OVARIAN INVOLVEMENT IN THE SUPPRESSION OF LUTEINIZING-HORMONE IN THE INCUBATING TURKEY (MELEAGRIS-GALLOPAVO)

A series of experiments were conducted to elucidate the role of the ovary in incubation behavior-associated luteinizing hormone (LH) suppression. Ovariectomy (Ovx) increased (p < 0.05) serum LH levels in nonphotostimulated, laying and photorefractory turkeys but not in incubating birds (p > 0.05). Ovx had no effect on intramuscularly injected mammalian luteinizing hormone-releasing hormone (4 mug/kg i.m.)-induced LH in incubating hens, but enhanced the LH response in laying hens. Serum LH and prolactin (Prl) were unaffected by Ovx, and nest deprivation (ND) decreased Prl levels (p < 0.05) with no effect on serum LH of incubating turkeys. However, serum LH increased (p < 0.05) and Prl decreased in Ovx-ND birds. Prl mRNA abundance (11.9 +/- 1.2 ng/mug total RNA) decreased following Ovx (3.4 +/- 0.4 ng/mug total RNA) or ND (3.6 +/- 0.5 ng/mug total RNA). Nest deprivation increased LHbeta mRNA (2.5-fold) which was further increased (4.8-fold) by Ovx. Hypothalamic GnRH-1 and GnRH-11 contents increased (p < 0.05) in Ovx-ND turkeys. We conclude that serum LH suppression during incubation behavior requires ovarian participation acting synergistically with elevated Prl and/or nesting stimulus on hypothalamic GnRH, and that the concentration fo LHbeta mRNA may be a limiting factor in LH secretion.