Increased α1-adrenergic responsiveness of alloxan diabetic rat atria: effects of insulin therapy and thyroidectomy

Gen. Pharmac.Vol. 25, No. 3, pp. 559-564, 1994 Copyright © 1994 ElsevierScienceLtd Printed in Great Britain. All rights reserved 0306-3623/94 $7.00 + 0.00

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Increased l-Adrenergic Responsiveness of Alloxan Diabetic Rat Atria: Effects of Insulin Therapy and Thyroidectomy D I L E K L A F ( ~ I - E R O L , * V. M E L I H A L T A N , It a n d Y U S U F O Z T U R K 2 tAnkara University, Faculty of Pharmacy, Department of Pharmacology, 06100 Tandogan, Ankara and 2Anadolu University, Faculty of Pharmacy, Department of Pharmacology, 26470 Tepeba~i, Eski~ehir, Turkey

(Received 28 July 1993)

Abstract--l. Experimental models of diabetes are increasingly used for the investigation of cardiovascular complications as well as other complications due to diabetes mellitus. However, animal models have been used in relatively few studies on the myocardial ~-adrenergic responses. Hence, this report describes the effect of alloxan-induced diabetes and insulin-treatment on the ct~-adrenergic responses of the isolated rat atria. 2. Alloxan-induced diabetes caused an increase in the cq-adrenergic responses assessed in isolated spontaneoeusly beating rat atria. Both pD 2 and ~tE values for phenylephrine, an cq -adrenergic agonist were increased in atria from rats with alloxan diabetes. 3. Insulin treatment (4 IU/kg/day, s.c.) for 10 days normalized the changes in diabetic rat atria, pD 2 and ctE values for phenylephrine were slighly lower than those from control rats. Serum levels of thyroid hormones returned to normal following insulin trreatment as well. 4. The effect of insulin on the increased cq-adrenergic responses of rat atria due to alloxan diabetes seems to be related to thyroid hormone metabolism, since thyroidectomy also changed the atrial parameters measured. 5. The finding obtained in this study suggest that experimentally-induced diabetes increases cq -adrenergic sensitivity of the rat atria possibly due to an increased receptor affinity, but these changes can be reversed with insulin treatment.

Key words:Insulin, thyroidectomy, cardiovascular complications, spontaneously beating atria, ~-adrenoceptors, alloxan-diabetes, phenylephrine

INTRODUCTION Increased risk of cardiovascular disease is frequently encountered with diabetes mellitus (Fein and Sonnenblick, 1985). Cardiovascular diseases account for nearly 80% of all deaths in diabetic subjects (Cruickshanks et al., 1985; Kessler, 1971), and frequency of diabetic deaths, due to cardiovascular disease is 2 - 3 times higher than of the non-diabetic population (Kannel and McGee, 1979; Kannei et al., 1984). Autonomic neuropathy of the heart has been recognized as serious diabetic complication (Clarke et al., 1979; Fein and Sonnenblick, 1985; Thandroyen et al., 1980). Many investigators demonstrated a left ventricular dysfunction in diabetic patient that correlated with the duration and severity of diabetes

*Present address: 58 Rocky Point Road, Rock Point, NY 11778, U.S.A. "['To whom all correspondence should be addressed.

(Ahmed et al., 1975; Pittman et al., 1979; Shapiro et al., 1981). On the other hand, studies with experimentallyinduced diabetic animals revealed changes in isolated myocardial tissue function (Fein et al., 1981; Ojewole, 1985; Vadlamudi et al., 1982; Penpargkul et al., 1980; Rodrigues et al., 1988; Akiyama et al., 1989). Elevated ventricular basal development force and subsensitivity to the inotropic effects of isoproterenol has been reported (Ramanadham and Tenner, 1984; Ramanadham et al., 1987). This subsensitivity seems to be accompanied by the decreases in myocardial fl-adrenergic receptor density (Savarese and Berkowitz, 1979; Sundaresan et al., 1984). Relatively fewer studies have been conducted in relation to myocardial ~-adrenergic receptors due to experimental diabetes. Some investigators have demonstrated that a decrease in the number of cardiac ct-adrenergic receptors due to experimental diabetes (Heyliger et al., 1982; Williams et al., 1983; Latifpour and 559

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McNeill, 1984), while others have observed an increased ~l-adrenergic responsiveness in diabetic myocardium (Downing et al., 1983; Jackson et al., 1986; Lee et al., 1982). An increased responsiveness to methoxamine has been reported in 2 and 3 weeks diabetic lamps in vivo (Downing et al., 1983; Lee et al., 1982). It has also been reported that streptozotocin-induced diabetes causes an increase in rat left atrial responses to phenylephrine. The increase in the cq-adrenergic responsiveness has been attributed to the changes in intracellular calcium mobilization of the myocardium as a consequence of experimentallyinduced diabetes (Jackson et al., 1986). The effect of insulin treatment on the diabetes-induced changes in myocardial cq-adrenergic responses has not been investigated yet. Hence, the present study was undertaken to investigate the effect of insulin replacement therapy on the diabetic changes in the myocardial Ctl-adrenergic receptors using alloxan-diabetic rats. The possible role of thyroid hormones in the effect of insulin on the diabetic changes in myocardial ~q-adrenergic responsiveness was also examined. MATERIALS AND M E T H O D S Animals

Male Wistar rats (230-300 g) from a local strain were used. Rats were housed in a room with controlled temperature (21 _+2°C) and humidity (65-70%) care being taken of the day and night cycle. The rats were divided into five groups and housed separately in metabolic cages: group 1, control; group 2, alloxan-diabetic; group 3, insulintreated diabetic; group 4, thyroidectomized diabetic; group 5, thyroidectomized insulin-treated diabetic rats. During the experiments, all the animals had free access to food and water. Diabetes was induced by a single injection of alloxan in ice-cold saline (60 mg/kg body weight) directly into the dorsal tail vein. The injection volume did not exceed 0.1 ml. On the other hand, 5 weeks after the diabetes induction, the rats in the 3rd group were given insulin (4 IU/kg/day s.c.) for 10 days. Surgically thyroidectomized rats were given alloxan (60mg/kg, i.v.) 10 days after the surgery (group 4). Five weeks after the alloxan injection, some of the thyroidectomized diabetic rats were treated with insulin (4 IU/kg/day s.c.) for 10 days (group 5). Body weights were obtained before treatment and prior to killing. Blood samples were collected from the tail vein at the time of killing and blood glucose levels were determined by glucose oxidase enzymatic assay (Glucometer, Ames, U.S.A.). Plasma T 3 and T4 levels were measured by radioimmunoassay using

commercial kits purchased from DPC, Diagnostic Products Corporation (Los Angeles, U.S.A.). Isolation o f tissue

After 5 weeks diabetes plus 10 days insulin treatment, the rats were killed by a blow on the head and their hearts quickly removed and placed in ice-cold saline. Spontaneously beating atria were prepared according to the method described by Foy and Lucas (1978) with minor modifications (Karasu et al., 1990; Oztfirk et al., 1993a, b). The atria were carefully dissected from the ventricles and remaining nonatrial tissue. One of the atria was connected to a tissue holder and another to an isometric force transducer (Ugo Basile, No. 7005), recording on an Ugo Basile microdynamometer (No. 7050), the preparation being set up in a 10-ml organ bath containing physiological saline of the following composition (mM): NaCI 117, KC14.7, CaCI2.6H20 2.5, KH2PO 4 1.2, MgSO4"7H20 1.2, NaHCO 3 22.3 and dextrose 5.6. The physiological solution was maintained at 34°C, pH 7.4 and oxygenated with 95% 02 and 5% CO2. The atria were subjected to a resting tension of 0.5 g and allowed to equilibrate to 60 min, while the incubation fluid was changed every 15 min. After this initial incubation, the basal inotropic and chronotropic responses of atria were measured. Phenylephrine was then added into the organ bath in order to obtain non-cumulative dose-response curves. Contractile responses of the spontaneously beating atria were magnified 8-fold in all cases. Data analysis and statistics

All measurements of changes in contractility and heart rate in response to phenylephrine were calculated in percentage changes. Basal contractility of spontaneously beating atria were expressed as mg of isometric contractions, pD 2 and ~E values which are apparent affinity constant of agonist and intrinsic activity respectively were calculated to evaluate the action of phenylephrine on the atria isolated from non-diabetic, diabetic, insulin-treated diabetic, thyroidectomized-diabetic and insulintreated-thyroidectomized-diabetic rats. pD2 value is the negative logarithm of the phenylephrine concentration which produces 50% of maximal responses, i.e. pD, = -log(ECs0). In the calculation of pD2, percent inotropic responses to phenylephrine were used. The method for the calculation of ~E for the non-diabetic rat atria was that the maximal responses to phenylephrine on non-diabetic atria were accepted 1.00, i.e. ~E= 1.00 and other ~E values for the atria in the pathophysiological conditions mentioned were derived by rationing of maximal response of nondiabetic rat atria to others, i.e. ct = EAm/EA, m. EAm

Effects of insulin therapy and thyroidectomy Table I. Changes in the body weight and blood glucose levels of normal (C), alloxan-diabetic(DIA), insulin-treateddiabetic (DIA + INS), thyroidectomizeddiabetic (DIA + THY) and insulin-treated thyroidectomizeddiabetic (DIA + GLY + INS) rats (values refer to mean ___SEM in each group, n = experiment number) Group

n

C DIA DIA + INS DIA + THY DIA + THY + INS

8 8 7 10 6

Body weight (g)

Blood glucose (mg/100 ml)

255.00_+5.30 140.56 _+2.69* 249.29 _+2.80 226.66 _+3.89 134.28-+5.67"

115.50_+2.79 369.00 _+5.09* 125.42 _+3.27 375.28 + 6.24* 116.28-+1.43

*Statistical significanceP < 0.005 relative to control rats. and EA,m are the maximal responses to phenylephrine o f non-diabetic atria and o f the atria obtained from other experimental groups, respectively (Ariens and Van Rossum, 1957; Ariens and Simonis, 1964). Results are expressed as means + SEM (standard error o f mean). Sensitivity o f the tissues to the phenylephrine was analysed by A N O V A (One-way variance analysis) with an IBM PS/2 (Model80)

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Table 3. Basal inotropic and chronotropic responsesof spontaneously beatingatria from normal (C), alloxan-diabetic(DIA), insulintreated diabetic (DIA + INS), thyroidectomizeddiabetic (DIA + THY) and thyroidectomizedinsulin-treated diabetic (DIA + THY + INS) rats (values refer to mean_+SEM in each group, n = experiment number) Basal contractility Basalh e a r t r a t e Group n (mg) (beat/min) C 9 322.19+ 13.64 239.20 + 8.20 DIA 8 812.41 + 45.39* 123.00 _+ 12.00" DIA + INS 7 216.63+ 22.35 232.30 + 6.60 DIA + THY 10 716.59+ 64.82* 122.33 + 12.00" DIA + THY + INS 6 605.49+ 29.07* 125.20 _+ 15.00* aStatistical significanceP < 0.005 relative to controls. ineffective on the blood glucose levels o f alloxandiabetic rats. On the other hand, plasma levels o f thyroid h o r m o n e s were significantly reduced in alloxan-treated rats (Table 2). Nevertheless, insulin administration to alloxan diabetic rats increased the concentrations o f thyroid h o r m o n e s toward the levels found in control rats (Table 2).

c o m p u t e r using S T A T G R A F R p r o g r a m which was developed by Statistical Graphics Corp.

Spontaneously beating rat atria

Drugs used

found to be significantly decreased when c o m p a r e d to those obtained from control animals. Furthermore, an enhanced basal contractility was observed in the

Alloxan m o n o h y d r a t e and phenylephrine hydrochloride were purchased from Sigma Chemical Co., St Louis, Mo., U.S.A. Insulin N P H was obtained from Organon, Turkey.

The basal rate o f contractility o f diabetic atria was

atria isolated from alloxan-diabetic rats relative to those from control animals. Insulin-treated rats did not exhibit any such changes (Table 3). However, insulin was found to be ineffective when administered

RESULTS

Induction of experimental diabetes In the present study, 24-48 hr after alloxan-treatment, rats d e m o n s t r a t e d characteristic s y m p t o m s o f diabetes such as polyphagia, polydipsia, weight loss, stable hyperglycaemia, reduced thyroid h o r m o n e levels etc. Body weight measurements before treatment and prior to sacrifice revealed a significant decrease in the body weight o f alloxan-treated rats

to thyroidectomized diabetic rats. When chronotropic responses to phenylephrine were examined the absolute rates obtained in diabetic atria to this agent were found to be significantly increased at each dose employed (P < 0.005) (Fig. 1). Similarly, diabetic atria were found to possess diminished responsiveness to inotropic effect of phenylephrine (P < 0.005) (Fig. 2). Insulin treatment o f

relative to controls. Furthermore, blood glucose determinations indicated a significant hyperglycaemia in alloxan-treated rats when c o m p a r e d to nondiabetic and insulin treated diabetic animals. Table 1 summarizes the mean + SEM changes in body weight and blood glucose levels 5 weeks after alloxan treatment. The results shown in Table 1 also indicate the insulin treatment with or without thyroidectomy reversed the alterations in blood glucose levels due to experimental diabetes, while thyroidectomy itself was Table 2. Serum thyroid hormone levels from normal (C), alloxandiabetic (DIA) and insulin-treateddiabetic (DIA + INS) rats (values refer to mean + SEM in each group, n = experiment number) Group

n

C DIA DIA + INS

8 8 7

T3 (ng/100 ml) 104.68 + 12.63 35.81 + 4.66* 93.40 + 14.31"

c DIA D1A+INS

350 300

-

~ 250 200 0~ 150 100

50 0 6

5

4

T4 (/~g/100 ml)

-log (M) Phenylephrine concentration

4.56 + 0.17 1.44 + 0.27* 4.43 _+0.19

Fig. 1. Chronotropic responses to phenylephrine of the spontaneously beating atria from normal (C), alloxandiabetic (DIA) and insulin-treated diabetic (DIA + INS) rats (values refer to mean + SEM in each group).

*Statistical significance P < 0,01 relative to controls.

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DILEK LAF~;I-EROL et al.

J[ / 100

Ilc []

Ii DIA

[]

DIA+INS

[]

DIA+THY

i

I

¢~

80-

.=_

40 2o

=

"0

6

5

4

-log (M) Phenylephrine concentration Fig. 2. lnotropic responses to phenylephrine of the spontaneously beating atria from normal (C), allo×an-diabetic (DIA), insulin-treated diabetic (DIA + INS), thyroidectomized diabetic (DIA+THY) and thyroidectomized insulin-treated diabetic (DIA + THY + INS) rats (values refer to mean + SEM in each group). alloxan-diabetic rats for 10 days normalized the inotropic (Fig. 2) but not chronotropic (Fig. 1) responsiveness of diabetic rat atria to this agent. In contrast, insulin did not restore the inotropic responsiveness of atria to phenylephrine when administered to thyroidectomized diabetic rats (Fig. 2). The results in Table 4 demonstrate PD2 (apparent affinity constant of agonist) and ctE (intrinsic affinity) values for inotropic responses to phenylephrine in normal and diabetic atria. As seen in the table, both pD 2 and a E values for phenylephrine were increased in diabetic rat atria. Insulin administration to diabetic rats reduced the pD 2 value near the level found in control animals while ~E value following insulin treatment was lower than that obtained from control animals, pD 2 and ctE values obtained from thryoidectomized insulin-treated diabetic rats were significantly higher than obtained from controls, while ct E value was in the same magnitude as in control rats. DISCUSSION The results of the present study clearly indicate that aUoxan-induced diabetes causes an increase in the Table 4. pD 2 and ctE values concerning inotropic responses to phenylephrine of spontaneously beating atria from normal (C), alloxandiabetic (DIA), insulin-treated diabetic (DIA + INS), thyroidectomized diabetic (DIA + THY) and thyroidectomized insulin-treated diabetic (DIA + THY + INS) rats (values refer to mean ± SEM in each group, n = experiment number) Group

n

C DIA DIA + INS DIA + T H Y DIA + THY + INS

9 8 6 6 6

pD 2 5.36 ± 6.19 ± 5.16 ± 6.17 ± 5.64 +

0.05 0.05 ~ 0.06 0.05 ~ 0.05 ~

~tE 1.00 ± 1.22 ± 0.77 ± 1.21 + 1.02 ±

"Statistical difference P < 0.005 relative to diabetic rats.

0.03 0.04 a 0.06 0.04" 0.04"

a,-adrenergic responsiveness of the spontaneously beating rat atria. Since pD2 values for phenylephrine are significantly increased in the diabetic rat atria, increased ctt-adrenergic responsiveness in this tissue may be attributed to an increased affinity of myocardial ctt-adrenergic receptors. Disease is an important factor known to affect the pharmacodynamics of drugs and endogenous substances. The pathophysiology of experimental diabetes in animals has been discussed earlier (Bell and Hye, 1983). Moreover, increased ~q-adrenergic responses has been reported as a diabetic complication. Augmented contractile response to norepinephrine has been indicated in streptozotocin-diabetic rats (Peredo et al., 1983; Peredo and Borda, 1985). This observation, however, has not been confirmed in the vas deferens from spontaneously diabetic BB rats (Longhurst, 1991). Tail ventral artery and portal vein from alloxandiabetic rats also exhibit an increased contractility in response to norepinephrine (Fiol de Cunco et al., 1988). Increased myocardial cq-adrenergic responsiveness has also been observed in experimentally diabetic animals (Downing et al., 1983; Jackson et al., 1986; Lee et al., 1982). Decreased number of ~-adrenergic receptors in myocardium seems to accompany the increased cq-adrenergic responsiveness (Heyliger et al., 1982; Williams et al., 1983; Latifpour and McNeill, 1984). The physiological role of cq-adrenergic receptors in the myocardium has not been fully understood (Manning and Hearse, 1984; Fedida et al., 1993). It has been long-known that ctl-adrenergic stimulation causes a positive inotropic effect in the myocardium (Benley and Varma, 1967; Govier, 1967). Under certain pathological circumstances, such as ischemia-induced arrhythmias, chronical failure of myocardium, hyperthyroidism, diabetes etc. (Rosen et al., 1991). cq-Adrenergic receptors have been suggested to play an important role for the regulation of myocardial function. On the other hand, it has been demonstrated that fl-adrenergic responsiveness of the atria is decreased both in insulin-dependent (Savarese and Berkowitz, 1979; Karasu et al., 1990; 0ztfirk et al., 1993) and in non-insulin-dependent (Oziiart et al., 1993) diabetic rats. Therefore, it seems likely that the augmented ~q-adrenergic responses observed in this study may serve as a compensatory mechanism to restore overall responsiveness of diabetic rat myocardium to endogenous catecholamines. According to the findings obtained in the present study, insulin treatment reverses the diabetic changes in both basal and phenylephrine-induced contractility of the rat atria. It has been observed that insulin treatment also improves the decreased fl-adrenergic responses of the spontaneously beating atria

Effects of insulin therapy and thyroidectomy (Karasu et al., 1990; Ozt/irk et al., 1993). The role o f the thyroid h o r m o n e s in the effect o f insulin on the diabetic rat atria is not understood, since thyroidectomy exerted diverse effects on the experimental conditions examined in the present study. Acknowledgement--Authors are grateful to Professor K. H. C. Ba~er, Director of Medicinal Plant Research Center in Eski~ehir, for the computer facilities used in this study.

REFERENCES Ahmed S. S., Jaferi G. A., Narung R. M. and Regan J. J. (1975) Preclinical abnormality of left ventricular function in diabetes mellitus. Am. Heart J. 89, 153-158. Akiyama N., Okumura K., Watanabe Y., Hashimoto H., Ito T., Ogawa K. and Satake T. (1989) Altered acetylcholine and norepinephrine concentrations in diabetic rat heart. Role of parasympathetic nervous system in diabetic cardiomyopathy. Diabetes 38, 231 236. Ariens E. J. and Simonis A. M. (1964) Drug receptor interaction: interaction of one or more drugs with a receptor system. In Molecular Pharmacology (Edited by Ariens E. J.), Vol. 1, pp. I19-286. Academic Press, London. Ariens E. J. and Van Rossum J. M. (1957) pDx, pA,. and pD~ values in analysis of pharmacodynamics. Arch. int. Pharmaeodyn. 110, 275-299. Bell R. J. and Hye R. H. (1983) Animal models of diabetes mellitus: physiology and pathology. J. Surg. Res. 35, 433 460. Benfey B. G. and Varma D. R. (1967) Interactions of sympathomimetic drugs, propranolol and phentolamine on atrial refractory period and contractility. Br. J. Pharmac. 30, 603-611. Clarke B. F., Ewing D. J. and Campbell J. W. (1979) Diabetic autonomic neuropathy. Diabetologia 17, 195-212. Cruickshanks K. J., Orchard T. J. and Becker D. J. (1985) The cardiovascular risk profile of adolescents' insulin-dependent diabetes mellitus. Diabetes Care 8, 118 124. Downing S. E., Lee J. C. and Fripp R. R. (1983) Enhanced sensitivity of diabetic hearts to ~t-adrenoceptor stimulation. Am. J. Physiol. 245, H808 H813. Fedida D., Braun A. P. and Giles W. R. (1993) a t-Adrenoceptors in myocardium: functional aspects and transmembrane signaling mechanism. Physiol. Rev. 73, 469-487. Fein F. S., Strobeck J. E., Malhotra A., Scheuer J. and Sonnenblick E. H. (1981) Reversibility of diabetic cardiomyopathy with insulin in rats. Circ. Res. 49, 1251 1261. Fein F. S. and Sonnenblick E. H. (1985) Diabetic cardiomyopathy. Prog. Cardiovasc. Dis. 27, 255-271. Fiol de Cunco M., Ruiz R. D., Lacuara J. L. and Santillian de Torres R. (1988) Contractility and pharmacological reactivity of isolated vascular smooth muscle from diabetic rats. Pharmacology 36, 228 237. Foy J. M. and Lucas P. D. (1978) Comparison between spontaneously beating atria from control and streptozotocin-diabetic rats. J. Pharm. Pharmac. 30, 558 562. Govier W. C. (1967) A positive inotropic effect of phenylephrine mediated through alpha-adrenergic receptors. L(fi" Sei. 6, 1361. Heyliger C. E., Pierce G. N., Singal P. K. and Dhalla N. S. (1982) Cardiac alpha- and beta-adrenergic receptor alterations in diabetic cardiomyopathy. Basic Res. Cardiol. 77, 610-618. Jackson C. V., McGrath G. and McNeill J. H. (1986) Alteration of alpha-I adrenoceptor stimulation in the

563

experimental diabetic rat myocardium. Can. J. Physiol. Pharmac. 64, 145 151. Kannel W. B. and McGee D. L. (1979) Diabetes and cardiovascular disease: the Framingham study. J. Am. med, Ass. 241, 2035 2038. Kannel W. B., Hjortland M. and Castelli W. (1984) Role of diabetes in congestive heart failure: the Framingham study. Am. J. Cardiol. 34, 29 34. Karasu t~., Oztfirk Y., Altan N., Yfl&zo~lu-An N., Ikizler C. and Altan V. M. (1990) Thyroid hormones mediated effect of insulin on alloxan diabetic rat atria. Gen. Pharmae. 21, 735-740. Kessler 1. (1971) Mortality experience of diabetic patients. Am. J. Med. 51, 715-724. Latifpour J. and McNeill J. H. (1984) Cardiac autonomic receptors: Effect of long-term experimental diabetes. J. Pharmac. exp. Ther. 230, 242-249. Lee J. C., Fripp R. R. and Downing S. S. (1982) Myocardial responses to alpha adrenoceptor stimulation with methoxamine hydrochloride in lambs. Am. J. Physiol. 242, H405-H410. Longhurst P. A. (1991) In vitro contractile responses of vasa deferentia from spontaneously diabetic BB rats. J. Auton. Pharmac. 11, 63-71. Manning A. S. and Hearse D. J. (1984) Reperfusion-induced arrhythmias. Mechanisms and prevention. J. molec. Cell. Cardiol. 16, 497-518. Ojewole J. A. O. (1985) The influence of streptozotocininduced diabetes on myocardial contractile performance in vitro. Meth. Find. Exp. Clin. Pharmac. 7, 119-125. C)ztfirk Y., Yddlzo~lu-Arl N., Altan V. M. and t3zqelikay A. T. (1993a) Effect of insulin on the decreased /~-adrenergic responses of duodenum and atrium isolated from streptozotocin-diabetic rats. Gen. Pharmac. 24, 217-223. Oziian A., Oztfik Y., Yddlzo~lu-Arl N., Ozqelikay A. T. and Altan V. M. (1993b) The effects of glyburide and insulin on the cardiac performance in rats with noninsulin-dependent diabetes mellitus. Gen. Pharmac. 24, 165 169. Penpargkul S., Schaible T., Yipitsoi T. and Scheuer J. (1980) The effect of diabetes on performance and metabolism of rat hearts. Circ. Res. 47, 911-921. Peredo H. and Borda E. (1985) The effects of norepinephrine and acetylcholine in the rat vas deferens from normal and diabetic rats: influence of ouabain and verapamil. Meth. Find. Exp. Clin. Pharmac. 7, 573-577. Peredo H., Agostini M. D. C., Gimeno M. F. and Borda E. (1984) Hypersensitivity to norepinephrine in vasa deferentia from diabetic rats. Possible participation of metabolic products of arachidonic acid. Prostaglandins Leukotriens Med. 15, 229 239. Pittman C. S., Suda A. K., Chambers J. B. Jr, McDaniel H. G., Ray G. Y. and Pretson B. K. (1979) Abnormalities of thyroid hormones turnover in patients with diabetes mellitus, before and after insulin therapy. J. Clin. Endocr. Metab. 48, 854-860. Ramanadham S. and Tenner T. E. Jr (1984) Basal development force and inotropic characteristics of myocardial tissue isolated from streptozotocin-diabetic animals. Proc. West. Pharmae. Soe. 276, 197-200. Ramanadham S., Young J. and Tenner T. E. Jr (1987) Prevention of streptozotocin-induced alterations in the rat heart by 3-o-methylglucose and insulin treatments. J. Cardiovasc. Pharmac, 9, 291 297. Rodrigues B., Xiang H. and McNeill J. H. (1988) Effect of L-carnitine treatment on lipid metabolism and cardiac performance in chronically diabetic rats. Diabetes 37, 1358-1363. Rosen M. R., Anyukhovsky E. P. and Steinberg S. F. (1991) :~-Adrenergic modulation of cardiac rhythm. News Physiol. Sei, 6, 134 1138.

564

DILEK LAF(~I-EROLet al.

Savarese J. J. and Berkowitz B. A. (1979) fl-Adrenergic receptor decrease in diabetic rat hearts. Life Sci. 25, 2075-2078. Shapiro L. M., Leatherdale B. A., MacKinnon J. and Fletcher R. F. (1981) Left ventricular function in diabetes mellitus: II. Relation between clinical features and left ventricular function. Br. Heart J. 45, 129-132. Sundaresan P. R., Sharma V. K., Gingold S. L. and Banerjee P. S. (1984) Decreased beta-adrenergic receptors in rat heart in streptozotocin-induced diabetes: role of thyroid hormones. Endocrinology 114, 1358-1363. Thandroyen F. J., Asmal A. C., Bhagat C. I. and Dayal B, (1980) Autonomic neuropathy in non-insulin-

dependent diabetes mellitus in young. S. Aft. reed. J. 58, 55-57. Uusitupa M., Siitonen O., Aro A., Korhonen T. and Py6rhl/i K. (1983) Effect of correction of hyperglycemia on left ventricular function in non-insulin-dependent (type 2) diabetics. Acta rned. scan. 213, 363-368. Vadlamudi R. V. S. V., Rodgers R. L. and McNeill J. H. (1982) The effect of chronic alloxan- and streptozotocininduced diabetes on isolated rat heart performance. Can. J. Physiol. Pharmac. 60, 902-911. Williams R. S., Schaible T. F., Scheuer J. and Kennedy R. (1983) Effects of experimental diabetes on adrenergic and cholinergic receptors of rat myocardium. Diabetes 32, 881-886.