GnRH-dependent and -independent components of FSH secretion after acute treatment of anoestrous ewes with ovine follicular fluid and a GnRH antagonist

摘要

Gonadotrophin and inhibin concentrations were measured in anoestrous ewes after acute treatment with either saline, ovine follicular fluid (oFF), GnRH antagonist, or oFF and GnRH antagonist in combination. The increase in mean LH concentrations observed in ewes treated with oFF alone, was not seen in either of the groups treated with GnRH antagonist, in which LH pulsatility was completely inhibited. This result suggests that the LH rebound that follows follicular fluid treatment is GnRH dependent. Blockade of GnRH had no effect on the suppression of FSH seen after follicular fluid injection, indicating that this component of FSH secretion is independent of short-term GnRH input. After this initial suppression, a rebound release of FSH was seen in the group treated with oFF alone. The addition of GnRH antagonist appeared to decrease the rebound, suggesting that this rebound release of FSH may have a GnRH-dependent component. Inhibin concentrations in both oFF-treated groups increased after oFF injection and then declined to pretreatment values. However, a second rise in inhibin concentration, concomitant with the FSH rebound in ewes receiving oFF alone, was seen in the group treated with oFF and GnRH antagonist. As this rise in endogenous inhibin concentration could also act to suppress the rebound release of FSH, it cannot be conclusively proved from this study that GnRH input is required for the generation of the rebound release of FSH after treatment with oFF.