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The effects of calcium channel blockers, verapamil, nifedipine and diltiazem, on metabolic control in diabetic rats
Diabetes Research and Clinical Practice 28 (1995) 201-205
ELSEVIER
The effects of calcium channel blockers, verapamil, nifedipine and diltiazem, on metabolic control in diabetic rats Alev Akdogan
Kaymaz*a, Hiiseyin Tana, Tuncay Altugb, A. Sevim Btiyi.ikdevrimb
“Department of Internal Medicine. Faculty of Veterinary Medicine, isranbul Universi[y, Avcilar 34851, Istanbul, Turkey blnstitute for Experimental Medical Research (DETAM), isranbul University, Istanbul, Turkey
Received 27 April 1993; revision received 2 May 1995;accepted 3 June 1995
Abstract The effects of calcium channel blockers (CCB)-verapamil, nifedipine, diltiazem on metabolic control in streptozotocin-induced long-term diabetes in rats were investigated. Diabetes mellitus was induced by single intravenous injection of streptozotocin (65 mgikg body wt.). The animals were divided into live groups: a healthy control group, a diabetic group and three diabetic groups treated with one of the calcium channel blockers (verapamil, 25 mg/kg/day, nifedipine, 20 mg/kg/day, and diltiazem, 30 mg/kg/day, respectively). Body weight, glycemia, glycated hemoglobin and total serum protein levels of these animals were measured at the beginning and at the end (after 13 weeks) of the experiment. It was observed that diabetic animals who were not treated with CCB had lost weight at the end of the experiment (P < 0.01). The blood glucose and glycated hemoglobin levels were increasedin the diabetic group in comparison to the healthy control group (P < 0.001). However, the calcium channel blockers seem to have beneficial effects on body weight, glycated hemoglobin and blood glucose levels. Keywmk
Calcium channel blockers; Diabetes mellitus; Streptozotocin; Metabolic control
1. Introduction
parallel
to the observation
mentioned
above,
Dunbar et al. [2] have observed that the 0 cell It has been shown that intracellular deposition of calcium increases in diabetic animals induced by streptozotocin [6]. It has also been reported that intracellular calcium levels of platelets [7,8] and erythrocytes [9] increased in streptozotocindiabetic rats. In addition to these findings, hyperglycemia inhibits Ca 2+-ATPase and increases intracellular calcium concentrations [l-5]. In l
Corresponding author.
desensitization to glucose induced by hyperglycemia is augmented by increased calcium levels within the islets. Gronda et al. [4] have reported that D-glucose shows inhibitory action on the Ca2+-ATPase activity of the plasma membranes of the pancreatic 0 cells. An alternative hypothesis is that glycated proteins which increase in diabetes bind higher amounts of calcium [lo- 131. Whether increase in intracellular calcium levels is a primary event
0168-8227/95/%09.500 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0168-8227(95)01090-Z
202
A.A. Kaymaz et al. /Diabetes
Research and Clinical Practice 28 (1995) 2OI-205
leading to complication, or an aftermath of increased non-enzymatic glycation, or both, is not clear yet. From this evidence, it seemsattractive to us to investigate the beneficial effects, if any, of different kinds of calcium channel blockers upon the metabolic control parameters in diabetic rats induced by streptozotocin.
Table 1 Body weights of the animals (mean i S.D.) Groups
n
Before treatmerit (g)
After 13 weeks of treatment (g)
I II
5 9 9 8 9
199 zt 192 f 199 f 191 f 199 f
310 l 15*q 147 l 27**-t,t 165 zt 30****$ 161 A 41$ 182 f 19tv$
III
2. Materials and methods Male Wistar albino rats, weighing approximately 200 g bred at the Institute for Experimental Medical Research (DETAM) of Istanbul University, were used. Diabetes mellitus was induced by a single intraveneous injection of streptozotocin in a dose of 65 mglkg body weight. Streptozotocin was dissolved in a citrate buffer at pH 4.5. The control group received only citrate buffer at the sameamount. The animals whose blood sugar levels were higher than 15 mM at the 48-h postinjection period were included in this study, and five experimental groups were established as follows: (I) healthy control group (n = 5); (II) diabetic group alone (n = 9); (III) diabetic group treated with verapamil (n = 10); (IV) diabetic group treated with nifedipine (n = 9);
(V) diabetic group treated with diltiazem (n = 10). Pellet diet supplemented with egg white and water was given ad libitum. Verapamil hydrochloride (25 mg/kg/day), diltiazem hydrochloride (30 mg/kg/day) and nifedipine (20 mg/kg/day) were initiated 72 h after streptozotocin injection. Verapamil and diltiazem were given in tap water; the bottles were covered with the alumunium foil in order to prevent sunlight contamination. Nifedipine was added to the powdered pellet diet supplemented with egg-white. At the end of 13weeks,all animals were sacrificed under ether anesthesia. Body weight, nonfasting blood glucose, glycated hemoglobin and total serum protein were measured. The determination of blood glucose, glycated hemoglobin
IV V
16’ 15** 22++* 12 16
l ****tP < 0.01. ***p < 0.05. $P < 0.001.
and total serum protein was done by the glucoseoxidase (Biotrol, France), thiobarbituric acid [ 141 and biuret-tartarate methods (Cyclova, Italy), respectively. For the statistical evaluation of body weight and blood glucose, Student’s r-test was used. Glycated hemoglobin (HbAi,) and total serum protein were evaluated by variance analysis [ 151. 3. Results The weights of healthy (control) animals increased significantly (P < O.Ol), whereas the diabetic animals lost weight (P c 0.01). The loss of weight in diabetic animals treated with diltiazem was significantly lower (P < 0.01) than that of the other diabetic groups, non-treated and treated with verapamil and nifedipine (Table 1). The non-fasting blood glucose levels of diabetic
Table 2 Pasma glucose levels (mean + SD.) Groups
n
Before treatment (mM/l)
After 13 weeks of treatment (mM/l)
I II III IV V
5 9 9 8 9
5.5 f 17 + 20 * 20 l 19 f
6.0 zt 21 + 20 f 20 f 20 l
l P < 0.05. **p < 0.001.
0.7 2.0; 2.0 2.0 2.0
l.O** 3.0*,** 3.0** 3.0** 3.0’.
A.A. Kaymaz et al. /Diabetes
Research and Clinical Practice 28 (1995) 201-205
Table 3 Glycated hemoglobin (HbA,,) and total serum protein levels at the end of 13 weeks (mean * SD.) Groups
n
HbA,, (%Hb)
Total protein (g/l)
I II III IV V
5 9 9 8 9
3.0 l 8.9 f 6.1 f 6.1 f 7.6 f
60 f 60 f 60 * 50 f 60*
****p
0.2’ 2.0**** 2.0*-•* 3.0. 2.0*
10 10 10 10 10
< 0.05.
animals increased slightly (P c 0.05) throughout the experiment, but the glycemic increments were not the same magnitude in the calcium channel blocker-treated groups as the diabetic ones (Table 2).
Glycated hemoglobin levels were significantly increased in all diabetic groups in comparison to the healthy control group (P < 0.001). In the diabetic group treated with verapamil, HbAt, levels were lower compared to the diabetic control group (P < 0.05) (Table 3), although the glycated hemoglobin levels were also high. There were no difference between the total serum proteins of all groups (Table 3). 4. Discussion Calcium channel blockers are used extensively in patients with cardiovasculer diseases,and these compounds have been thoroughly examined. Hass and Hartfelder reported, in 1962, that verapamil, a putative coronary vasodilatator, possessed negative inotropic and chronotropic effects [ 171. Fleckenstein and co-workers subsequently suggestedthat the negative inotropic effect resulted from inhibition of exitation-contraction coupling, and that the mechanism involved reduction of the movement of calcium ions into cardiac myocytes [ 171.The entry of extracellular calcium ions is more important in initiating the concentration of myocardial cells, while the release of calcium ions from intracellular storage sites also participates in vascular smooth muscle cells. The hydroxypyridines (one of the CCB family) may also inhibit cyclic nucleotide phosphodi-
203
esterases. The dual capacity of this drug to decreasecytosolic Ca2+ and to increase levels of cyclic nucleotide may contribute to their greater effects on vascular relaxation. The effects of these drugs on blood pressure, glycemic control and plasma lipids have been evaluated in several short-term studies dealing with a limited number of Type 2 diabetic patients [ 18,191.Most studies suggestthat calcium channel blockers do not have a clinically significant effect on glycemic control and plasma lipids. However, further long-term studies are required on the effect of calcium channel blockers in hypertensive diabetic patients. Chellingsworth et al. [20] reported that nifedipine significantly increases the blood sugar in comparison with verapamil and diltiazem in Type 2 diabetic hypertensive patients [ 13,20-221. Thus, Zezulka et al. [ 131reported that nifedipine, in doses ranging from 20 to 80 mg daily, in combination with thiazides, manifested three casesof overt diabetes mellitus out of 233 hypertensive patients within 3 weeks. Abasie and Passa[23], in their 3-month prospective, randomized, double blind, placebo-controlled study, reported no deleterious action of nifedipine on the fasting as well as postprandial glucose peak levels in 16 well-controlled diabetics with moderate untreated hypertension. A number of investigations has indicated that calcium ions play an important role in the genesis of long-term complications observed in tissues which are freely permeable to glucose such as liver, retina, blood vessels, kidney, central and peripheral nervous system [5,6,8,12]. Hightower et al. [5] reported that calcium deposition within the lens was influential in the genesisof cataract. As mentioned before, Chan and Junger [6] have found that Ca2+ entry across hepatocyte membrane increases in streptozotocin-diabetic rats. Mazzanti et al. [8] have shown that there is a positive correlation between the intraplatelet calcium levels and Ca2+-ATPaseactivity. On the other hand, there is some evidence demonstrating that intracellular calcium levels might be reduced by using calcium channel blockers [3,24]. Shiride and Robak [16] have demonstrated that verapamil has a strong inhibitory
204
A.A. Kaymaz et al. / Diabeies Research and Clinical Practice 28 (1995) 201-205
effect on lipid peroxidation, but nifedipine does not. Keyer Uysal and Kabasakal [25] have obtained similar results with nifedipine and diltiazem. In this study, at the end of 13 weeks, the average weights of all diabetic groups including calcium channel blocker-treated animals, were significantly lower than the average weight of the healthy control. However, there was a significant difference between the body weight of the diltiazem-treated diabetic group and that of other diabetic groups at the 13weeks(P < 0.01). We did not encounter any conclusive findings in terms of the effect of calcium channel blockers on body weight in the related medical literature. In diabetic animals, the non-fasting blood sugar levels were significantly higher at the end of the experiment than the initial levels. However, such an increment of blood glucose was not observed in animals treated with calcium channel blockers. In other words, the increase of glycemia in the calcium channel blocker-treated group was not of the same magnitude as in the streptozotocin-induced diabetic group. Although it has been reported that nifedipine might be diabetogenic [ 13,20,21,221, verapamil and diltiazem have no deleterious effects on blood glucose in Type 2 diabetic patients
Lw The glycated hemoglobin levels in all diabetic group were higher than those of controls. However, the levels of glycated hemoglobin in the verapamil-treated animals were slightly lower than that of other ones (P < 0.05). There is no published data concerning the effect of calcium channel blockers on glycated hemoglobin levels obtained from animal experiments or clinical observations. There are some data indicating that nifedipine has no adverseeffect on glycated hemoglobin concentration in patients with Type 2 diabetes mellitus WI.
It has also been shown that total serum protein levels were not affected in patients treated with calcium channel blockers [20]. As a conclusion, the findings obtained from this study suggestthat calcium channel blockers seem to have some beneficial effects on metabolic parametersof the mechanism of blood glucosecontrol in diabetic rats which are not treated with insulin.
Acknowledgements
We thank Dr. ilgin ijzden for his valuable advice during the experimental studying and Miss. Lale Tuncer for secretarial help. References
111Brownee,
M., Vlassara, H. and Cerami, A. (1987) The pathogenesis role of non-enzymatic glycosylation in diabetic complications. In: M.Y.C. Crabbe (Ed.), Diabetic Complications, Churchill Livingstone Press, Edinburgh, pp. 94-140. PI Dunbar, Y.C., Houser, F. and Levy, J. (1989) &Cell desensitization to glucose induced by hyperglycemia is augmented by increased calcium. Diabetes Res. Clin. Pratt. 7, 187-196. 131 Frey, M. and Fleckenstein, A. (1985) Die bedeutung der lenticularen calcium-uberladung fiir die cataractenstehung bei alloxan-diabetischen ratten. Fortschr. Ophthalmol. 82, 517-519. [41 Gronda, CM. and Gagliardo, Y.Y. (1988) Effect of different insulin secratagogues and blocking agents on islet cell Ca2+-ATPase activity. B&him. Biophys. Acta 943, 183- 189. 151Hightover, K.R, Leuerenz, V. and Reddy, V.N. (1980) Calcium transport in the lens. Invest. Ophthalmol. Vis. Sci. 19, 1059-1066. 161Chan, K.Y. and Junger, D. (1984) The effect of streptpzotocin-induced diabetes on the plasma membrane calcium uptake activity of rat liver. Diabetes 33, lO72- 1077. F.V. (1983) Calcium antagonists and 171 Defeudis, atherosclerosis-basic studies and therapeutic implications. Life Sci. 32, 557-563. 181Mazzanti, L., Rabini, R, Faloia, E., Fumelli, P., Bertoli, E. and De Pirro, R. (1980) Altered cellular Ca2+ and Na+ transport in diabetes mellitus. Diabetes 39, 850-854. 191 Kocak-Toker, N., Seckin, S., Sever, M. and Kocak, N. (1990) Erythrocyte lipid peroxidation and Ca2+-ATPase activity in chronic renal failure. Turk. J. Med. Biol. Res. I, 33-36. 1101Cruz, E. (1985) Reversal of diabetic cataract by sorbinil an aldose reductase inhibition. Diabetes 34, 14-21. 1111Liang, Y.N., Hershorin, L.L. and Chylack, L.T. (1986) Non-enzymatic glycations in human diabetic lens crystallins. Diabetologia 29, 225-228. 1121Perry, R.E., Swamy, M.S. and Abraham, E.C. (1987) Progressive changes lens crystallin glycation and highmolecular-weight aggreate formation leading to cataract development in streptozotocin-diabetic rats. Exp. Eye Res. 44, 269-282. [I31 Zezulka, A.V., Gill, J.S. and Beevers, D.G. (1984) Diabetogenic effects of nifedipine. Br. Med. J. 289, 438.
A.A. Kaymaz et al. /Diabetes
Research and Clinical Practice 28 (1995) 201-205
[l4] Fluckiger, R. and Winterhlalter, K.H. (1976) In vitro synthesis of HbAt,. FEBS Lett. 71, 356-360. [15] Senocak, M. (1990)Temel Bioistatik, Qglayan Kitabevi, Istanbul. 1161 Shiride, F. and Robak, J. (1988)The influence of calcium channel blockers on superoxide anions. Pharm. Res. Commun. 20, 13-21. [17] Murad, F. (1991)Drugs used for the treatment of angina: organic nitrates, calcium-channel blockers, and 8adrenergic antagonists. In: A.G. Gilman, T.W. Rail, A.S. Nies, P. Taylor (Eds.), Goodman and Gilman’s The Pharmacological Basis of Therapeutics, Pergamon Press, New York, pp. 764-783. [I81 Sruthers, A.D. (1985) The choice of antihypertensive therapy in the diabetic patient. Postgrad Med. J. 61, 563-569. [l9] Richie, C.M. and Atkinson, A.B. (1986) Towards better management of diabetic patient with raised blood pressure. Diabetic Med. 3. 301-305.
205
[20] Chellingsworth, M.C., Kendall, M.J., Wright, A.D., Pasi, S. and Pasi, J. (1989) The effects of verapamil, diltiazem, nifedipine and propranol on metabolic control in hypertensives with non-insulin dependet diabetes mellitus. J. Hum. Hypertension 3, 35-39. [21] Bhatnagar, S.K., Amin, M.H. and Al-Yusuf, A.R. (1984) Diabetogenic effects of nifedipine. Br. Med. J. 289, 19. [22] Charles, S., Ketelslegers, J.-M., Buysschaert, M. and Lambert, A.E. (1981) Diabetogenic effects of nifedipine. Br. Med. J. 283, 19-20. [23] Abasie, E. and Passa,P.H. (1984) Diabetogenic effects of nifedipine. (Letter) Br. Med. J. 289, 438. [24] Pierce, G.N., Afzal, N., Kroeger, E.A. et al. (1989)Cataract formation is prevented by administration of verapamil of diabetic rats. Endocrinology 125, 730-735. [25] Keyer-Uysal, M. and Kabasakal, L. (1990) The effect of lithium and calcium antagonists on brain lipid peroxide levels in mice. Euro. J. Pharmacol. 183, 2439.
ELSEVIER
The effects of calcium channel blockers, verapamil, nifedipine and diltiazem, on metabolic control in diabetic rats Alev Akdogan
Kaymaz*a, Hiiseyin Tana, Tuncay Altugb, A. Sevim Btiyi.ikdevrimb
“Department of Internal Medicine. Faculty of Veterinary Medicine, isranbul Universi[y, Avcilar 34851, Istanbul, Turkey blnstitute for Experimental Medical Research (DETAM), isranbul University, Istanbul, Turkey
Received 27 April 1993; revision received 2 May 1995;accepted 3 June 1995
Abstract The effects of calcium channel blockers (CCB)-verapamil, nifedipine, diltiazem on metabolic control in streptozotocin-induced long-term diabetes in rats were investigated. Diabetes mellitus was induced by single intravenous injection of streptozotocin (65 mgikg body wt.). The animals were divided into live groups: a healthy control group, a diabetic group and three diabetic groups treated with one of the calcium channel blockers (verapamil, 25 mg/kg/day, nifedipine, 20 mg/kg/day, and diltiazem, 30 mg/kg/day, respectively). Body weight, glycemia, glycated hemoglobin and total serum protein levels of these animals were measured at the beginning and at the end (after 13 weeks) of the experiment. It was observed that diabetic animals who were not treated with CCB had lost weight at the end of the experiment (P < 0.01). The blood glucose and glycated hemoglobin levels were increasedin the diabetic group in comparison to the healthy control group (P < 0.001). However, the calcium channel blockers seem to have beneficial effects on body weight, glycated hemoglobin and blood glucose levels. Keywmk
Calcium channel blockers; Diabetes mellitus; Streptozotocin; Metabolic control
1. Introduction
parallel
to the observation
mentioned
above,
Dunbar et al. [2] have observed that the 0 cell It has been shown that intracellular deposition of calcium increases in diabetic animals induced by streptozotocin [6]. It has also been reported that intracellular calcium levels of platelets [7,8] and erythrocytes [9] increased in streptozotocindiabetic rats. In addition to these findings, hyperglycemia inhibits Ca 2+-ATPase and increases intracellular calcium concentrations [l-5]. In l
Corresponding author.
desensitization to glucose induced by hyperglycemia is augmented by increased calcium levels within the islets. Gronda et al. [4] have reported that D-glucose shows inhibitory action on the Ca2+-ATPase activity of the plasma membranes of the pancreatic 0 cells. An alternative hypothesis is that glycated proteins which increase in diabetes bind higher amounts of calcium [lo- 131. Whether increase in intracellular calcium levels is a primary event
0168-8227/95/%09.500 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0168-8227(95)01090-Z
202
A.A. Kaymaz et al. /Diabetes
Research and Clinical Practice 28 (1995) 2OI-205
leading to complication, or an aftermath of increased non-enzymatic glycation, or both, is not clear yet. From this evidence, it seemsattractive to us to investigate the beneficial effects, if any, of different kinds of calcium channel blockers upon the metabolic control parameters in diabetic rats induced by streptozotocin.
Table 1 Body weights of the animals (mean i S.D.) Groups
n
Before treatmerit (g)
After 13 weeks of treatment (g)
I II
5 9 9 8 9
199 zt 192 f 199 f 191 f 199 f
310 l 15*q 147 l 27**-t,t 165 zt 30****$ 161 A 41$ 182 f 19tv$
III
2. Materials and methods Male Wistar albino rats, weighing approximately 200 g bred at the Institute for Experimental Medical Research (DETAM) of Istanbul University, were used. Diabetes mellitus was induced by a single intraveneous injection of streptozotocin in a dose of 65 mglkg body weight. Streptozotocin was dissolved in a citrate buffer at pH 4.5. The control group received only citrate buffer at the sameamount. The animals whose blood sugar levels were higher than 15 mM at the 48-h postinjection period were included in this study, and five experimental groups were established as follows: (I) healthy control group (n = 5); (II) diabetic group alone (n = 9); (III) diabetic group treated with verapamil (n = 10); (IV) diabetic group treated with nifedipine (n = 9);
(V) diabetic group treated with diltiazem (n = 10). Pellet diet supplemented with egg white and water was given ad libitum. Verapamil hydrochloride (25 mg/kg/day), diltiazem hydrochloride (30 mg/kg/day) and nifedipine (20 mg/kg/day) were initiated 72 h after streptozotocin injection. Verapamil and diltiazem were given in tap water; the bottles were covered with the alumunium foil in order to prevent sunlight contamination. Nifedipine was added to the powdered pellet diet supplemented with egg-white. At the end of 13weeks,all animals were sacrificed under ether anesthesia. Body weight, nonfasting blood glucose, glycated hemoglobin and total serum protein were measured. The determination of blood glucose, glycated hemoglobin
IV V
16’ 15** 22++* 12 16
l ****tP < 0.01. ***p < 0.05. $P < 0.001.
and total serum protein was done by the glucoseoxidase (Biotrol, France), thiobarbituric acid [ 141 and biuret-tartarate methods (Cyclova, Italy), respectively. For the statistical evaluation of body weight and blood glucose, Student’s r-test was used. Glycated hemoglobin (HbAi,) and total serum protein were evaluated by variance analysis [ 151. 3. Results The weights of healthy (control) animals increased significantly (P < O.Ol), whereas the diabetic animals lost weight (P c 0.01). The loss of weight in diabetic animals treated with diltiazem was significantly lower (P < 0.01) than that of the other diabetic groups, non-treated and treated with verapamil and nifedipine (Table 1). The non-fasting blood glucose levels of diabetic
Table 2 Pasma glucose levels (mean + SD.) Groups
n
Before treatment (mM/l)
After 13 weeks of treatment (mM/l)
I II III IV V
5 9 9 8 9
5.5 f 17 + 20 * 20 l 19 f
6.0 zt 21 + 20 f 20 f 20 l
l P < 0.05. **p < 0.001.
0.7 2.0; 2.0 2.0 2.0
l.O** 3.0*,** 3.0** 3.0** 3.0’.
A.A. Kaymaz et al. /Diabetes
Research and Clinical Practice 28 (1995) 201-205
Table 3 Glycated hemoglobin (HbA,,) and total serum protein levels at the end of 13 weeks (mean * SD.) Groups
n
HbA,, (%Hb)
Total protein (g/l)
I II III IV V
5 9 9 8 9
3.0 l 8.9 f 6.1 f 6.1 f 7.6 f
60 f 60 f 60 * 50 f 60*
****p
0.2’ 2.0**** 2.0*-•* 3.0. 2.0*
10 10 10 10 10
< 0.05.
animals increased slightly (P c 0.05) throughout the experiment, but the glycemic increments were not the same magnitude in the calcium channel blocker-treated groups as the diabetic ones (Table 2).
Glycated hemoglobin levels were significantly increased in all diabetic groups in comparison to the healthy control group (P < 0.001). In the diabetic group treated with verapamil, HbAt, levels were lower compared to the diabetic control group (P < 0.05) (Table 3), although the glycated hemoglobin levels were also high. There were no difference between the total serum proteins of all groups (Table 3). 4. Discussion Calcium channel blockers are used extensively in patients with cardiovasculer diseases,and these compounds have been thoroughly examined. Hass and Hartfelder reported, in 1962, that verapamil, a putative coronary vasodilatator, possessed negative inotropic and chronotropic effects [ 171. Fleckenstein and co-workers subsequently suggestedthat the negative inotropic effect resulted from inhibition of exitation-contraction coupling, and that the mechanism involved reduction of the movement of calcium ions into cardiac myocytes [ 171.The entry of extracellular calcium ions is more important in initiating the concentration of myocardial cells, while the release of calcium ions from intracellular storage sites also participates in vascular smooth muscle cells. The hydroxypyridines (one of the CCB family) may also inhibit cyclic nucleotide phosphodi-
203
esterases. The dual capacity of this drug to decreasecytosolic Ca2+ and to increase levels of cyclic nucleotide may contribute to their greater effects on vascular relaxation. The effects of these drugs on blood pressure, glycemic control and plasma lipids have been evaluated in several short-term studies dealing with a limited number of Type 2 diabetic patients [ 18,191.Most studies suggestthat calcium channel blockers do not have a clinically significant effect on glycemic control and plasma lipids. However, further long-term studies are required on the effect of calcium channel blockers in hypertensive diabetic patients. Chellingsworth et al. [20] reported that nifedipine significantly increases the blood sugar in comparison with verapamil and diltiazem in Type 2 diabetic hypertensive patients [ 13,20-221. Thus, Zezulka et al. [ 131reported that nifedipine, in doses ranging from 20 to 80 mg daily, in combination with thiazides, manifested three casesof overt diabetes mellitus out of 233 hypertensive patients within 3 weeks. Abasie and Passa[23], in their 3-month prospective, randomized, double blind, placebo-controlled study, reported no deleterious action of nifedipine on the fasting as well as postprandial glucose peak levels in 16 well-controlled diabetics with moderate untreated hypertension. A number of investigations has indicated that calcium ions play an important role in the genesis of long-term complications observed in tissues which are freely permeable to glucose such as liver, retina, blood vessels, kidney, central and peripheral nervous system [5,6,8,12]. Hightower et al. [5] reported that calcium deposition within the lens was influential in the genesisof cataract. As mentioned before, Chan and Junger [6] have found that Ca2+ entry across hepatocyte membrane increases in streptozotocin-diabetic rats. Mazzanti et al. [8] have shown that there is a positive correlation between the intraplatelet calcium levels and Ca2+-ATPaseactivity. On the other hand, there is some evidence demonstrating that intracellular calcium levels might be reduced by using calcium channel blockers [3,24]. Shiride and Robak [16] have demonstrated that verapamil has a strong inhibitory
204
A.A. Kaymaz et al. / Diabeies Research and Clinical Practice 28 (1995) 201-205
effect on lipid peroxidation, but nifedipine does not. Keyer Uysal and Kabasakal [25] have obtained similar results with nifedipine and diltiazem. In this study, at the end of 13 weeks, the average weights of all diabetic groups including calcium channel blocker-treated animals, were significantly lower than the average weight of the healthy control. However, there was a significant difference between the body weight of the diltiazem-treated diabetic group and that of other diabetic groups at the 13weeks(P < 0.01). We did not encounter any conclusive findings in terms of the effect of calcium channel blockers on body weight in the related medical literature. In diabetic animals, the non-fasting blood sugar levels were significantly higher at the end of the experiment than the initial levels. However, such an increment of blood glucose was not observed in animals treated with calcium channel blockers. In other words, the increase of glycemia in the calcium channel blocker-treated group was not of the same magnitude as in the streptozotocin-induced diabetic group. Although it has been reported that nifedipine might be diabetogenic [ 13,20,21,221, verapamil and diltiazem have no deleterious effects on blood glucose in Type 2 diabetic patients
Lw The glycated hemoglobin levels in all diabetic group were higher than those of controls. However, the levels of glycated hemoglobin in the verapamil-treated animals were slightly lower than that of other ones (P < 0.05). There is no published data concerning the effect of calcium channel blockers on glycated hemoglobin levels obtained from animal experiments or clinical observations. There are some data indicating that nifedipine has no adverseeffect on glycated hemoglobin concentration in patients with Type 2 diabetes mellitus WI.
It has also been shown that total serum protein levels were not affected in patients treated with calcium channel blockers [20]. As a conclusion, the findings obtained from this study suggestthat calcium channel blockers seem to have some beneficial effects on metabolic parametersof the mechanism of blood glucosecontrol in diabetic rats which are not treated with insulin.
Acknowledgements
We thank Dr. ilgin ijzden for his valuable advice during the experimental studying and Miss. Lale Tuncer for secretarial help. References
111Brownee,
M., Vlassara, H. and Cerami, A. (1987) The pathogenesis role of non-enzymatic glycosylation in diabetic complications. In: M.Y.C. Crabbe (Ed.), Diabetic Complications, Churchill Livingstone Press, Edinburgh, pp. 94-140. PI Dunbar, Y.C., Houser, F. and Levy, J. (1989) &Cell desensitization to glucose induced by hyperglycemia is augmented by increased calcium. Diabetes Res. Clin. Pratt. 7, 187-196. 131 Frey, M. and Fleckenstein, A. (1985) Die bedeutung der lenticularen calcium-uberladung fiir die cataractenstehung bei alloxan-diabetischen ratten. Fortschr. Ophthalmol. 82, 517-519. [41 Gronda, CM. and Gagliardo, Y.Y. (1988) Effect of different insulin secratagogues and blocking agents on islet cell Ca2+-ATPase activity. B&him. Biophys. Acta 943, 183- 189. 151Hightover, K.R, Leuerenz, V. and Reddy, V.N. (1980) Calcium transport in the lens. Invest. Ophthalmol. Vis. Sci. 19, 1059-1066. 161Chan, K.Y. and Junger, D. (1984) The effect of streptpzotocin-induced diabetes on the plasma membrane calcium uptake activity of rat liver. Diabetes 33, lO72- 1077. F.V. (1983) Calcium antagonists and 171 Defeudis, atherosclerosis-basic studies and therapeutic implications. Life Sci. 32, 557-563. 181Mazzanti, L., Rabini, R, Faloia, E., Fumelli, P., Bertoli, E. and De Pirro, R. (1980) Altered cellular Ca2+ and Na+ transport in diabetes mellitus. Diabetes 39, 850-854. 191 Kocak-Toker, N., Seckin, S., Sever, M. and Kocak, N. (1990) Erythrocyte lipid peroxidation and Ca2+-ATPase activity in chronic renal failure. Turk. J. Med. Biol. Res. I, 33-36. 1101Cruz, E. (1985) Reversal of diabetic cataract by sorbinil an aldose reductase inhibition. Diabetes 34, 14-21. 1111Liang, Y.N., Hershorin, L.L. and Chylack, L.T. (1986) Non-enzymatic glycations in human diabetic lens crystallins. Diabetologia 29, 225-228. 1121Perry, R.E., Swamy, M.S. and Abraham, E.C. (1987) Progressive changes lens crystallin glycation and highmolecular-weight aggreate formation leading to cataract development in streptozotocin-diabetic rats. Exp. Eye Res. 44, 269-282. [I31 Zezulka, A.V., Gill, J.S. and Beevers, D.G. (1984) Diabetogenic effects of nifedipine. Br. Med. J. 289, 438.
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