REGULATION OF REPRODUCTIVE SEASONALITY IN THE RED DEER HIND - ESTRADIOL-DEPENDENT AND ESTRADIOL-INDEPENDENT INFLUENCES ON THE PATTERNS OF LH CONCENTRATIONS

The control of reproductive seasonality was studied in farmed adult re d deer hinds that had been either ovariectomized or ovariectomized and oestradiol-treated (s.c. implants). The breeding season, delineated b y progesterone secretion in intact hind herdmates, was characterized b y high (mean 0.6, range 0.1-2.5 ng ml(-1) plasma) LH concentrations in ovariectomized oestradiol-treated hinds. In contrast, during the non- breeding season plasma LH concentrations in these animals were signifi cantly lower (mean 0.1, range 0-0.9 ng ml(-1) plasma). LH secretion in ovariectomized untreated hinds also displayed a marked seasonal patte rn, approximately the inverse of daily photoperiod (that is, a winter peak and summer trough). The pituitary LH response to 10 mu g exogenou s GnRH was also maximal during the breeding season in ovariectomized ( mean 7.4, range 1.2-14.6 ng ml(-1)) and ovariectomized, oestradiol-tre ated (mean 16.4, range 1.4-32.3 ng ml(-1)) hinds. These results indica te that LH secretion in the hind is regulated by both steroid-dependen t and -independent mechanisms.