CHANGES OF IMMUNOREACTIVE INHIBIN, FOLLICLE-STIMULATING-HORMONE, LUTEINIZING-HORMONE, AND PROGESTERONE IN PLASMA AFTER SHORT-TERM FOOD-DEPRIVATION AND DURING THE OVULATORY CYCLE OF THE DOMESTIC HEN

The interrelationship between immunoreactive inhibin and follicle-stim ulating hormone (FSH) was measured in laying hens after short-term foo d deprivation and during the ovulatory cycle. Plasma inhibin was estim ated by a heterologous radioimmunoassay validated for use in chicken. FSH was measured by a recently developed homologous radioimmunoassay. Ten hens were deprived of food for 10 days (a method to induce artific ial moult or to stop egg laying). Blood samples were taken daily via t he brachial vein for 10 consecutive days starting on the day of food w ithdrawal. The data are expressed in relation to the last day of ovipo sition. Short-term food deprivation, followed by ovarian atrophy, sign ificantly depressed the plasma inhibin and progesterone (P-4) concentr ation. Plasma FSH concentrations significantly increased, while lutein izing hormone (LB) concentrations slightly but not significantly decre ased. In another experiment, 6 hens were induced to moult. The control hens (n = 6) were fed ad libitum. On Day 17, the hens were killed and follicular distribution was studied. The atrophy of the large yolky f ollicles in restricted hens was associated with a significant increase in the number of white follicles. In a third experiment, serial blood samples were taken from hens (n = 15) at 2-hr intervals for 36 hr via a brachial cannula. Plasma immunoreactive inhibin and FSH concentrati ons did not vary during the ovulatory cycle. LH and P-4 increased simu ltaneously from basal levels to preovulatory peak values 6 hr before o vulation. In conclusion, the inverse relationship between concentratio ns of FSH and inhibin after induced egg laying stop suggest that, as i n mammals, inhibin is important for the inhibition of FSH secretion in the chicken. However, during the ovulatory cycle no such correlation was found. (C) 1994 Academic Press, Inc.