THE PHYSIOLOGY OF PREGNANCY IN THE RAT: AN HORMONAL INVESTIGATION INTO THE MECHANISM OF PARTURITION. EFFECT ON THE FEMALE RAT OF THE ANTE-NATAL ADMINISTRATION OF STRIN TO THE MOTHER

¹ Institute of Animal Genetics, University of Edinburgh

1. "Delayed" abortion (i.e. 36-72 hours after the last injection) following multiple injections of iestrin was less frequent in rats than in mice; very large amounts of cestrin were required; there was no "immediate" abortion (i.e. within 1-6 hours of the last injection). The gestation period was sometimes prolonged by 3-5 days after the injection of large quantities of oestrin.

2. The subsequent injection of an extract of anterior pituitary or of an oestrin-free extract of human pregnancy urine did not cause a significant increase in the percentage of "delayed" abortions which occurred when oestrin alone was injected There was an increase in the number of prolonged pregnancies.

3. The synergism between strin and oxytocin demonstrated in the mouse does not, apparently, exist in the rat.

4. The administration to pregnant rats of placentæ, hypophyses, uterus, and blood of parturient rats did not cause abortion.

5. The process of parturition in the normal pregnant rat is described.

6. A modification of the corpus urethrae involving a displacement of the urethra occurred in all surviving female foetuses born to rats injected with large quantities of cestrin late in pregnancy. The subsequent injection of oxytocin failed to cause abortion in animals in which this modification of the fcetal genitalia was induced.