HORMONAL FACTORS INVOLVED IN PARTURITION IN THE RAT

¹ The Research Laboratories, University of Denver

Certain theories which have been suggested to explain the onset of parturition on a hormonal basis were tested by the injection of various hormones and hormone combinations. It was thought that if the average length of the gestation period could be shortened significantly as compared with a large group of controls, this would be evidence that the hormone producing such results was involved in normal parturition. 361 rats, exclusive of controls, were used. The theories tested, and the results obtained, follow.

1. Theory.—Parturition occurs as the result of an increased concentration of estrin late in pregnancy. Results.—Large doses of estrin terminate pregnancy by killing the fetuses. Doses which do not have this effect do not significantly affect the gestation period.

2. Theory.—Parturition occurs as the result of the sensitization of the uterus to pitocin by estrin. Results.—No evidence supporting this theory was discovered.

3. Theory.—The anterior lobe of the pituitary is involved, either directly or by stimulating estrin secretion in the follicles. Results.—Large doses of anterior lobe extract delay parturition. The fetuses die eventually and are either aborted or resorbed. Smaller doses, either with or without pitocin, have no effect.

4. Theory.—Some substance in follicular fluid, placentæ, or blood is responsible. Results.—No such substance could be demonstrated.