EFFECTS OF GROWTH-HORMONE, PROLACTIN, INSULIN-LIKE GROWTH-FACTORS, AND GONADOTROPINS ON PROGESTERONE SECRETION BY PORCINE LUTEAL CELLS

Growth hormone (GH) and IGF-I have receptors within the corpus luteum (CL) and stimulate CL function. Our objective was to investigate the e ffects of GH, prolactin (PRL), IGF-I, IGF-II, LH, and FSH on progester one secretion by porcine luteal cells during mid-pregnancy. Gilts (cro ssbred Yorkshire/Landrace) were slaughtered on d 44 of pregnancy and C L were collected. Large and small luteal cells (LLC and SLC, respectiv ely) were obtained from dissociated CL and separated by elutriation. L uteal cells were incubated with 0, 1, 10, or 100 ng/mL of GH, PRL, IGF -I, IGF-II, LH, and FSH or combinations of 10 ng/mL of these reagents for 24 or 48 h. Culture media were harvested and concentrations of pro gesterone analyzed by radioimmunoassay. Growth hormone, PRL, and IGF-I increased (P < .05; 100 ng/mL dose) concentrations of progesterone in media of LLC. Insulin-like growth factor-II, LH, and FSH had no effec t on progesterone in LLC cultures. In SLC cultures, GH, PRL, IGF-I, IG F-II, and FSH failed to stimulate progesterone secretion, whereas LH i ncreased progesterone secretion (linear effect of dose; P < .05). Comb inations (10 ng/mL each hormone) of GH and IGF-I or PRL and IGF-I incr eased progesterone secretion by LLC compared with control, GH, PRL, or IGF-I alone (P < .05). Similar combinations of GH or PRL with IGF-I h ad no effect on SLC. Conclusions are that GH and PRL are stimulatory t o progesterone secretion by LLC (location of GH receptor) and SLC are responsive to LH during midpregnancy. Both GH and PRL are synergistic with IGF-I for increased progesterone secretion.