Lactotroph and somatotroph function in piglets reared in a constant hot environment

The present study evaluated the effect of rearing in a constant hot (32 degrees C) or cool (21 degrees C) thermal environment (TE) on lactotroph and somatotroph secretory activity in 5-wk-old barrows (castrate males) and gilts (female). Pituitary cells from seven gilts and seven barrows from each TE were cultured at a density of 250,000 cells/1 ml well and exposed to vehicle (culture medium); .1, 1, 10, or 100 nM thyrotropin-releasing hormone (TRH); or .1, 1, or 10 nM growth hormone-releasing hormone (GHRH). Post-receptor cellular stimulation was induced pharmacologically with 2 mM 8-Br-cAMP (cAMP); 100 nM phorbol myristate acetate (PMA); or 59 mM KCl. Prolactin secretion in culture was stimulated by TRH and by pharmacological compounds (p < .0001). In vitro PRL secretion was increased approximately two-fold in the hot environment (p < .02). Similarly, cellular PRL content in the hot TE was twice that in the cool TE (p < .01). The in vitro secretion of growth hormone (GH) was increased by GHRH and by pharmacological compounds (p < .0001), but was unaffected by TE (p > .5). No effects of sex (p > .3) or sex x TE interactions (p > .2) were detected in any endpoint. The results of this study demonstrate that lactotroph, but not somatotroph, secretory activity is enhanced by a constant hot TE in early postweaning pigs. This increase in secretory activity does not appear to be dependent on receptor-mediated cellular activation, but may reflect enhanced levels of cellular PRL available for release.