Contribution of endogenous inhibin to the decline of the secondary surge of follicle-stimulating hormone in the XXXX .

@entity35 @entity19610
The involvement of inhibin in the decline of the secondary surge of follicle-stimulating hormone (FSH) was investigated in the @entity35 . After ovariectomy or treatment with inhibin antiserum conducted at 2300 hours during pro-oestrus, plasma concentrations of FSH were maintained at high levels compared with control @entity35 . However, plasma FSH started to decline at 0500 hours during oestrus in both the groups. The same treatments conducted during metoestrus markedly increased plasma FSH after 24 h (twofold compared with the treatments during pro-oestrus), suggesting that the treatments sufficiently depleted circulating inhibin. To examine whether the decline of plasma FSH occurred through a transcriptional mechanism or through a translational mechanism, @entity19610 mRNA expression and the pituitary concentration of FSH were measured. Neither ovariectomy nor inhibin immunization conducted during the night of pro-oestrus, affected the pituitary concentration of FSH after 24 h, whereas a noticeable increase was observed after the treatments conducted during metoestrus. In both stages, both ovariectomy and inhibin immunization significantly increased @entity19610 mRNA expression compared with control @entity35 . In contrast with the pituitary concentration of FSH, the effect of inhibin immunization on @entity19610 mRNA expression was not different between the stages. The present data demonstrate the involvement of inhibin in the decline of the secondary surge of FSH, and suggest that a factor or factors other than inhibin may also be responsible for the fall in FSH. Changes in the pituitary concentration of FSH and @entity19610 mRNA expression suggest that post-transcriptional mechanisms may be involved in the suppression of FSH secretion during oestrus.
