Cardiovascular effects of chronic naloxone infusion in normal dogs.

It has now been established that there is an interaction between the cardiovascular control systems and opiate substances. To assess the role of endogenous opiates in the long-term control of blood pressure, the opiate antagonist naloxone (0.5 mg/kg/24 h) was infused intravenously for 7 days. Chronic blockade of endogenous opiates resulted in an elevation in arterial blood pressure which averaged 11% and was sustained throughout the infusion period. This was accompanied by a significant decrease in plasma renin activity averaging -59%. These data provide support for a tonic role of opioids in the long-term control of the cardiovascular system which may involve baroreceptor function.