Tissue uptake of 3H-naloxone in control and in hemorrhagic shock cats

Tissue uptake and plasma levels of 3H-naloxone were studied in normotensive control cats, as well as in hemorrhagic hypotensive cats. Intravenous injection of naloxone resulted in a rapid and extensive uptake of naloxone label from plasma by several tissues. Plasma half-life of the radiolabel was determined to be 137 min. One and two hours after injection, large amounts of naloxone label were found in the liver, pancreas, adrenal, kidney and lung, with tissue/plasma ratios ranging from 2 to 30. Brain tissue displayed the lowest tissue/plasma ratios of any organ sampled. Infusion of 8 mg/kg -1.hr-1 naloxone resulted in an increase in concentration of radiolabel over a 2 hr period. Hemorrhagic shock did not significantly retard uptake of naloxone by tissues. Splanchnic organs displayed high uptake of naloxone even during hemorrhagic shock. Brain tissue in cats subjected to hemorrhagic shock had the lowest uptake naloxone of all tissues sampled. The degree of uptake of naloxone by tissues is consistent with its proposed role in lysosomal membrane stabilization and prevention of proteolysis during hemorrhagic shock.