Oxytocin disappears rapidly from the circulation; half-lives in the circulation for the intravenously injected hormone of 40 sec. to 4 min. have been reported in a variety of species. In connexion with the interpretation of blood levels of oxytocin during suckling (Folley & Knaggs, 1966) the following experiments were carried out to determine the half-life of exogenous oxytocin in the circulation of the sow. Although the results are limited they may be worthy of report since no previous information for the sow is available.
Two experiments were performed on an adult sow (no. 2) weighing 102 kg. which had just lost a premature litter. In the first, the whole experiment was carried out while the sow was maintained under the anaesthetic (cyclopropane/oxygen) given for the insertion of a jugular cannula (for cannulation technique see Folley & Knaggs, 1966). One i.u. oxytocin (Pitocin, Parke, Davis and Co.) in 1 ml. 0·9%