The oxytocin-inactivating activity (OIA) of liver, kidney, uterus, pancreas, spleen and duodenum homogenates of hens was studied. The first-order constant of oxytocin inactivation was higher in the liver and pancreas than in the uterus and kidney or in the duodenum and spleen. Using synthetic analogues of oxytocin (deamino-oxytocin, deamino-carba1-oxytocin and carba1-oxytocin the mechanism of enzymic inactivation of oxytocin by hen tissue was investigated.
Enzymic hydrolysis by the CH2-terminal cleavage was most marked in duodenum (about 86% OIA) and kidney (54·8% OIA). Reduction of the disulphide bridge was most marked in the uterus (about 80% OIA) and pancreas (about 73% OIA). Splitting by non-specific aminopeptidases after reduction of the disulphide bridge occurred mainly in the liver (72% OIA) and in the spleen (44% OIA).