Effect of human chorionic gonadotropin and prostaglandin F2a on progesterone production by human luteal cells

Lipidomics and plasma hormone analysis differentiate reproductive and pregnancy statuses in Florida manatees (Trichechus manatus latirostris)

Florida manatees (Trichechus manatus latirostris) are protected as a threatened species, and data are lacking regarding their reproductive physiology. This study aimed to (1) quantify plasma steroid hormones in Florida manatees from two field sites, Crystal River and Indian River Lagoon, at different gestational stages and to (2) identify individual lipids associated with pregnancy status. Ultra-high performance liquid chromatography-tandem mass spectrometric analysis was used to measure plasma steroid hormones and lipids. Pregnant female manatees were morphometrically distinct from male and non-pregnant female manatees, characterized by larger body weight and maximal girth. Progesterone concentrations in manatees were also elevated during early gestation versus late gestation. Cholesterol, an important metabolic lipid, and precursor for reproductive steroids, was not different between groups. Mass spectrometry quantified 949 lipids. Plasma concentrations of glycerophospholipids, glycerolipids, sphingolipids, acylcarnitines, and cholesteryl esters were associated with pregnancy status in the Florida manatee. Most of the lipid species associated with pregnancy were triacylglycerides, phosphatidylethanolamines, and ether-linked phosphatidylethanolamines, which may serve as energy sources for fetal development. This research contributes to improving knowledge of manatee reproductive physiology by providing data on plasma steroid hormones relative to reproductive status and by identifying plasma lipids that may be important for pregnancy. Elucidation of lipid species directly associated with pregnancy has the potential to serve as a diagnostic approach to identify pregnant individuals in fresh and archived samples. These biochemical and morphometric indicators of reproductive status advance the understanding of manatee physiology.

Corpus luteum function and regression

Several conclusions can be drawn from a review of the formation, function and regression of the corpus luteum. Ovulation and luteinization encompass degenerative and growth changes. Inflammatory conditions associated with ovulation lead to the breakdown of the follicle wall and the membrana granulosa, along with initial damage to theca and granulosa cells. The early corpus luteum is, therefore, a tissue in stress. Thus, one view of the corpus luteum is that it, like the phoenix, rises from the inflammatory ashes of the postovulatory follicle to exist briefly and to be consumed by a similar process at regression. The luteinization process is associated with parenchymal cell hypertrophy and matrix remodelling, which appear to be regulated by IGFs and androgens, and with angiogenesis, which is induced mostly by bFGF. High levels of functional activity of the corpus luteum are regulated by control at the level of the LH receptor, whose activation leads to the translocation of cholesterol into the cell and mitochondria for conversion to steroids. Functional luteal regression can be considered as another inflammatory-like condition with apparent activation of the immune system, along with cytokine, reactive oxygen, and eicosanoid production. Structural luteolysis is subsequently invoked that leads to matrix dissolution and cellular degeneration. It is perhaps not surprising that the invocation of immune activation, which causes the production of DNA-damaging reactive oxygen species and cytotoxic cytokines each cycle, may increase the risk of pathologies. One example may be ovarian cancer which appears to be associated with the use of fertility-enhancing drugs and associated with the number of ovulations in a woman's lifetime.

Effect of the oxytocin antagonist antocin and agonist decomoton on baboon luteal cell production and release of progesterone

OBJECTIVE

To evaluate the effect of oxytocin, its antagonist antocin, and agonist decomoton on baboon luteal cell P secretion.

DESIGN

Prospective study.

SETTING

Academic department of obstetrics and gynecology in a US medical school.

ANIMAL(S)

Luteal-phased timed corpora lutea (CL) from a cohort of adult cycling baboons (Papio anubis).

INTERVENTION(S)

Dispersed luteal cells from luteal phase baboon CL were cultured and treated with nothing (control), oxytocin (4-400 mU), antocin (4-400 microg), oxytocin with antocin, decomoton (4-400 microg), or oxytocin with decomoton.

MAIN OUTCOME MEASURE(S)

Basal and hCG (10 U)-stimulated P were measured in the incubate.

RESULT(S)

Basal P secretion did not change significantly with all peptides studied. The hCG-stimulated P secretion was significantly inhibited by oxytocin (4-400 mU), antocin (4-400 microg), and antocin combined with oxytocin, and with oxytocin, decomoton, and decomoton combined with oxytocin. Antocin (-12%) was less inhibitory than oxytocin (-25% to -22%). Antocin combined with oxytocin enhanced the inhibition to -35% to -39%. Decomoton had stronger (not significant) inhibition than oxytocin. Mean inhibition was 28%-35% with all doses of oxytocin, decomoton, or combined together.

CONCLUSION(S)

Although decomoton, an oxytocin agonist inhibited hCG-stimulated luteal cell P secretion in vitro, antocin also acted like an agonist, rather than an antagonist, in inhibiting P secretion.

Stepwise activation of the gonadotropic signal transduction pathway, and the ability of prostaglandin F2alpha to inhibit this activated pathway

Through selective activation of the gonadotropic signal transduction pathway, we have determined the probable site of the antigonadotropic effects of prostaglandin F2alpha (PGF2alpha) in the human granulosa-luteal cell (hGLC). The gonadotropic signal transduction pathway was activated at the level of the receptor (luteinizing hormone and beta-adrenergic), stimulatory G protein (Gs), adenylate cyclase (AC), and protein kinase A (PKA) by human chorionic gonadotropin (hCG) and isoproterenol (Iso), cholera toxin (CTX), forskolin, and dibutryl cAMP (Db cAMP), respectively. Concomitantly, the ability of PGF2alpha to inhibit progesterone production in response to the activation of this cascade at these different levels was examined. hGLCs were obtained from in vitro fertilization patients and were precultured for 8 d in Medium 199 supplemented with fetal bovine serum (M199; 10% FBS). Following the preculture period, cells were treated with either vehicle or one of the above activators of the gonadotropic pathway, either in the absence or presence of PGF2alpha (in M199; No FBS). Following the treatment period, media were collected and assayed for progesterone by RIA. Prostaglandin F2alpha (10(-6) M) significantly inhibited hCG (1 IU/mL), Iso (10(-5) M), CTX (1 microg/mL), and forskolin- (10(-5) M) stimulated progesterone production. Conversely, PGF2alpha did not inhibit progesterone production stimulated by a saturating concentration of Db cAMP (10(-6) M). The ability of PGF2alpha to inhibit hCG- or CTX-stimulated progesterone production was attenuated by pertussis toxin (PTX; 50 ng/mL). In conclusion, through a pertussis toxin-sensitive G protein, PGF2alpha inhibits progesterone production at a level below AC, and above the activation of PKA by cAMP.

In vitro microdialysis of baboon corpus luteum: effects of oxytocin on total and pulsatile progesterone secretion

Baboon corpora lutea (two each from the early, mid- and late luteal phases) were individually microretrodialyzed in vitro for 48 h, 12 h initial baseline, 12 h retrodialysis with OT (9 mU/h), 12 h without OT and 12 h with cAMP (5 mmol/h). Progesterone (P) was measured by a sensitive and specific radioimmunoassay in 10-min fractions of retrodialysates and analyzed for P peaks by PC-pulsar 3.0. Neither OT nor cAMP had any effect on the characteristics of P pulses. In early and late luteal phase CL, OT inhibited P secretion within 1 h of administration followed by increased P secretion late during OT perfusion. In midluteal phase, OT did not affect P secretion. In all CL, P secretion was sustained or further increased during the 12 h after stopping OT. cAMP also sustained baseline or stimulated P secretion. In contrast, OT either increased total P output/12 h (28 to 49% above baseline) with a further increase of 21% to 296% above baseline after stopping OT, or inhibited total P output by 4% to 13% percent with a further decline of 51% to 61% after stopping OT. Thus, while overall OT is luteotropic, its dual effect (initial inhibition followed by stimulation) suggests direct and indirect effects through paracrine-autocrine mechanisms.

The effects of gonadotropin on the phosphatidylinositol pathway in the primate corpus luteum

The current study was designed to investigate the effects of gonadotropin on basal and prostaglandin (PG) F2 alpha-induced activity of the phosphatidylinositol pathway in corpora lutea (CL) of rhesus monkeys. Luteal progesterone production in vitro was significantly stimulated (P < 0.05) by human chorionic gonadotropin (hCG). Neither basal nor PGF2 alpha-induced phosphatidylinositol 4,5-bisphosphate hydrolysis was significantly influenced by hCG in CL of various ages (P > 0.10). Gonadotropin did induce a slight, yet sustained, increase (P < 0.05) in [Ca2+]i in approximately 70% of luteal cells. The maximal increase in [Ca2+]i in response to hCG (approximately 100 nM) was about one-tenth that induced by PGF2 alpha (approximately 1000 nM). hCG treatment did not alter (P > 0.10) the increase in [Ca2+]i induced by PGF2 alpha Treatment-induced changes in [Ca2+]i did not differ between small (17-21 microns) and large (23-28 microns) luteal cells. Therefore, luteolytic agents are more potent activators of the phosphatidylinositol pathway than luteotropins. This is consistent with the hypothesis that the phosphatidylinositol pathway is involved in primate luteal regression. The inability of hCG to acutely alter the responsiveness of this pathway to PGF2 alpha suggests that CG may rescue the CL of early pregnancy via a mechanism other than direct inhibition of the luteolytic actions of PGF2 alpha.

Effects of oestrogen on progesterone synthesis and arachidonic acid metabolism in human luteal cells

OBJECTIVE

Locally produced oestrogens and prostaglandins (PGs) are implicated in the regulation of luteal lifespan in the human ovary. This study (1) assesses direct effects of these factors on progesterone synthesis in isolated luteal cells, and (2) explores interactions between luteal age and treatment with gonadotrophin or oestrogen on the metabolism of arachidonic acid (prostaglandin precursor) by steroidogenic luteal cells in vitro.

DESIGN

Primary monolayer cultures of human luteal cells obtained at different stages of the luteal phase were used to investigate the effect of oestradiol, catechol oestrogens (2- and 4-hydroxyoestradiol), diethylstilboestrol, PGE2 and PGF2 alpha on basal and human chorionic gonadotrophin (hCG) stimulated progesterone production in vitro. The role of PGs as modulators of luteal cell function was further investigated by studying the metabolic fate of radioactively labelled arachidonic acid in hormone treated (oestradiol and hCG) and control cultures, assessed by high performance liquid chromatography.

PATIENTS

Corpora lutea were enucleated from nine women with regular ovulatory cycles undergoing microsurgical reversal of tubal sterilization. Granulosa cell aspirates were obtained from three patients undergoing in-vitro fertilization treatment.

RESULTS

PGE2 and PGF2 alpha at various concentrations did not have a consistent effect, whereas oestradiol, diethylstilboestrol (and 2-hydroxyoestradiol in early luteal cell cultures) significantly inhibited basal and hCG stimulated progesterone biosynthesis. Evidence for direct inhibition of 3 beta-hydroxysteroid dehydrogenase enzymic activity by oestradiol was obtained. Both major metabolic pathways of arachidonic acid (lipoxygenase and cyclo-oxygenase) were operative in steroidogenic luteal cells recovered throughout the luteal phase. The ratio of PGE2 to PGF2 alpha synthesis in vitro by human luteal cells from endogenously incorporated arachidonic acid did not change significantly with corpus luteum age, with PGE2 tending to predominate. Oestradiol treatment shifted arachidonic acid metabolism from the lipoxygenase towards the cyclooxygenase pathway in cells isolated from ageing corpora lutea.

CONCLUSIONS

Oestradiol, at relatively high concentrations, is a potent inhibitor of basal and hCG induced luteal cell steroidogenesis in vitro. No support is provided for the concept that luteolysis is mediated by local production of PGF2 alpha. The putative luteolytic effect of oestradiol may entail reduced metabolism of arachidonic acid to lipoxygenase derived products by luteal cells rather than direct stimulation of prostaglandin production by itself.