Effects of LH, prostaglandin E2, 8-bromo-cyclic AMP and forskolin on progesterone secretion by pig luteal cells.

The present study examined the effects of LH, prostaglandin E2 (PGE2), 8-bromo-cyclic AMP (cAMP) and forskolin on progesterone secretion by small and large pig luteal cells. Corpora lutea were isolated from gilts (n > or = 3 per day) on days 9, 12 and 14 of the oestrous cycle and days 9, 12, 14 and 30 of pregnancy. After enzymatic dissociation of the corpora lutea, small and large luteal cells were 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, PGE2, LH plus PGE2, 8-bromo-cAMP or forskolin. After 12 h of incubation, culture plates were centrifuged, and the supernatant collected and frozen for subsequent assay of progesterone. Differences within day were not detected between cyclic and pregnant gilts, and thus, results were combined for days 9, 12 and 14. Basal progesterone secretion by small luteal cells was less (P < 0.05) on days 14 and 30 than days 9 and 12. Treatment with LH, PGE2, 8-bromo-cAMP or forskolin increased (P < 0.05) progesterone secretion by small luteal cells on days 9 and 12; however, treatments had no effect on days 14 and 30. Basal progesterone production by large luteal cells was less (P < 0.05) on day 30 compared with other days. PGE2 stimulated (P < 0.001) progesterone production by large 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 secretagogues. However, regulation of progesterone secretion differs between small and large luteal cells, and the age of the corpora lutea. Also, it is unlikely that the stimulatory actions of PGE2 involve increased cAMP production in pig large luteal cells.