Endocrine Abstracts

Secretion of LH and FSH from the anterior pituitary are regulated by hypothalamic GnRH and TGF beta-superfamily members, inhibin and activin. The aim of this study was to identify expression of key receptors in the pituitary gland and monitor their expression throughout the 24-25h ovulatory cycle.

Hens maintained on long days (16L:8D) were killed by cervical dislocation 4h, 12h, 18h and 22h after predicted ovulation of a midsequence egg (n=8 per group). Pituitary glands were dissected, RNA extracted and cDNA synthesized. Plasma concentrations of LH, FSH, progesterone and inhibin A were measured.

The mRNAs encoding betaglycan, gonadotrophins, GnRH receptors (GnRH-R) and activin receptor (ActR) subtypes (type I, IIA, IIB) were quantified and expressed relative to total cDNA. Significant changes in expression (P<0.05) of ActRIIA and betaglycan mRNA were found, peaking 18h after ovulation, just prior to the preovulatory LH surge (20.67 and 1.02 amol/microgram cDNA respectively) and minimal 22h postovulation, after the LH surge (9.30 and 0.67 amol/microgram cDNA respectively). Expression of GnRH-R was highest 18h after ovulation (29.75 amol/microgram cDNA) and lowest 4h after ovulation (8.53 amol/microgram cDNA).

No significant changes were observed in the expression of the mRNAs encoding LH-beta subunit (range- 0.65 to 0.92 fmol/microgram cDNA), FSH-beta subunit (range- 0.04 to 0.10 fmol/microgram cDNA) and ActRI (range- 14.44 to 24.32 amol/microgram cDNA) throughout the ovulatory cycle, although both LH and FSH-beta subunit mRNA expression levels were lowest 22h after ovulation.

These results are consistent with an endocrine and/or local role of inhibin/activin signalling in the modulation of gonadotroph function during the ovulatory cycle.