Postnatal uterine development in Inverdale ewe lambs.

Postnatal development of the uterus involves, particularly, development of uterine glands. Studies with ovariectomized ewe lambs demonstrated a role for ovaries in uterine growth and endometrial gland development between postnatal days (PNDs) 14 and 56. The uterotrophic ovarian factor(s) is presumably derived from the large numbers of growing follicles in the neonatal ovary present after PND 14. The Inverdale gene mutation (FecXI) results in an increased ovulation rate in heterozygous ewes; however, homozygous ewes (II) are infertile and have ‘streak’ ovaries that lack normal developing of preantral and antral follicles. Uteri were obtained on PND 56 to determine whether postnataluterine developmentdiffersbetween wild-type (CC) and II Inverdale ewes. When comparedwithwild-type ewes, uterineweight of II ewes was 52% lower, and uterine horn length tended to be shorter, resulting in a 68% reduction in uterine weight:length ratio in II ewes. Histomorphometrical analyses determined that endometria and myometria of II ewes were thinner and intercaruncular endometrium contained 38% fewer endometrial glands. Concentrations of estradiol in the neonatal ewes were low and not different between CC and II ewes, but II ewes had lower concentrations of testosterone and inhibin-a between PNDs 14 and 56. Receptors for androgen and activin were detected in the neonataluteri ofbothCCand IIewes. These results support the concept thatdeveloping preantraland/orantral folliclesof the ovary secrete uterotrophic factors, perhaps testosterone or inhibin-a, that acts in an endocrine manner to stimulate uterine growth and endometrial gland development in the neonatal ewes. Reproduction (2008) 135 357–365