We have previously reported that the hyperprolactinemia in incubating turkey hens is associated with recruitment of lactotrophs in the pituitary gland. In this study we have used double immunofluorescence and in situ hybridization histochemistry to 1) identify mammosomatotrophs in the anterior pituitary gland of egg-laying turkey hens and incubating hens, and 2) verify PRL gene expression within mammosomatotrophs by colocalizing PRL messenger RNA in GH-immunoreactive (ir) cells. The pituitaries of laying and incubating turkey hens were collected, and the midsagittal sections were dual labeled for either PRL and GH or PRL messenger RNA and GH. The plasma PRL concentrations were higher in incubating 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 proportion 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%). Furthermore, PRL gene expression was observed in many GH-ir cells in the incubating hen pituitary gland. These data suggest that 1) mammosomatotrophs are present in the turkey pituitary gland, and 2) there is an increased abundance of mammosomatotrophs in the incubating turkey hen that may contribute to hyperprolactinemia.
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