Circulating dopamine levels and a protective action of naloxone in canine splanchnic arterial occlusion shock.

The possible beneficial actions of naloxone (NAL) were evaluated in canine splanchnic arterial occlusion (SAO). MEan arterial pressure (MAP), cardiac output (CO) and left ventricular contractility (LV dP/dt max) were measured in pentobarbital anesthetized dogs. Animals received intravenously NAL (8 mg/kg) or an equivalent volume of 0.9% saline prior to occlusion or sham occlusion, followed by infusion of 8 mg/kg/hr. The occlusion was released after 2 hr and the dogs monitored for an additional 3 hr or until MAP fell to 40 mmHg. Blood was drawn during the experiments for analysis of dopamine (DA), norepinephrine (NE) and epinephrine (E). SAO and SAO + NAL dogs had decreased MAP and CO after release. However, SAO + NAL animals had a higher LV dP/dt max. NAL in sham and SAO dogs produced significantly higher plasma DA and E levels than in their respective control groups. 67% of SAO + NAL survived 3 hr post release, compared to 43% of SAO dogs. Although the mechanism of NAL protection remains undefined, it may relate to altered vascular response to endogenous opiates or catecholamines.