This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Foster, D. L. Articles by Ryan, K. D. Search for Related Content PubMed Articles by Foster, D. L. Articles by Ryan, K. D.

Premature seasonal inhibition of tonic LH secretion by oestradiol in the female lamb and its consequences

Summary. Patterns of circulating LH were examined in ovariectomized lambs and adults bearing Silastic capsules containing oestradiol-17β and in untreated ovariectomized lambs. A decrease in serum LH in oestradiol-treated lambs occurred coincidentally with the cessation of ovulations in intact lambs and in the absence of any decrease in circulating LH in untreated ovariectomized lambs. On average, these phenomena occurred 3 weeks before the seasonal reduction in serum LH levels and onset of anoestrus in oestradiol-treated ovariectomized and intact adults, respectively. The results suggest that (1) an early seasonal increase in responsiveness to oestradiol negative feedback on tonic LH secretion is responsible for the premature cessation of ovulations in the lamb, accounting, in part, for the short breeding season during the first year of life and, in some lambs, the failure to initiate cyclicity until the second year after birth; and (2) onset of anoestrus in lambs, in contrast to puberty, is not associated with steroid-independent changes in LH secretion.