. Introduction
The placenta, which produces many hormones, is not known to produce oxytocin. This hormone is produced in the posterior pituitary and primarily responsible for uterine contraction claimed that she uses powdered dried sheep placenta, administered orally, to facilitate delivery in patients with uterine inertia.Sisson et al. (1961) have shown that dialysates from homogenates of rabbit placenta contain ahypotensive-inducing, smooth muscle contracting principle, which was later shown by Sisson (1963) to be a polypeptide which was not oxytocin or bradykinin. The substance, however, did not contract the gravid rabbit uterus.Even if the sheep placenta produced an oxytocic peptide, it would seem unreasonable to assume that the dried placenta could contain an active oxytocic peptide. Nonetheless, it was decided to investigate the possible oxytocic effects of infusions of fresh placenta in normal saline. To our great surprise, it was found that the infusion had a strong oxytocic action on pregnant and nonpregnant adult guinea-pig uteri, and that from 1 g of the sheep placenta, an oxytocic effect equipotent with 2.5 60 IU of oxytocin could be obtained. Pregnant and non-pregnant rat uteri were also stimulated, The oxytocic activity was not affected by boiling or by autoclaving the infusion for 15 min at 121°C at a pressure of 1.05 kg/cm 2. It was therefore decided to examine the oxytocic effects of normal saline extract of the pulverized dried placenta on pregnant and non-pregnant mature guinea-pig uterus, and on pregnant ratuterus. The effects of heat, changes in pH of the extract, and enzyme hydrolysis with trypsin and pepsin on the oxytocic activity were then investigated. The effect of the saline extract on the intestine (guinea-pig ileum) and on the cardiovascular system using four animal models were also examined.
The dried placenta was then pulverized in a ceramic mortar and the powder was stored in a desiccator. Ten g aliquots of the powder were extracted at room temperature with 25 ml of normal saline t~r 3 h, after which it was centrifuged at 4800 rev./min for l0 rain. The supernatant was collected and stored in a refrigerator at 4°C. Any volume of the extract, therefore, was easily related to the weight of the powdered placenta and thus to the weight of the fresh placenta. The weight of the extract was expressed as weight of dry placenta which produced that quantity of extract.