988b) and rats (Kubo et al., 1985; Karasawa et al., 1988d), benidipine caused a reflex increase in heart rate associated with blood pressure decrease, and both benidipine and nifedipine increased the heart rate of the SHRs in the present study. This implies that both benidipine and nifedipine elevate sympathicotonia. When blood pressure is decreased by the treatment with a nitrous acid agent (Teranishi and Iriuchijima, 1994) or nembutal anesthetic agent (Teranishi and Iriuchijima, 1992) or by minor bleeding (Teranishi and Iriuchijima, 1997) in rats, compensatory vasoconstriction first occurs reflexly in the HQ region, but does not occur reflexly in the renal vascular region. This HQ compensatory action disappears after the administration of a sympathetic ganglionic blocking agent, hexamethonium (C6) (Teranishi and Iriuchijima, 1992, 1994, 1997), after buffer nerve severance (Teranishi and Iriuchijima, 1992) or after
lumbar sympathectomy (unpublished data). These observations suggest that the HQ region has a central role in the compensatory vasopressor mechanism. This mechanism appears to explain the lack of effect of nifedipine at doses of 30–300 mg/kg and benidipine at the lowest dose (3 mg/kg) on the HQ region. In contrast, benidipine at 10–30 mg/kg was characterized by a marked vasodilating effect on the HQ region. This difference is due to the difference in the time course of action between the two drugs. It seems that the renal region was not included in this compensatory vasopressor mechanism because the renal vascular resistance gradually decreased from 10 to 30 min after the administration of low-dose nifedipine or benidipine. In the case of high-dose benidipine (whose vasodilating effect is long-acting), it appears that the compensatory vasopressor mechanism of the sympathetic nerve could not exceed the vasodilating effect in either the renal or HQ regions. 3.2. Comparison of local vasodilating effects of benidipine and nifedipine Since the antihypertensive effects of benidipine and nifedipine differ in extent and time course, the local vasodilating effect of benidipine was compared with that of nifedipine, and the effects were found to be almost the same in decreasing arterial pressure (Fig. 3). When the antihypertensive effect was as large as about 20%, renal vascular resistance was decreased significantly more by benidipine than by nifedipine (Fig. 3A). However, there was no significant difference in HQ vascular resistance between nifedipine and benidipine. These results indicate that at high doses at which the antihypertensive effect is marked, benidipine, which has a longacting vasodilating effect, is more effective specifically against the renal vascular region compared to nifedipine. (The specific vasodilating effect of benidipine on the renal vascular region does not clearly occur at low doses and was thereby not significantly different from the vasodilating effect of nifedipine.) The detailed mechanism of the specific vasodilating effect of benidipine is unknown at present. It was recently reported that benidipine dilates not only the afferent arterioles but also the efferent arterioles. This may contribute to the difference in vasodilating effects on the renal vascular region between benidipine and nifedipine (Kenjirou, 1994). When the antihypertensive effect was about 7%, the decrease in renal resistance was not significantly different between benidipine and nifedipine, but HQ resistance was significantly more decreased with benidipine than with nifedipine (Fig. 3B). These results show that the vasodilating effect of benidipine is similar to that of nifedipine in the renal region but higher in the HQ, indicating that benidipine is characterized by a vasodilating effect in this HQ region. These results suggest that
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the compensatory vasoconstriction reflexly occurring in the HQ vascular region through the sympathetic nervous system can exceed the vasodilating effect of lowdose nifedipine but cannot counteract the potent vasodilating effects of benidipine (which has a long-acting effect) and high-dose nifedipine. In any event, benidipine induces a superior vasodilating effect compared to nifedipine, not only on the HQ vascular region but also on the renal vascular region. In the present study, when blood pressure and heart rate were changed to the almost same extent, the vasodilating effect of benidipine was superior to that of nifedipine in the HQ vascular region at low doses and in the renal vascular region at high doses (Fig. 3), suggesting that cardiac output (mainly stroke volume) or another aspect of local vascular resistance must be at least decreased more with nifedipine than with benidipine (to decrease blood pressure to the same extent as benidipine). This topic remains to be investigated in future studies.
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(3) After the administration of benidipine (10 mg/kg) and nifedipine (100 mg/kg) to NCRs, a vasodilating effect was found in the renal region but not in the HQ, but after the administration of benidipine (100 mg/kg) and nifedipine (600 mg/kg) to NCRs, a vasodilating effect was found not only in the renal region but also in the HQ region.
5. Summary
After the administration of benidipine (30 mg/kg) and nifedipine (100 mg/kg) to NCRs, MAP was decreased only at 10 min and returned to the pre-dose level at 30 min, renal vascular resistance was continuously decreased up to 30 min, and HQ resistance was not changed significantly. At the high dose of both Ca antagonists (benidipine, 100 mg/kg; nifedipine, 600 mg/kg), a vasodilating effect was observed not only in the renal vascular region but also in the HQ vascular region, suggesting that a compensatory constricting effect of the sympathetic nervous system which occurs reflexly as blood pressure decreases exceeds the local vasodilating effects of both Ca antagonists only at low doses, and that the local vasodilating effect is more potent than the compensatory constricting effect at high doses of Ca antagonists, in NCRs as in SHRs. These findings show that in normotensive rats, the pharmacological properties of these two drugs are not significantly different.
We investigated the effects of benidipine and nifedipine on visceral and skeletal muscle blood flow in conscious spontaneously hypertensive rats (SHRs) and normotensive control rats (NCRs). Benidipine (3–30 mg/kg) or nifedipine (30–600 g/kg) was administered in a bolus injection through the jugular vein, and the changes in mean arterial pressure (MAP), renal flow (RF), and hindquarter flow (HQF) covering the blood vessels of the lower extremity muscles were simultaneously monitored for a 30-min period with an indwelling catheter and electromagnetic flowmeter. Renal vascular resistance (RR) and hindquarter resistance (HQR) were calculated as MAP divided by RF and HQF, respectively. When the local vasodilating effects of these two Ca antagonists were compared in SHRs at a high dose administered to reduce the MAP by about 20%, the RR was significantly more decreased by benidipine than nifedipine. The decrease in HQR was not significantly different between benidipine and nifedipine. When a low dose was administered to decrease the blood pressure by about 7%, the decrease in RR was not significantly different between benidipine and nifedipine, but the HQR was significantly more decreased with benidipine than with nifedipine. In the NCRs, no pharmacological properties were significantly different between these two Ca antagonists. These results suggest that benidipine, but not nifedipine, exerts a vasodilating effect not only in the renal region but also in the HQ region of SHRs and could be beneficial in the treatment of neural and hormonal errors complicating hypertension.
4. Conclusion
References
(1) In the SHRs, benidipine showed a higher and longer-acting antihypertensive effect compared to nifedipine. The vasodilating effect of benidipine at 30 mg/ kg was almost equal in the renal and HQ regions, lasting for at least 30 min. In contrast, after the administration of nifedipine at 30–300 mg/kg, a vasodilating effect was found in the renal region, but not in the HQ. (2) At a high dose (600 mg/kg), nifedipine showed a vasodilating effect equal to that of benidipine, also in the HQ region, but its vasodilating effect in the renal vascular region was significantly weaker than that of benidipine.
Clozel, J., 1988. Effects of nitrendipine and cilazapril alone or in combination on hemodynamics and regional blood flows in conscious spontaneously hypertensive rats. J Cardiovasc Pharmacol 12, 600– 607. Ferario, C.M., Page, I.H., 1978. Current views concerning cardiac output in the genesis of experimental hypertension. Circ Res 43, 821– 831. Harashima, H., Kiwada, H., Kajita, J., Kobayashi, S., 1994. Effects of benidipine hydrochloride (Coniel), a new calcium antagonist, on the cardiac output, regional blood flow and vascular resistance in conscious spontaneously hypertensive rats. Biopharmaceutics Drug Disposition 15, 431–438. Iriuchijima, J., 1985. Mechanism of elevation of hindquarter vascular
3.3. Effects of benidipine and nifedipine on the renal and HQ vascular regions of the NCRs
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Y. Teranishi et al. / General Pharmacology 33 (1999) 127–136
resistance in spontaneously hypertensive rats. Jpn J Physiol 35, 45–56. Iriuchijima, J., 1986. Regional distribution of sympathetic vasoconstrictor tone in conscious spontaneously hypertensive rats. Jpn J Physiol 36, 1101–1111. Iriuchijima, J., 1988. Abnormal hindquarter vasoconstrictor tone, a feature common to various kinds of hypertensive rats. Jpn J Physiol 38, 545–548. Iriuchijima, J., Teranishi, Y., 1982. Cardiac output in conscious and almost unrestrained spontaneously hypertensive rats. Hiroshima J Med Sci 31, 259–265. Iriuchijima, J., 1983. Regional blood flow in conscious spontaneously hypertensive rats. Jpn J Physiol 33, 41–50. Karasawa, A., Kubo, K., Oka, T., Nakamizo, N., 1988a. Effects of the new calcium antagonist benidipine hydrochloride on cardiohemodynamics in anesthetized dogs. Arzneim-Forsch/Drug Res 38, 1713–1716. Karasawa, A., Ikeda, J., Yamada, K., Kubo, K., Oka, T., Nakamizo, N., 1988b. Anti-hypertensive effects of the new calcium antagonist benidipine hydrochloride in conscious, renal hypertensive dogs. Arzneim-Forsch/Drug Res 38, 1695–1701. Karasawa, A., Kubo, K., Shuto, K., Nakamizo, N., 1988c. Vasodilating effects of the new calcium antagonist benidipine hydrochloride in anesthetized dogs and cats. Arzneim-Forsch/Drug Res 38, 1707–1712. Karasawa, A., Kubo, K., Shuto, K., Oka, T., Nakamizo, N., 1988d. Antihypertensive effects of the new calcium antagonist benidipine hydrochloride in rats. Arzneim-Forsch/Drug Res 38, 1684–1690.
Karasawa, A., Kubo, K., Oka, T., Nakamizo, N., 1988e. Antihypertensive effects of intravenous administration of benidipine hydrochloride and some other calcium antagonist in conscious, spontaneously hypertensive rats. Arzneim-Forsch/Drug Res 38, 1691– 1694. Kenjirou, K., 1994. Effects of benidipine hydrochloride on renal arterioles. Ther Res 15, 2337–2340. Kubo, K., Karasawa, A., Shuto, K., Nakamizo, N., 1985. Antihypertensive effects of a novel dihydropyridine-type Ca antagonist, KW-3049. Jpn J Pharmacol 39 (Suppl.), 217P. Shimamoto, H., Shimamoto, Y., 1997. Benidipine counteracts sodium-induced alterations in systemic and regional hemodynamics. Blood Press 6, 18–23. Smith, T.L., Hutchins, P.M., 1979. Central hemodynamics in the developmental stage of spontaneous hypertension in the unanesthetized rats. Hypertension 1, 508–511. Terada, K., Nakao, K., Okabe, K., Okabe, K., Kitamura, K., Kuriyama, H., 1987. Action of the 1,4-dihydropyridine derivative, KW3049, on the smooth muscle membrane of the rabbit mesenteric artery. Br J Pharmacol 92, 615–625. Teranishi, Y., Iriuchijima, J., 1992. Sympathetic vasoconstrictor tone induced by pentobarbital anesthesia in hindquarters of rats. Jpn J Physiol 42, 171–178. Teranishi, Y., Iriuchijima, J., 1994. Hindquarter vascular resistance as compensator for hypotension in conscious rats. Tohoku J Exp Med 173, 283–289. Teranishi, Y., Iriuchijima, J., 1997. Hindquarter sympathetic tone induced by small blood loss in conscious rats. Tohoku J Exp Med 182, 69–73.