Effect of PGF-2 alpha on progesterone production in swine luteal cells at different stages of the luteal phase

Progesterone and estradiol secretion by porcine luteal cells is influenced by individual and combined treatment with prostaglandins E2 and F2alpha throughout the estrus cycle

The present experiments were conducted to test whether the ratio of PGE2:PGF2alpha affects steroid secretion by porcine luteal cells. We examined the effect of separate and combined treatment with PGE2 and PGF2alpha on progesterone and estradiol secretion. Luteal cells were collected at three different stages of the luteal phase (1-3 days after ovulation; 10-12 days after ovulation and 14-16 days after ovulation). PGE2 alone in a dose dependent manner increased progesterone production by cells collected from mature corpora lutea. On the other hand, PGF2alpha in a dose dependent manner decreased progesterone secretion by cells of the same origin. Progesterone secretion by cells isolated from mature and regressing corpora lutea and treated with both prostaglandins increased in comparison to PGF2alpha-treated cultures. However, in cells collected from regressing corpora lutea PGE2 and PGF2alpha in a ratio of 2:1 and 4:1 increased estradiol production when compared to control and both ratios increased estradiol secretion in comparison to PGF2alpha-treated cells. These data 1) confirm the luteotropic effect of PGE2 and the luteolytic effect of PGF2alpha; 2) demonstrate that when the ratio of PGE2 to PGF2alpha changed from 1:1 to 2:1 or 4:1 cells were protected against the inhibitory effects of PGF2alpha on progesterone secretion by cells collected during the mid- and late luteal phase; and 3) suggest that elevated estradiol production by luteal cells, isolated during late luteal phase, under the influence of increased doses of PGE2 may serve as an additional source of estradiol to blastocysts, during early pregnancy in the pig.

In situ detection of apoptosis in regressing corpus luteum of pregnant sow: evidence of an early presence of DNA fragmentation

Luteolysis has been shown to be correlated with apoptosis in rats, sheep, and cows. In pigs, apoptosis has already been demonstrated as regards atretic follicles. The present study has been conducted to evaluate whether apoptosis occurs during corpora lutea regression in the pregnant pig and to investigate the temporal relationship between apoptosis and functional luteolysis. The apoptotic process has been studied through the research of oligonucleosome fragmentation by means of classical electrophoresis methods and by in situ detection on histological luteal sections. The latter method allows the identification of apoptosis and the localization of apoptotic cells. Pregnant sows were cloprostenol (PGF2 alpha analog) treated and ovariectomized 0, 6, 12, 24, 48, and 72 hr after treatment. Corpora lutea were utilized for progesterone and DNA extraction and in situ evaluation of apoptosis. Clear evidence of apoptosis was seen earlier with the in situ technique (6 hr for stromal tissue, 12 hr for luteal cells) than with the classical method (24 hr). Apoptosis was, however, apparent after plasma and tissue progesterone had reached basal levels. In conclusion, these results are consistent with the hypothesis that apoptosis occurs during luteolysis in pigs. Moreover, the data obtained with the in situ technique made it possible to identify signs of structural regression in stromal tissue first than in parenchymal cells. A two-stage activation of apoptosis has been discussed to explain structural changes that occur during luteolysis after cloprostenol treatment in swine corpora lutea.

Prostaglandin F2 alpha stimulates progesterone secretion by porcine luteal cells in vitro throughout the estrous cycle

In this study we examined the stimulatory effects of PGF2 alpha on progesterone secretion by porcine luteal cells on different days of the estrous cycle, and the effects of PGF2 alpha, A23187 and PMA on progesterone secretion by isolated large and small luteal cells, in vitro. Corpora lutea were obtained from cycling pigs (days 6-16), collagenase dispersed and luteal cells incubated in medium 199 in the absence or presence of increasing doses of PGF2 alpha, A23187, and PMA. Progesterone concentrations in spent media were measured by RIA. PGF2 alpha stimulation of progesterone secretion by mixed luteal cells did not vary significantly throughout the estrous cycle. Progesterone secretion by large, but not small, luteal cells was increased (p < 0.05) in a dose-dependent fashion by PGF2 alpha. A23187 also caused a dose-dependent increase in progesterone secretion by large luteal cells but inhibited small luteal cells. Progesterone secretion by both large and small luteal cells was significantly increased by increasing doses of PMA. We conclude that the stimulatory response of luteal cells to PGF2 alpha in vitro did not correlate with PGF2 alpha receptor concentrations (not measured in this study), and we speculate that calcium/protein kinase C may be involved in mediating the stimulatory action of PGF2 alpha on luteal cell progesterone secretion.

Lipopolysaccharide-induced increases in porcine serum cortisol and progesterone concentrations are not mediated solely by prostaglandin F2 alpha

The increase in steroid hormone blood levels in response to bacterial lipopolysaccharide (LPS) appears to be an important mechanism by which mammalian species regulate inflammation. This study examined changes in serum concentrations of cortisol, progesterone, and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in diestrous pigs following the intravenous injection of LPS and determined whether indomethacin would attenuate these changes. Serum cortisol and progesterone concentrations increased (P < 0.05) within 30 min after the administration of LPS, and the increases in steroid hormones were accompanied by a sharp, transient increase (P < 0.05) in PGFM levels. In the presence of indomethacin, serum PGFM levels did not change (P > 0.05); however, LPS enhanced (P < 0.05) cortisol and progesterone concentrations, although the increases were delayed. Serum concentrations of cortisol acutely increased (P < 0.05) immediately following both infusions of indomethacin. In summary, cortisol and progesterone concentrations increased irrespective of serum PGFM concentrations, thereby indicating that prostaglandin F2 alpha was not the sole mediator of LPS-induced changes in cortisol and progesterone concentrations.

Acute stimulatory effects of prostaglandin F2 alpha on serum progesterone concentrations in pregnant and pseudopregnant pigs

The objective of this study was to investigate whether PGF2 alpha, administered to pregnant and pseudopregnant gilts in vivo, would cause an acute increase in serum progesterone concentrations prior to luteolysis. Pregnant (n = 9) and pseudopregnant (n = 4) gilts were fitted with a jugular vein cannula on day 40, were treated with 3 ml vehicle (control) i.m. on day 42 and with 15 mg PGF2 alpha on day 45. Blood samples were collected at frequent (5 and 15 min) intervals from 1 h before until 1 h after control and PGF2 alpha injections, at 15 min intervals for 4 h, and then at 5, 6, 9, 21, 33, 45 and 57 h post injection. Progesterone was measured by radioimmunoassay (RIA) in all samples. Porcine LH was measured by RIA in samples collected frequently in the 1 h pre- and 1 h post-injection periods. Serum progesterone concentrations were unchanged in both pregnant and pseudopregnant animals in response to control injection on day 42. However, in both pregnant and pseudopregnant gilts, PGF2 alpha injection on day 45 resulted in an acute increase (approximately 75-80% above pre-treatment levels; p less than 0.05) in serum progesterone lasting approximately 1 h, followed by a return to pre-treatment levels by 2 h, and then a decline to 1 ng/ml or less by 45-57 h (pregnant) or 21-57 h (pseudopregnant), associated with luteolysis. Serum LH concentrations were unchanged between 1 h pre- and post-treatment periods in response to either control or PGF2 alpha-treatment, in both pregnant and pseuodpregnant gilts. These results indicate that PGF2 alpha-injection produces a rapid and transient increase in serum progesterone concentrations which may result from a rapid and direct stimulatory action of PGF2 alpha on porcine luteal cell progesterone synthesis/secretion in vivo.

In vitro action of PG F2 alpha on progesterone and cAMP synthesis in small bovine luteal cells

The action of prostaglandin F2 alpha (PG F2 alpha) on incubated small bovine luteal cells in the presence or in the absence of bovine luteinizing hormone (LH) or dibutyryl cyclic adenosine monophosphate (db cAMP) was investigated. In the absence of LH and db cAMP, PG F2 alpha stimulated progesterone synthesis at concentrations of 10 ng/ml and 100 ng/ml but had no effects at concentrations below 1 ng/ml. PG F2 alpha partially inhibited the LH or db cAMP stimulated progesterone synthesis. This inhibition was maximal for PG F2 alpha concentrations around 100 pg/ml whereas distinctly higher or lower concentrations were without effect. At the concentration of 100 pg/ml, PG F2 alpha partially inhibited the LH induced cAMP accumulation. These results demonstrate an "in vitro" action of PG F2 alpha on bovine luteal cells. They indicate that the luteolytic action of PG F2 alpha in the bovine species could involve, as already suggested for the rat, both an inhibition of the LH induced synthesis of cAMP and an inhibition of the action of cAMP.