UNEVEN REGIONAL DISTRIBUTIONS OF PROLACTIN-SECRETING AND GROWTH HORMONE-SECRETING CELLS AND SEXUALLY DIMORPHIC PROPORTIONS OF PROLACTIN SECRETORS IN THE ADENOHYPOPHYSIS OF ADULT CHICKENS

Prolactin (PRL) and growth hormone (GH) proteins ale structurally simi lar and are thought to be evolutionarily derived from a common gene. I n addition, data indicate that GH and PRL cells differentiate from a c ommon stem cell. In adult birds, females have higher levels of serum P RL than males. Levels of serum GH are reported to be higher in young m ale birds than in females and equal between sexes in adult birds. Furt hermore, previous studies using immunocytochemistry found that PRL- an d GH-containing cells were located primarily in the cephalic (Cp) and caudal (Cd) lobes, respectively, of the anterior pituitary. Two experi ments were conducted to study the cellular basis for differences in PR L and GH secretion between genders or anatomical location in adult chi ckens. In Experiment I, anterior pituitaries from broiler breeder adul t hens and roosters were subjected to reverse hemolytic plaque assays (RHPA's) for PRL and GH. The percentage of PRL-secreting cells was sig nificantly greater in females than in males (46.1+/-4.5% and 26.1+/-2. 4%, respectively; P < 0.001; n = 6). However, there were no significan t differences between the proportions of GH-secreting cells between se xes (25.8+/-3.1% and 30.0+/-3.9% in females and males, respectively). Average area of plaques formed was different between sexes in GH plaqu e assays under basal conditions (162,465.9+/-29,911.8 mu m(2) and 53.8 34.9+/-31,033.5 mu m(2), for males and females, respectively; P < 0.05 ). However, no differences were found in the presence of GH-releasing hormone. In Experiment Il, anterior pituitaries from Leghorn hens were dissected into three regions: the extreme portions of the Cp and Cd l obes and the remaining or middle portion. The cells from each region w ere subjected to RHPA's for PRL and GH. We found that 52.0+/-4.1% of a ll cells from the Cp lobe secreted PRL. This proportion was greater (P < 0.01; n = 4) than that found in the Cd lobe, where 2.4+/-0.4% of al l cells released PRL. In contrast, the percentage of GH-secreting cell s was higher in the Cd lobe than in the Cp lobe (61.0+/-2.3% and 0.8+/ -0.5%, respectively; P < 0.01). As expected, the middle portion contai ned substantial numbers of both cell types. These findings suggest tha t sexual dimorphism in serum PRL levels in adult chickens is due, in p art, to an increased cell population of PRL secretors in females. Furt hermore, PRL- and GH-secreting cells are distributed unevenly througho ut the anterior pituitary of chickens, with the PRL secretors localize d to the Cp lobe and the GH secretors to the Cd lobe. (C) 1995 Academi c Press, Inc.