Effects of streptozotocin-induced diabetes on heart rate, blood pressure and cardiac autonomic nervous control.

Diabetes-associated alterations in resting heart rate and blood pressure have been demonstrated in clinical studies and in animal models of insulin-dependent diabetes mellitus (IDDM). These alterations may result from changes in the heart, vasculature or autonomic nervous system control. Using the streptozotocin- (STZ-) treated rat model of IDDM, the current study was designed to: (1) monitor changes in heart rate and blood pressure continually during a 10-week period in conscious unrestrained animals; and (2) determine if observed alterations in heart rate were mediated by changes in sympathetic and/or parasympathetic nervous control. Biotelemetry techniques were used. Heart rate and blood pressure 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 chronotropic responses to full-blocking doses of nadolol (5 mg/kg i.p.) and atropine (10 mg/kg i.p.). STZ-induced diabetes was associated with time-dependent reductions in heart rate and its circadian variation. Diastolic blood pressure and mean arterial pressure did not differ significantly when compared between control and STZ-treated animals; however, pulse pressure was diminished in diabetic rats. Chronotropic responses to both nadolol and atropine were blunted significantly in diabetic animals suggesting that resting levels of both vagal and sympathetic nervous tone to the heart were diminished. Heart rate in the presence 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 rate and autonomic nervous control of cardiac function.