THE ENDOCRINE CONTROL OF THE EXTRA-UTERINE WEIGHT GAIN OF PREGNANT MICE

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Abstract
SUMMARY: The extra-uterine weight gain of pregnancy in mice was maintained after removal of the ovaries and placentae (by hysterectomy) by giving progesterone alone in apparently physiological concentrations. Cessation of treatment was followed by a fall in weight, as after parturition or pseudo-parturition; the degree of protection against the weight loss and the subsequent loss occurring after treatment were each proportional to the quantity of the hormone given. Stimulation of luteal activity by gonadotrophin after hysterectomy without spaying in pregnancy similarly prevented the loss of weight. Progesterone implants in non-pregnant mice caused a steady weight gain of a similar order to the extra-uterine weight increase of pregnancy, accompanied by anoestrus; removal of the tablets precipitated a rapid return of weight to initial levels and a return to oestrus. These and subsidiary findings support a hypothesis that the weight increase during pregnancy in the mouse is under the control of ovarian progesterone, the luteal activity being maintained by the presence of placentae in the uterus (probably by placental luteotrophin). Oestrogens, in the quantities given, were incapable of maintaining the weight after hysterectomy in pregnancy, with or without removal of the ovaries, and had no potentiating effect upon suboptimal quantities of progesterone. Oestrogens, therefore, appear neither to play any part in the weight gain of pregnancy nor to exhibit luteotrophic activity. Hysterectomy in the mouse was not observed to prolong the life of the corpora lutea of pregnancy.