Changes in pituitary somatotroph and lactotroph distribution in laying and incubating turkey hens

Turkey hens can rapidly shift from a laying condition to one characterized by ovarian regression, incubation behavior, and hyperprolactinemia. Although remarkable changes occur in hormonal profiles as turkey hens pass from a laying to an incubating state, studies have not been undertaken to examine histochemical alterations of functionally relevant pituicytes in the adenohypophysis. The objective of this study was to compare the immunocytochemical changes in pituitary lactotrophs and somatotrophs in incubating turkey hens with those of egg laying hens. Based upon nest visiting and egg production records, laying and incubating hens were selected for sampling blood, pituitaries, and ovaries. Plasma prolactin (PRL) and growth hormone (GH) concentrations were determined. Sagittal pituitary sections of laying and incubating hens were immunostained using antibodies against turkey growth hormone or synthetic chicken PRL peptide. Somatotrophs were found predominantly in the caudal lobe while lactotrophs occurred only in the cephalic lobe of adenohypophysis in laying hens. In incubating hens, somatotrophs in the ventral half of the caudal lobe were replaced by lactotrophs. The sagittal area which immunostained for PRL was significantly greater while the area that immunostained for GH was less in the adenohypophysis of incubating turkey hens. Some of the lactotrophs were hypertrophied in incubating hens. The lactotrophic recruitment and hypertrophy provide a cellular basis for the hyperprolactinemia in incubating turkey hens.