Des-enkephalin-gamma-endorphin (DE gamma E): pharmacokinetics in dogs after intravenous and subcutaneous administration.

After intravenous dosing in dogs [3H-Lys9]-DE gamma E (Org 5878) was very rapidly eliminated from the circulation. Disappearance of the neuropeptide from blood followed a biphasic decay with half-lives of 0.6 +/- 0.1 min (+/- S.D.; alpha-phase) and 2.4 +/- 1.0 min (beta-phase). The central volume of distribution ranged between 0.05 and 0.23 l.kg-1. The mean blood clearance rate amounted to 0.15 l.min-1.kg-1, which is indicative of extensive hepatic and extrahepatic metabolism of DE gamma E. In contrast to intravenous dosing, subcutaneous injection of [3H]-DE gamma E in dogs resulted in low but relatively long-lasting peptide levels in blood. Peak values were found at 5-10 min, whereafter they declined to the limit of detection at 1.5-2 h. The bioavailability of DE gamma E for this route of administration was shown to be 20-23%.