The diameters of the ovarian, uterine, and femoral veins and the inferior vena cava were measured during stages of the estrous cycle in intact and hysterectomized mice and at intervals during pregnancy in mice with embryos in both uterine horns or in only the left horn. At metestrus I vein sizes were the least and were not significantly different in intact and hysterectomized mice. Ovarian and uterine veins showed the same or increased diameters at other stages of the cycle; veins enlarged progressively during pregnancy in intact mice. Non-gravid uterine horns showed little size increase as compared to gravid horns. Increases in vein diameter appeared to be correlated with local production of reproductive hormones. Evidence for transuterine migration of embryos was observed in 21 of 53 mice in which one uterine tube had been ligated or one ovary had been removed.

Ligation of pellets of various steroid hormones to the uterine horns of ovariectomized adult mice may be followed by a significant increase in venous diameter (1, 2 ) . The present research concerns the effect on vein size of steroid pellets in adult orchidectomized, ovariectomized, and ovariectomized-hysterectomized mice.Materials and Methods. Cylindrical, uniformly compressed, 3.5-4.5 mg pellets of single crystallline steroids without excipient were prepared (3). The steroids were progesterone, estrone, estradiol-l7,8, testosterone, and dihydrotestosterone (%-androstan-l7,8-ol-3-one). Glass pellets of the same size and shape were also made. All mice were Jackson Laboratory B6D2F1 (C57BL/ 6-Jo X DBA/2-J 8 ) adults.

Pellets of progesterone plus 1% 16alpha-hydroxy-progesterone (16alpha-OH), testosterone plus 1% 16alpha-OH, and estradiol-17beta plus 1% 16alpha-OH were implanted in the right uterine fat mass in ovariectomized (O) and ovariectomized-hysterectomized (OH) mice. Three weeks later they were killed and the diameters of the ovarian, uterine, and femoral veins and the inferior vena cava were measured and averaged. The averages were compared with averages for O and OH mice bearing pellets of glass and of progesterone, testosterone, and estradiol-17beta without 16alpha-OH. It is concluded that in castrate mice the size of ovarian and uterine veins is influenced not by the presence or absence of the uterus but by sex steroids, that progesterone usually causes decreases while testosterone and estradiol-17beta cause increases in vein diameter, and that both the presence of the uterus and the administration of 1% 16alpha-OH are associated with partial inhibition of increases in vein size induced by steroids. Uterine hypertrophy and urinary bladder distention resulting from the administration of testosterone and estradiol-17beta were not prevented by the addition of 1% 16alpha-OH.