Naloxone reversal of hemorrhagic hypotension in the conscious guinea-pig is impeded by inhibition of the renin-angiotensin II system.

Naloxone reverses hemorrhagic hypotension in the conscious guinea-pig. Captopril and saralasin impede this naloxone effect, suggesting that angiotensin II is involved in naloxone action. This is compatible with previous work which has shown that B-endorphin inhibits the centrally mediated pressor action of angiotensin II, and that naloxone blocks this effect. Naloxone may be interacting with the postulated brain renin-angiotension II system or may be blocking the action of shock-induced circulating angiotensin II on a centrally located area such as the hypothalamus.