Effect of prostaglandin E2 alpha on the hCG-stimulated progesterone production by human corpora lutea

Effects of Nicotine on Human Luteal Cells In Vitro: A Possible Role on Reproductive Outcome for Smoking Women1

We investigated the effect of nicotine and its methylated metabolite, N-methyl-nicotine (M-nicotine), on human luteal cells by measuring release of progesterone and prostaglandins (PGs) from cultured cells and by testing gene expression of vascular endothelial growth factor (VEGF), an angiogenic factor strictly involved in luteal pathophysiology. Primary cultures of human luteal cells were treated for 24 h with nicotine and M-nicotine (from 10(-6) to 10(-11) M) either alone or combined with hCG (25 ng/ml); progesterone and PGs were assayed in the culture medium. In another group of experiments, luteal cells were treated for 24 h with nicotine and M-nicotine (10(-7) M) to perform reverse transcriptase-polymerase chain reaction on VEGF mRNA. Nicotine and M-nicotine negatively affected basal luteal steroidogenesis at all tested concentrations, but neither was able to affect hCG-induced progesterone release. Both substances were able to significantly increase PGF2alpha release from luteal cells, with a dose-related efficacy for M-nicotine. On the contrary, PGE2 release was significantly inhibited by both nicotine and its metabolite. Finally, nicotine was able to increase VEGF mRNA expression significantly, whereas M-nicotine was not. In conclusion, nicotine and M-nicotine can induce a sort of luteal insufficiency by inhibiting progesterone release, probably through modulation of the PG system.

Endothelins enhance prostaglandin (PGE(2) and PGF(2alpha)) biosynthesis and release by human luteal cells: evidence of a new paracrine/autocrine regulation of luteal function

We have previously shown that endothelin-1 (ET-1) is normally found in human luteal cells, where it is able to significantly inhibit both basal and hCG-induced progesterone production. To further expand our comprehension of the possible roles of endothelins (ETs) in luteal physiology, in this study we used primary cultures of luteal cells exposed to graded doses of ET-1 and ET-3; PGF(2alpha) and PGE(2) were assayed in the culture medium to investigate whether ETs also influence cyclooxygenase activity in these cells. We found that both ETs are able to significantly stimulate PGF(2alpha) and PGE(2) release in a dose- and time-dependent manner. ET-1 was always more effective than ET-3. Experiments with two endothelin receptor antagonists (the BQ485 and BQ788 compounds, which block the ET-A and ET-B receptors, respectively) showed that the two endothelins induce PG production through different receptors and signaling pathways. In conclusion, here we demonstrate the ability of ETs to influence PG synthesis and release from human luteal cells. As PGs are deeply involved in corpus luteum activity, and ETs were also able to influence progesterone production, the present new data suggest an interesting interplay among progesterone, PGs, and ETs in the control of corpus luteum physiology.

Auto/paracrine role of prostaglandins in corpus luteum function

The homeostasis and ephemerality of the corpus luteum (CL) involves an intriguing interplay amongst pituitary, placental and intraovarian regulators. Recent findings have indicated a local pathway of synthesis for the cyclooxygenase-derived prostaglandins (PGs) in luteal cells of all mammalian species investigated. Thus, an autocrine or paracrine role of intraluteal PGs in modulation of luteal steroidogenesis is implicated. The presence of immune cells in the ovary indicates a constitutive role of these cells and their secretory products, in particular the cytokines, some of which have been demonstrated to greatly influence luteal PG and progesterone production. Despite the plentitude of investigations, a precise role for PGs other than PGF2 alpha in regulation of CL function is still obscure, mainly lacking evidence of cell-specific expression of various classes of PG receptors and their intracellular signaling mechanisms.

Mode of action of prostaglandin F2 alpha in human luteinized granulosa cells: role of protein kinase C

It is well documented that prostaglandin F2 alpha (PGF2 alpha) inhibits progesterone production in luteal cells, but its mode of action is uncertain. It has recently been suggested that PGF2 alpha acts by activating the calcium and phospholipid-dependent protein kinase, protein kinase C (PKC). This hypothesis has been tested by comparing the site and mode of action of PGF2 alpha, a PGF2 alpha analogue (cloprostenol) and the PKC activator phorbol myristate acetate (4 beta PMA) in human granulosa-lutein cells. PGF2 alpha and cloprostenol exerted similar concentration-dependent inhibitory actions on gonadotrophin-stimulated cyclic AMP (cAMP) accumulation and progesterone production by human granulosa-lutein cells. The similarity in the actions of PGF2 alpha and cloprostenol in human granulosa-lutein cells suggests that they can be used interchangeably to study the role of PGF2 alpha in the regulation of steroidogenesis in the human ovary. Gonadotrophin-stimulated cAMP accumulation and progesterone production was also concentration-dependently inhibited by 4 beta PMA. In addition, cloprostenol and 4 beta PMA also inhibited dibutyryl cAMP-stimulated progesterone production, suggesting that these compounds inhibit LH action at sites before and after the generation of cAMP. The pre-cAMP site of action can be localised to the stimulatory G-protein (Gs) as both compounds inhibited cholera toxin-stimulated cAMP accumulation without affecting forskolin-stimulated cAMP accumulation. The post cAMP site of action can be localised to actions on cholesterol side chain cleavage enzyme, as both cloprostenol and 4 beta PMA inhibited 22R hydroxycholesterol-supported progesterone production without affecting pregnenolone-supported progesterone production. The finding that cloprostenol and 4 beta PMA interact with the steroidogenic cascade in a similar manner is indicative of a shared common mediator of their actions in human granulosa-lutein cells, i.e. PKC. The inhibitory actions of PGF2 alpha and 4 beta PMA on hLH-stimulated progesterone production were abolished in the presence of the PKC inhibitor, staurosporine. In addition, in PKC-depleted cells (achieved by exposure to 4 beta PMA for 20 h) the inhibitory actions of PGF2 alpha and 4 beta PMA were abolished. These results support the hypothesis that the inhibitory actions of PGF2 alpha are mediated by PKC in human granulosa-lutein cells.

Prostaglandin F2 alpha stimulates cAMP phosphodiesterase via protein kinase C in cultured human granulosa cells

To investigate the involvement of cyclic AMP phosphodiesterase in the antigonadotrophic actions of prostaglandin F2 alpha (PGF2 alpha), human granulosa cells were cultured in serum-supplemented medium for 72 h, treated for 30 min with cloprostenol or phorbol myristate acetate (PMA) and then exposed to human chorionic gonadotrophin (hCG) +/- isobutyl-methylxanthine (IBMX) for a further 4 h. In the absence of IBMX, cloprostenol and PMA inhibited hCG-stimulated progesterone production. However, in the presence of 0.5 mM IBMX, inhibition of phosphodiesterase prevented these antigonadotrophic effects. Phosphodiesterase activity was assessed by a novel direct assay performed on intact cells after 3 days of culture. PGF2 alpha, cloprostenol and 4 beta-PMA all enhanced cAMP degradation whilst an inactive phorbol ester (4 alpha-PMA) had no effect. Down-regulation of protein kinase C by 4 beta-PMA pre-treatment prevented the subsequent stimulation of phosphodiesterase activity by both cloprostenol and 4 beta-PMA. We conclude that the antigonadotrophic actions of PGF2 alpha in cultured human granulosa cells involve a stimulation of cAMP phosphodiesterase mediated via protein kinase C.

The enzymes in cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism in human corpora lutea: dependence on luteal phase, cellular and subcellular distribution

Eicosanoids synthesized within corpus luteum are presumed to regulate luteal function in women. However, the potential cellular source(s) of the eicosanoids, whether small and large luteal cells differ in eicosanoid synthesis and whether eicosanoids other than prostaglandin (PG)E2, PGF2 alpha and 6-keto-PGI1 alpha can be synthesized, have not been investigated. The present immunocytochemical studies were undertaken to answer these questions using mono and polyclonal antibodies to several enzymes in arachidonic acid metabolism by cyclooxygenase and lipoxygenase pathways. Human corpora lutea from early (n = 5), mid (n = 6) and late (n = 3) luteal phases were specifically immunostained for all the enzymes. All the enzymes were present in small and large luteal cells as well as in non luteal cells. However, small luteal cells contained more immunoreactive 5-lipoxygenase, PGD2 and PGF2 alpha synthases; large luteal cells contained more TXA2 synthase and 12-lipoxygenase; small and large luteal cells contained similar amounts of cyclooxygenase and PGI2 synthase. In all the cells, immunoreactive PGD2, PGI2 and TXA2 synthases increased from early to mid luteal phase and then declined in late luteal phase. Cyclooxygenase, 5- and 12-lipoxygenases and PGF2 alpha synthase, on the other hand, increased from early to mid and mid to late luteal phases. Immunoreactive cyclooxygenase and 5- and 12-lipoxygenases were present primarily in rough endoplasmic reticulum (ER) and/or smooth ER and cytoplasm. Quite unexpectedly, all three enzymes were also found in nuclear membranes, condensed chromatin and especially at the perimeter of condensed chromatin. Dispersed chromatin contained very little or no immunoreactive enzyme. These results indicate that regulation of human luteal function by eicosanoids synthesized within the corpus luteum is complex involving perhaps a) small and large luteal as well as non luteal cells, b) eicosanoids which have not been previously considered to play a role in luteal function and c) coordinate regulation of more than one enzyme in the pathways of arachidonic acid metabolism.

Corpus luteum: animal models of possible relevance to reproductive toxicology

The presence of a normally functioning corpus luteum is an essential requirement for the maintenance of gestation in mammals. The chief function of the corpus luteum in all species is to synthesize the steroid hormone progesterone that is necessary for implantation and for the subsequent development of the fetoplacental unit. Activation and maintenance of luteal function involve pituitary, placental, and ovarian hormones. Perturbation in the secretion and/or action of any of these luteotropins by exogenous compounds can profoundly affect the steroidogenic capacity of the corpus luteum. Abnormal luteal function causes failure of implantation and embryonic wastage. Both in vitro and in vivo models for assessing luteal function are available; while the former are more convenient, the model of choice for toxicological studies is one in which in vitro findings can be easily confirmed in whole animals in vivo. This article is concerned primarily with the techniques used in basic research that might be useful for the evaluation of luteal function in reproductive toxicology.

Luteal phase variations in endogenous concentrations of prostaglandins PGE and PGF and in the capacity for their in vitro formation in the human corpus luteum

One evidence for a luteolytic role for prostaglandin F2 alpha in the human is the increase in luteal PGF at times corresponding to luteolysis as reported earlier by us and other groups. There have been other contradictory reports on this point. In the present experiments we have measured the concentrations of PGE and PGF in 16 more human corpora lutea and have determined the capacity of those tissues to form PGE and PGF in vitro. PGF concentrations were highest in the mid luteal phase but were accompanied by high PGE concentrations. On the other hand, in the late luteal phase PGF concentrations, lower than in mid luteal but generally higher than in early luteal phase, were significantly higher than PGE concentrations. This pattern in PGE and PGF concentrations was also evident in the capacity of these tissues to form these compounds in vitro. In view of the known capacity of PGE2 to counteract the luteolytic effect of PGF2 alpha, these variations in the relative concentrations of PGE and PGF during the luteal phase may be of significance in the process of luteolysis in the human.