Influence of ovariectomy and photostimulation on luteinizing hormone in the domestic turkey: Evidence for differential regulation of gene expression and hormone secretion

We have investigated the effects of ovariectomy (OVX) and photostimulation (PS) on anterior pituitary LHβ mRNA abundance and circulating levels of LH in the domestic turkey. The birds were divided into the following four treatment groups: non-PS SHAM, PS SHAM, non-PS OVX, and PS OVX. Photostimulation was initiated 7 days after OVX. Anterior pituitaries and blood samples were collected on Days 0, 1, 3, 7, 14, and 26 after PS. The experiment was terminated when the PS SHAM birds were laying eggs regularly. Photostimulation of intact birds induced an increase in both LHβ 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 significantly elevated LH on Days 7, 10, 21, and 33 and LHβ mRNA levels on Days 7, 8, 10, 14, and 33 post-OVX. Circulating LH titers in the PS OVX birds were well above the levels in the non-PS OVX group (p < 0.005); however, LHβ mRNA abundance was not significantly greater (p > 0.05). Our results indicate that OVX and PS appear to be additive in stimulating LH secretion but do not have this effect on LHβ mRNA levels. We have hypothesized that gonadectomy induces near-maximal accumulation of LHβ mRNA and that therefore the subsequent stimulus of a long photoperiod has no additional effect. We suggest that increases in serum LH levels, beyond those of the OVX bird, may be controlled post-transcriptionally.