EFFECTS OF STREPTOZOTOCIN-INDUCED DIABETES ON HEART-RATE, BLOOD-PRESSURE AND CARDIAC AUTONOMIC NERVOUS CONTROL

Diabetes-associated alterations in resting heart rate and blood pressu re have been demonstrated in clinical studies and in animal models of insulin-dependent diabetes mellitus (IDDM). These alterations may resu lt from changes in the heart, vasculature or autonomic nervous system control. Using the streptozotocin-(STZ-) treated rat model of IDDM, th e current study was designed to: (1) monitor changes in heart rate and blood pressure continually during a 10-week period in conscious unres trained animals; and (2) determine if observed alterations in heart ra te were mediated by changes in sympathetic and/or parasympathetic nerv ous control. Biotelemetry techniques were used. Heart rate and blood p ressure were recorded 24 h a day at 10 min intervals before and after induction of diabetes. Diabetes was induced by i.v. administration of 50 mg/kg STZ. Resting autonomic nervous system tone was estimated by c hronotropic responses to full-blocking doses of nadolol (5 mg/kg i.p.) and atropine (10 mg/kg i.p.). STZ-induced diabetes was associated wit h time-dependent reductions in heart rate and its circadian variation. Diastolic blood pressure and mean arterial pressure did not differ si gnificantly when compared between control and STZ-treated animals; how ever, pulse pressure was diminished in diabetic rats. Chronotropic res ponses to both nadolol and atropine were blunted significantly in diab etic animals suggesting that resting levels of both vagal and sympathe tic nervous tone to the heart were diminished. Heart rate in the prese nce of both nadolol and atropine was also decreased in diabetic rats. All effects observed following administration of STZ were reversed, at least in part, by insulin treatment. These results suggest that IDDM is associated with time-dependent reductions in resting heart rare and autonomic nervous control of cardiac function. (C) 1998 Elsevier Scie nce B.V. All rights reserved.