INFLUENCE OF OVARIECTOMY AND PHOTOSTIMULATION ON LEUTEINIZING HORMONEIN THE DOMESTIC TURKEY - EVIDENCE FOR DIFFERENTIAL REGULATION OF GENE-EXPRESSION AND HORMONE-SECRETION

We have investigated the effects of ovariectomy (OVX) and photostimula tion (PS) on anterior pituitary LHbeta mRNA abundance and circulating levels of LH in the domestic turkey. The birds were divided into the f ollowing four treatment groups: non-PS SHAM, PS SHAM, non-PS OVX, and PS OVX. Photostimulation was initiated 7 days after OVX. Anterior pitu itaries and blood samples were collected on Days 0, 1, 3, 7, 14, and 2 6 after PS. The experiment was terminated when the PS SHAM birds were laying eggs regularly. Photostimulation of intact birds induced an inc rease in both LHbeta mRNA levels (Days 3, 14, and 26 of PS) and serum LH (Days 14 and 26 of PS; p < 0.05), while OVX of non-PS birds signifi cantly elevated LH on Days 7, 10, 21, and 33 and LHbeta mRNA levels on Days 7, 8, 10, 14, and 33 post-OVX. Circulating LH titers in the PS O VX birds were well above the levels in the non-PS OVX group (p < 0.005 ); however, LHbeta mRNA abundance was not significantly greater (p > 0 .05). Our results indicate that OVX and PS appear to be additive in st imulating LH secretion but do not have this effect on LHbeta mRNA leve ls. We have hypothesized that gonadectomy induces near-maximal accumul ation of LHbeta mRNA and that therefore the subsequent stimulus of a l ong photoperiod has no additional effect. We suggest that increases in serum LH levels, beyond those of the OVX bird, may be controlled post -transcriptionally.