GONADOTROPH FUNCTION IN 3-WEEK-OLD GILTS REARED IN A WARM OR COOL THERMAL ENVIRONMENT

The present study evaluated the effect of a warm (cycling 27-32 degree s C, 50-70% RH) or cool (21 degrees C, 55% RH) thermal environment (TE ) on gonadotroph function in 3-week-old gilts (females). Pituitary cel ls from twelve gilts reared in each TE were cultured at a density of 2 50,000 cells/1 ml well and exposed to vehicle (culture medium); .l, 1, and 10 nM gonadotropin-releasing hormone (GnRH); 2 mM 8-Br-cAMP (cAMP ); and 100 nM phorbol myristate acetate (PMA). Luteinizing hormone (LH ) and follicle-stimulating hormone (FSH) secretion in culture were sti mulated by GnRH and by pharmacological compounds (p < .0001). In vitro LH secretion was approximately three-fold higher in the warm, compare d to the cool, TE group (p < .0001). Similarly, cellular LH content in the warm TE exceeded that in the cool TE (p < .005). The in vitro sec retion of FSH and cellular FSH content were significantly elevated in the warm TE (p < .02). Serum LH concentrations in the warm and cool TE were 7.01 +/- 1.75 and 2.13 +/- .44 ng/ml, respectively (p < .02). Se rum FSH concentrations were 6.38 +/- .53 and 4.59 +/- .28 ng/ml in the warm and cool TE, respectively (p < .01). The results of this study d emonstrate that secretory responses of gonadotrophs in early postweani ng pigs are influenced by chronic TE exposure. These differences in se cretory activity may reflect levels of cellular gonadotropin available for release.