THE PHYSIOLOGY OF PREGNANCY IN THE RAT. FURTHER DATA BEARING ON THE PROLONGATION OF PREGNANCY WITH A STUDY OF THE EFFECTS OF OÖPHORECTOMY DURING PREGNANCY

Abstract

1. Previous work showed that the gestation period in the rat could be prolonged by the injection of substances rich in gonadotropic hormones, but containing no growth hormone [Hain, 1932 b]. The results in this paper show that it can be prolonged by an extract of anterior pituitary rich in growth hormone (phyone), and having only a slight ovarian reaction.2. The ovarian reaction was the same with both extracts and was of a typical character, namely, the production of hawmorrhagic follicles or “blood points.” It is considered unlikely that the substance producing this effect was, by itself, responsible for the prolongation of pregnancy. The most probable alternative is the existence of a hitherto unknown hypophyseal factor which causes the prolongation of pregnancy. Channels through which it may act are briefly examined.3. The combination of oophorectomy with injections of the abovementioned extracts shows that the presence of the ovaries is essential for the production of the full effects of the extracts in the prolongation of pregnancy.4. Oöphorectomy interrupts pregnancy, but the action is nlot immediate, and removal of the corpus luteum does not cause evacuation of the uterus. Considerable fcetal and placental development takes place in the absence of the ovaries, but the ovaries are necessary for full‐term development in the rat.Parturition can occur in the absence of the ovaries, but in such event it is protracted. This feature was common also to the group in which anterior pituitary extract was injected, and it is suggested that in both cases parturition may have occurred without ovarian action. Since parturition is protracted after removal of the ovaries and is completely prevented in absence of the anterior pituitary, it seems probable that ovarian‐hypophyseal action is essential to the rapid expulsion of the fœtus and to ensure live births; at the same time the existence of another factor in the birth mechanism is strongly indicated.