The pharmacology of a new oxytocic principle from ox hypothalamus.

1. An oxytocic substance has been isolated from ox hypothalamus by successive gel filtration on Sephadex G-25 and Sephadex G-50, and its pharmacology has been examined on three smooth muscle preparations.2. The substance has the same order of potency on rat uterus, guinea-pig ileum, and hen rectal caecum.3. The action of the substance on rat uterus was not abolished by thioglycollate.4. Atropine (1.0 mug/ml.), phenoxybenzamine (0.1 mug/ml.) and mepyramine (1.0 mug/ml.) did not block the smooth muscle action of the substance.5. Drug action, relative potency, and log dose-response relationships distinguish the substance from 5-hydroxytryptamine, acetylcholine, oxytocin, vasopressin, angiotensin amide, bradykinin, and purified preparations of substance P.