Increase in Ovarian α-Inhibin Gene Expression and Plasma Immunoreactive Inhibin Level Is Correlated with a Decrease in Ovulation Rate in the Domestic Hen

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This study was designed to examine the relationship among ovulation rate, inhibin α-subunit gene expression, and plasma immunoreactive inhibin levels between hens laying at a high ovulation rate and hens laying at a low ovulation rate. A porcine inhibin α-subunit cDNA was used to examine the expression of inhibin α-subunit in the granulosa cell layers of preovulatory chicken follicles. Total RNA was extracted from granulosa layers of hens laying at a high and low rate and used in slot blot analyses. A dose-related increase in signal intensity with increasing doses of RNA for hens laying at a high and low rate was observed. The expression of the α-subunit of inhibin (per microgram of RNA) in granulosa layers of hens laying at a low rate was found to be greater than that in hens laying at a high rate ( P < 0.001). Different groups of hens laying at the same rates as those used in the RNA determinations were selected for determination of plasma inhibin levels. Plasma samples from those hens laying at a high and low rate were collected from 1000 to 1800 hr at 2-hr intervals. Plasma inhibin, luteinizing hormone (LH), and follicle stimulating hormone (FSH) were determined by RIA. Plasma inhibin level was higher in hens laying at a low rate than that in those laying at a high rate ( P < 0.05), while plasma LH level in hens laying at a low rate was lower than that in hens with a high ovulation rate ( P < 0.01). There was no difference in plasma FSH level associated with rate of lay. Results in this study suggest that the ovulation rate-related changes in inhibin α-subunit gene expression and plasma immunoreactive inhibin level do not directly affect ovulation rate through a modulation of plasma FSH level.