VAGAL EFFERENT CONTROL OF ELECTRICAL-PROPERTIES OF THE HEART IN EXPERIMENTAL DIABETES

Autonomic neuropathy is a common and severe complication of diabetes m ellitus that leads to dysfunction of the cardiovascular system. The re duced ability to finely regulate heart rate is attributed to an impair ment of cardiac parasympathetic regulation, but it is not known whethe r this is due to parasympathetic neuropathy and/or direct cardiac impa irments. Therefore, we recorded the electrocardiogram of streptozotoci n-induced diabetic rats under basal conditions and during electrical s timulation of the vagus nerve. We used the neurotrophic agent Org 2766 , an adrenocorticotropic hormone [ACTH]-(4-9) analogue, to investigate the involvement of a neurogenic component in the altered vagal contro l of heart rate. The R-R interval was increased and atrioventricular t ransmission time unchanged 1 week after diabetes induction and remaine d so until 20 weeks. Treatment with Org 2766 could not prevent the bra dycardia, After bilateral vagotomy, both diabetic and non-diabetic rat s had the same R-R and P-R interval. The response of the R-R interval to electrical stimulation of the right vagus nerve was impaired, and t his impairment was not reversed by Org 2766 in diabetic rats. These re sults suggest that neurogenic factors are of little or no importance i n the impaired parasympathetic control of heart rate seen in experimen tal diabetes.