Development of the infantile mouse uterus: the effect of stilboestrol.

Arecent study (Dullaart, Kent & Ryle, 1975) showed high serum gonadotrophin levels in infantile mice. Initially, the concentration ofLH and FSH rose steadily, the former reaching a peak concentration around 9 days after birth then falling by 13 days to the range found in pubertal serum. The concentration of FSH, however, continued to rise until 13 days. The rise in endogenous gonadotrophin levels between 4 and 9 days coincides with rising activities of gonadotrophin\x=req-\ responsive ovarian NAD and NADP diaphorases (Kent & Ryle, 1975). Marked 3\g=b\-hydroxysteroiddehydrogenase activity is also present in mouse ovaries at this age (Hadjioloff, Bourneva & Motta, 1973). Increasing steroid biosynthesis, perhaps of oestrogens, may therefore occur and lead to the suppression of LH release. To investigate this possibility, uterine development was studied during the infantile period. In addition, very young mice were treated with stilboestrol to see whether the uterine changes seen during normal development could be induced prematurely. Mice of the CFW outbred strain were reared in foster litters of ten females as in the study of ovarian morphology and serum gonadotrophin levels (Kent, 1972; Dullaart et al., 1975). To investigate normal development, pairs of mice from a single litter were killed on Days 4, 5, 6 and 7 and pairs from a second litter were killed on Days 7, 8, 9, 10 and 11. As each pair was removed, it was replaced with males of the same age to maintain a constant litter size. The uteri