Alterations in the baroreceptor reflex control of heart rate in streptozotocin diabetic rats

Baroreflex control of heart rate was studied in conscious diabetic rats at 12, 24 and 48 weeks after the induction of diabetes with streptozotocin. Baseline blood pressure (mean arterial blood pressure) of diabetic rats was significantly lower at 12 weeks after the induction of diabetes when compared to age-matched control rats. However, at 24 and 48 weeks of diabetes, no difference in blood pressure was observed between diabetic and age-matched control rats. In contrast, bradycardia (prolongation of pulse interval) was a consistent feature of diabetic rats at all time points (12, 24, and 48 weeks). To assess parasympathetic control of heart rate, baroreceptor sensitivity was determined by infusing phenylephrine. Baroreflexes in diabetic rats were changed from an increased sensitivity at 12 and 24 weeks to decreased sensitivity at 48 weeks after the induction of diabetes. This suggests that alterations in baroreflex sensitivity might depend upon the length of time the animals were exposed to the diabetes. Insulin treatment in diabetic animals reversed hypotension, bradycardia and altered baroreflex sensitivity observed in 12-week diabetic rats. Non-diabetic rats, in which the development of diabetes was prevented by pretreatment with 3-0-methylglucose before streptozotocin injection, or rats which did not develop diabetes after streptozotocin injection showed a similar baseline blood pressure, heart rate and baroreflex sensitivity to those of age-matched control rats (12, 24 and 48 weeks). This data suggests that changes in blood pressure, heart rate and baroreflex sensitivity are due to the diabetic state, not to streptozotocin toxicity.