Renal Excretion and Tissue Distribution of Radioactivity After Administration of Tritium-Labeled Oxytocin to Rats

Abstract

Renal excretion and tissue distribution of radioactivity after injection of oxytocin synthesized from tritium-labeled leucine were studied in anesthetized male rats. When 0.1–15 USP units was injected intravenously during water diuresis, about 30 to 35 % of the total radioactivity was excreted in a 2-hr period with more than half of this in the first 10 min. However, only about 10% of the total avian depressor activity was excreted. Paper chromatography suggested that the urine contained a mixture of unchanged oxytocin and at least 2 metabolic products also containing the tritium label. When 10 units of radioactive oxytocin was injected into normally hydrated rats and the animals were killed 20 min later by exsanguination, kidney, liver, adrenal gland and pituitary gland had a high concentration of radioactivity. The highest concentration was found in the kidney, almost 20 times that in the blood. Radioactivity was also detected in skeletal muscle and cerebral cortex, indicating the deep and generalized penetration of oxytocin and/or its radioactive metabolites into body tissues. (Endocrinology74: 226, 1964)