Somatotroph, lactotroph and thyrotroph function in three-week-old gilts reared in a hot or cool environment

The influence of the thermal environment on the ability of the pituitary gland to secrete growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) was examined in gilts reared under hot (H: 27-32 degrees C, 50-90% RH, n = 6) or cool (C: 20 degrees C, 50% RH, n = 6) conditions. Piglets were sacrificed at 3 wks of age. Pituitary cells from each animal were cultured and exposed to vehicle (culture medium); 1, 1, and 10 nM thyrotropin-releasing hormone (TRH); .1, 1, and 10 nM growth hormone-releasing hormone (GHRH); 59 mM KCl; 2 mM 8-Br-cAMP; and 100 nM phorbol myristate acetate. Rearing in the H, compared to the C, environment increased plasma PRL concentrations (p < .001), in vitro PRL secretion subsequent to all secretagogue treatments (p < .001), and cellular PRL content (p < .001). The stimulated release of TSH in culture was reduced (p < .001), but cellular TSH content was increased (p < .05) by exposure to the H environment. The total amount of TSH in culture (secreted + cellular) was not affected by thermal environment. The release of GH in vitro, cellular GH content, total GH in culture, and plasma GH concentrations were similar between H and C groups. The only dose-response curves that differed in slope between thermal groups were those produced by the TSH response to TRH (p < .001). The results of this study suggest that chronic exposure to a hot environment can 1) enhance PRL secretion by a mechanism which affects the quantity of releasable PRL rather than lactotroph sensitivity to secretagogues and 2) reduce TSH secretion by inhibiting thyrotroph secretory response to stimulation.