Influence of season and sex on the inhibitory effect of ovine follicular fluid on plasma gonadotrophins in gonadectomized sheep.

The inhibitory effects of follicular fluid on FSH secretion were similar in gonadectomized male and female sheep, and in the anoestrous and breeding seasons. Significant suppression of LH was variable and was observed only at the highest dose of follicular fluid when suppression rarely exceeded 50% of pretreatment values. Basal plasma FSH and LH concentrations were higher in castrated males than in ovariectomized females in both seasons. Plasma FSH concentrations in gonadectomized males and females and LH concentrations in the males were lower in the anoestrous than the breeding season. Therefore, in the absence of the gonads, sex and photoperiod can influence hypothalamic control of basal pituitary gonadotrophin secretion in males and females, whereas the feedback effect of non-steroidal factors in follicular fluid (inhibin) on FSH secretion is not influenced by photoperiod or sex.