Naloxone reversal of insulin-induced hypotension in reserpine pretreated rats.

The administration of insulin caused a gradual lowering of systolic and diastolic blood pressure in anaesthetized reserpinized rats. Injection of 1 mg/kg naloxone at the peak of the hypotension resulted in immediate restoration of blood pressure to pre-insulin control values. The recovery of the arterial blood pressure caused by naloxone lasted for 5 to 10 min and was entirely dependent on the reserpine pretreatment. The lowering of the blood pressure caused by insulin and the increase in systemic blood pressure after naloxone were of about the same magnitude in rats with bilateral denervation of the adrenal glands as in sham operated rats. It is concluded that in anaesthetized reserpinized rats, hypoglycemia causes the release of opiate-like material that mediates a hypotensive response. The origin, nature and site of action of this opioid activity is as yet not established, but does not appear to derive from the adrenal gland.