CHANGES IN PITUITARY SOMATOTROPH AND LACTOTROPH DISTRIBUTION IN LAYING AND INCUBATING TURKEY HENS

Authors: RAMESH, R - UNIVERSITY OF MARYLAND; Proudman, John; KUENZEL, W - UNIVERSITY OF MARYLAND

Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Prolactin (PRL) and growth hormone (GH) are closely related hormones that are produced by distinct cells in the pituitary gland. Prolactin, which causes incubation behavior and ovarian regression in turkey hens and decreases hatching-egg production, is produced by lactotrophs; GH, which stimulates growth, is produced by somatotrophs. In this report we show that in the laying turkey hen, lactotrophs are found primarily in the cephalic lobe of the anterior pituitary, while somatotrophs are found primarily in the caudal lobe. In the incubating hen, the area of the pituitary populated by lactotrophs increases to include both lobes, while that occupied by somatotrophs declines markedly to include only a small area of the caudal lobe. In addition, lactotrophs of incubating hens were observed to be 50% larger in diameter than those of laying hens. These results demonstrate that the increase in prolactin secretion which results in incubation behavior is due, at least in part, to an increase in the portion of the pituitary which contains lactotrophs, and to an increase in the size of lactotrophs. An increase in lactotroph size likely indicates an increase in prolactin production by the cell, while an increase in lactotroph cell number (at the expense of somatotrophs) suggests that pituitary cell function changes dramatically with the change in reproductive state. This research demonstrates the reproductive failure due to incubation behavior may be due to a change in pituitary cell function.

Technical Abstract: 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 to functionally relevant pituicytes in the adenohypophysis. The objective of the 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 in incubating hens were selected for sampling blood, pituitaries and ovaries. Plasma prolactin and growth hormone concentrations were determined. Sagittal pituitary sections of laying and incubating hens were immunostained using antibodies against turkey growth hormone or synthetic chicken prolactin peptide. Somatotrophs swere found predominantly in the caudal lobe while lactotrophs occurred onl in the cephalic lobe of the adenohypophysis in the laying hen. In incubating hens, somatotrophs in the ventral half of the caudal lobe were replaced by lactotrophs. The sagittal area which immunostained for prolactin was significantly greater while the area that immunostained for growth hormone was less in the adenohypophysis of incubating turkey hens. Some of the lactotrophs were hypertrophied in incubating hens. The lactotrophic proliferation and hypertrophy provide a cellular basis for the hyperprolactinemia in incubating turkey hens.