Effect of naloxone on the cardiovascular and sympathetic response to hypovolemic hypotension in the rat

Conscious rats were exposed to acute hypovolemic-hypotension by bleeding (5 ml/300 g body weight). Treatment with the opiate antagonist naloxone (7 mg/kg intra-arterial) following hemorrhage resulted in an increase of systolic blood pressure but not heart rate. Changes in plasma catecholamine levels did not differ between control and naloxone-treated animals. From these results we suggest that the ability of naloxone to improve blood pressure after hemorrhage is not due to increased sympatho-adrenomedullary activity.