EFFECTS OF LH, PROSTAGLANDIN E-2, 8-BROMO-CYCLIC AMP AND FORSKOLIN ONPROGESTERONE SECRETION BY PIG LUTEAL CELLS

The present study examined the effects of LH, prostaglandin E-2 (PGE(2 )), 8-bromo-cyclic AMP (cAMP) and forskolin on progesterone secretion by small and large pig luteal cells. Corpora lutea were isolated from, gilts (n greater than or equal to 3 per day) on days 9, 12 and 14 of t he oestrous cycle and days 9, 12, 14 and 30 of pregnancy. After enzyma tic dissociation of the corpora lutea, small and large luteal cells we re obtained by elutriation. Culture plates (24-well) were then seeded with 150 000 small luteal cells or 30 000 large luteal cells per well in 1 ml M199 medium in the absence or presence of LH, PGE(2), LH plus PGE(2), 8-bromo-cAMP or forskolin. After 12 h of incubation, culture p lates were centrifuged, and the supernatant collected and frozen for s ubsequent assay of progesterone. Differences within day were not detec ted between cyclic and pregnant gilts, and thus, results were combined for days 9, 12 and 14. Basal progesterone secretion by small luteal c ells was less (P < 0.05) on days 14 and 30 than days 9 and 12. Treatme nt with LH, PGE(2), 8-bromo-cAMP or forskolin increased (P < 0.05) pro gesterone se cretion by small luteal cells on days 9 and 12; however, treatments had no effect on days 14 and 30. Basal progesterone product ion by large luteal cells was less (P < 0.05) on day 30 compared with other days. PGE(2) stimulated (P < 0.001) progesterone production by l arge luteal cells at all days. In contrast, 8-bromo-cAMP and forskolin inhibited progesterone production by large luteal cells on day 12 (P < 0.05), and day 14 (P < 0.001). These data show that pregnancy status does not alter luteal cell response to the aforementioned secretagogu es. However, regulation of progesterone secretion differs between smal l and large luteal cells, and the age of the corpora lutea. Also, it i s unlikely that the stimulatory actions of PGE(2) involve increased cA MP production in pig large luteal cells.