Submitted to: Life Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 1995
Publication Date: N/A
Interpretive Summary: Heat stress is a significant cause of production losses in baby pigs. Prolactin (PRL) and growth hormone (GH) are hormones which respond to heat exposure in mature pigs. It is important to know whether these hormone responses occur in neonatal pigs. Hormone-producing cells of the anterior pituitary glands of piglets reared for 5 weeks in a hot or cool environment twere evaluated for their ability to produce and release PRL and GH. Pituitary cells from piglets exposed to the hot environment contained and released more PRL than cells from piglets reared under cool conditions. No differences in GH-producing cell function existed between thermal groups. Prolactin may be a hormone which can be used as a biochemical indicator of potentially stressful conditions in neonatal pigs. This information could be applied to identifying and understanding conditions needed for optimal animal well-being. Benefits may be realized in the areas of animal production and animal ethology.
Technical Abstract: The present study evaluated the effect of a constant hot (32 deg C) or cool (21 deg C) thermal environment (TE) on lactotroph and somatotroph secretory activity in 33-day-old barrows and gilts. 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, and 100 0nM thyrotropin-releasing hormone (TRH); and .1, 1, and 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); and 59 mM KCl. Prolactin secretion in culture was stimulated by TRH and by pharmacological treatments (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 stimulation (p < .0001). 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.