IMPORTANCE OF THE FEMALE REPRODUCTIVE TRACT IN THE FORMATION OF RELAXIN1

Abstract

Progesterone did not produce relaxation in castrated, hysterectomized guinea pigs while the absence of the ovaries and uterus had no effect on the response to relaxin. This suggests that relaxin is absent in hysterectomized animals given progesterone. Progesterone also brought about the presence of relaxin in the blood of [female] rabbits. The amt. of relaxin in the blood was not correlated with the size of the dose of progesterone nor necessarily with the length of treatment as 0.5 mg. daily for 5 days was nearly as effective as 5 mg. daily for 9 days. Relaxin did not appear in the blood of castrated [male] and castrated, hysterectomized [female] rabbits given similar treatment. This indicates that the [female] reproductive tract is essential for the formation of relaxin in response to progesterone. Estradiol stimulated the formation of relaxin in castrated [female] rabbits but not in castrated, hysterectomized [female][female] nor castrated [male][male]. Also, the effects of estrogens on the pelvic ligaments of castrate [female] guinea pigs greatly facilitated the action of relaxin. Estrogens are known to produce morphological changes in the pelvis of guinea pigs involving resorption of cartilage and bone. Therefore, pelvic relaxation, when induced by estrogens, may be due partly to these structural modifications in addition to the action of relaxin.