IDENTIFICATION OF MAMMOSOMATOTROPHS IN THE TURKEY HEN PITUITARY - INCREASED ABUNDANCE DURING HYPERPROLACTINEMIA

We have previously reported that the hyperprolactinemia in incubating turkey hens is associated with recruitment of lactotrophs in the pitui tary gland. In this study we have used double immunofluorescence and i n situ hybridization histochemistry to 1) identify mammosomatotrophs i n the anterior pituitary gland of egg-laying turkey hens and incubatin g hens, and 2) verify PRL gene expression within mammosomatotrophs by colocalizing PRL messenger RNA in GH-immunoreactive (ir) cells. The pi tuitaries of laying and incubating turkey hens were collected, and the midsagittal sections were dual labeled for either PRL and GH or PRL m essenger RNA and GH. The plasma PRL concentrations were higher in incu bating hens (231 +/- 10.6 ng/ml) than in laying hens (43 +/- 7.4 ng/ml ; P < 0.01). In the midsagittal pituitary sections, mammosomatotrophs were predominantly found scattered in the caudal lobe of the anterior pituitary gland, in the ventral half of the cephalic lobe, and at the junction of cephalic and caudal lobes. In incubating hens, the proport ion of mammosomatotrophs was 7.4 +/- 1.52% (mean +/- SEM) of the total number of GH-ir and/or PRL-ir cells counted, which was significantly higher (P < 0.05) than that found in laying hens (0.6 +/- 0.23%). Furt hermore, PRL gene expression was observed in many GH-ir cells in the i ncubating hen pituitary gland. These data suggest that 1) mammosomatot rophs are present in the turkey pituitary gland, and 2) there is an in creased abundance of mammosomatotrophs in the incubating turkey hen th at may contribute to hyperprolactinemia.