The luteotrophic actions of prostaglandins E2 and F2 alpha on dispersed marmoset luteal cells are differentially mediated via cyclic AMP and protein kinase C

The interplay between bioactive sphingolipids and steroid hormones

Steroid hormones regulate various physiological processes including development, reproduction, and metabolism. These regulatory molecules are synthesized from cholesterol in endocrine organs - such as the adrenal glands and gonads - via a multi-step enzymatic process that is catalyzed by the cytochrome P450 superfamily of monooxygenases and hydroxysteroid dehydrogenases. Steroidogenesis is induced by trophic peptide hormones primarily via the activation of a cAMP/protein kinase A (PKA)-dependent pathway. However, other signaling molecules, including cytokines and growth factors, control the steroid hormone biosynthetic pathway. More recently, sphingolipids, including ceramide, sphingosine-1-phosphate, and sphingosine, have been found to modulate steroid hormone secretion at multiple levels. In this review, we provide a brief overview of the mechanisms by which sphingolipids regulate steroidogenesis. In addition, we discuss how steroid hormones control sphingolipid metabolism. Finally, we outline evidence supporting the emerging role of bioactive sphingolipids in various nuclear processes and discuss a role for nuclear sphingolipid metabolism in the control of gene transcription.

The relationship between the production and the anti-gonadotrophic action of prostaglandin F 2 alpha in luteal cells from the marmoset monkey (Callithrix jacchus) in the early and mid-luteal phase

To address the potential luteolytic role for prostaglandin F(2 alpha) (PGF(2 alpha)) in the corpus luteum of the common marmoset monkey (Callithrix jacchus), the ability of marmoset luteal cells, maintained in monolayer culture, to produce PGF(2 alpha) was determined in vitro in the presence and absence of human chorionic gonadotrophin (hCG) and other established pharmacological modulators of PGF(2 alpha) synthesis. We also assessed the effects of the PGF(2 alpha) analogue, cloprostenol, on progesterone output from luteal cells isolated in the early luteal phase versus the mid-luteal phase (days 3 and 14 post ovulation, respectively). Cloprostenol had no effect on progesterone output from luteal cells isolated on day 3 of the luteal phase, whereas it significantly inhibited both basal and hCG-stimulated progesterone synthesis by day 14 luteal cells during the culture period 48-72 h (P<0.001). Intra-luteal PGF(2 alpha) concentrations were 5-fold higher in luteal cells isolated in the early luteal phase than in mid-luteal phase cells (16.5+/-3.5 versus 3.5+/-0.6 pmol/10(5) cells). While PGF(2 alpha) production was unaffected by hCG in vitro, it was decreased by indomethacin (1000 ng/ml) (P<0.05) and stimulated by the calcium ionophore A23187 (10 micromol/l) (P<0.05) in luteal cells from both stages of the luteal phase. Phospholipase A(2) did not influence PGF(2 alpha) production by day 3 luteal cells whereas at 10 IU/ml, it significantly stimulated PGF(2 alpha) production by day 14 luteal cells (P<0.05). Hence, the timing of luteolysis in the common marmoset monkey appears to involve changes in both the luteal cell response to and production of PGF(2 alpha).

PTGER1 and PTGER2 receptors mediate regulation of progesterone synthesis and type 1 11beta-hydroxysteroid dehydrogenase activity by prostaglandin E2 in human granulosa lutein cells

In luteinizing granulosa cells, prostaglandin E(2) (PGE(2)) can exert luteotrophic actions, apparently via the cAMP signalling pathway. In addition to stimulating progesterone synthesis, PGE(2) can also stimulate oxidation of the physiological glucocorticoid, cortisol, to its inactive metabolite, cortisone, by the type 1 11beta-hydroxysteroid dehydrogenase (11betaHSD1) enzyme in human granulosa-lutein cells. Having previously shown these human ovarian cells to express functional G-protein coupled, E-series prostaglandin (PTGER)1, PTGER2 and PTGER4 receptors, the aim of this study was to delineate the roles of PTGER1 and PTGER2 receptors in mediating the effects of PGE(2) on steroidogenesis and cortisol metabolism in human granulosa-lutein cells. PGE(2)-stimulated concentration-dependent increases in both progesterone production and cAMP accumulation (by 1.9 +/- 0.1- and 18.7 +/- 6.8-fold respectively at 3000 nM PGE(2)). While a selective PTGER1 antagonist, SC19220, could partially inhibit the steroidogenic response to PGE(2) (by 55.9 +/- 4.1% at 1000 nM PGE(2)), co-treatment with AH6809, a mixed PTGER1/PTGER2 receptor antagonist, completely abolished the stimulation of progesterone synthesis at all tested concentrations of PGE(2) and suppressed the stimulation of cAMP accumulation. Both PGE(2) and butaprost (a preferential PTGER2 receptor agonist) stimulated concentration-dependent increases in cortisol oxidation by 11betaHSD1 (by 42.5 +/- 3.1 and 40.0 +/- 3.0% respectively, at PGE(2) and butaprost concentrations of 1000 nM). Co-treatment with SC19220 enhanced the ability of both PGE(2) and butaprost to stimulate 11betaHSD1 activity (by 30.2 +/- 0.2 and 30.5 +/- 0.6% respectively), whereas co-treatment with AH6809 completely abolished the 11betaHSD1 responses to PGE(2) and butaprost. These findings implicate the PTGER2 receptor-cAMP signalling pathway in the stimulation of progesterone production and 11betaHSD1 activity by PGE(2) in human granulosa-lutein cells.

Roles for prostaglandins in the steroidogenic response of human granulosa cells to high-density lipoproteins

In human granulosa-lutein cells, high-density lipoproteins (HDL) can stimulate progesterone synthesis. The objective of the present study was to establish whether prostaglandins (PGs) participate in the steroidogenic response to HDL. Both HDL and apolipoprotein AI (ApoAI) stimulated concentration-dependent increases in PGE2, cAMP and progesterone accumulation. The minimum concentrations of HDL and ApoAI required to elevate PGE2 production were the same as those required to stimulate cAMP accumulation and progesterone synthesis. Concentrations of PGE2 were elevated within 10 min in cells exposed to HDL and rose progressively over 24 h, whereas cAMP and progesterone were only increased significantly after 24 h of treatment with HDL. Co-treatment with prostaglandin H synthase inhibitors (meclofenamic acid and indomethacin) abolished the cAMP and progesterone responses to both HDL and ApoAI. Hence, the ability of HDL to stimulate progesterone synthesis can be mimicked by ApoAI and appears to involve increased generation of one or more luteotrophic PGs, possibly acting via cAMP.

The lipoxygenase pathways are involved in LH-stimulated progesterone production in bovine corpus luteum

We have examined the effects of endogenous lipoxygenase products on basal progesterone (P4) production by cultured bovine mid-luteal cells. The involvement of lipoxygenase products in the stimulatory effect of LH on luteal cAMP accumulation and P4 production was also examined. Bovine luteal cells from mid-cycle corpora lutea (CL) were exposed for 16 h to a lipoxygenase inhibitor (nordihydroguaiaretic acid: NDGA; 0.33-33 microM). For the last 4 h of incubation, the cells were exposed to LH and/or three different lipoxygenase products, 5-, 12- and 15-hydroxyeicosatetraenoic acid (HETE). NDGA inhibited P4 production by the cells in a dose-dependent manner (P < 0.05). NDGA-reduced P4 production was reversed by the addition of 12-HETE, but not 5- or 15-HETE, whereas 5-, 12- and 15-HETE alone showed no significant effect on P4 production in the intact cells. Furthermore, NDGA (33 microM) blocked the stimulatory action of LH on P4 production (P < 0.05), without changing cAMP accumulation (P > 0.1). When the cells were exposed to 5-, 12- or 15-HETE with LH and NDGA, only 15-HETE maintained the stimulatory effect of LH on P4 production in the cells (P < 0.05). These results suggest that endogenous lipoxygenase products play important roles in P4 production by bovine CL, i.e. basal P4 production is supported by 12-HETE, and LH-stimulated P4 production is partially mediated via the activation of lipoxygenase and subsequent 15-HETE formation downstream of the LH-activated cAMP-PKA-phosphorylation pathway.

Human granulosa-lutein cells express functional EP1 and EP2 prostaglandin receptors

Prostaglandin E(2) (PGE(2)) exerts mainly luteotrophic effects in the corpus luteum. In other tissues, PGE(2) acts via specific PGE(2) receptor subtypes including EP1, which modulates intracellular calcium ([Ca(2+)](i)) and EP2, which is coupled to cyclic AMP (cAMP) generation. We have therefore investigated the presence of functional EP1 and EP2 receptors using human granulosa-lutein (GL) cells. Reverse-transcription PCR revealed that GL cells expressed mRNA transcripts encoding both EP1 and EP2 receptors. When GL cells were challenged with ligands that can bind to both receptor subtypes (PGE(2) and 16,16 dimethyl PGE(2)) or exclusively to EP2 (butaprost), both cAMP formation and progesterone synthesis were stimulated. Furthermore, the cAMP response to these agonists could be significantly blocked by an EP1/2 antagonist AH6809 but not by an EP1-selective antagonist SC19220. Exposure of GL cells to 16,16-dm PGE(2) transiently raised [Ca(2+)](i) levels, which could be prevented by both AH6809 and SC19220. We therefore conclude that human GL cells express functional EP1 and EP2 receptors.

Effects of altering dietary fatty acid composition on prostaglandin synthesis and fertility

Several studies over the past 20 years have demonstrated that subjects on diets composed of substances with high levels of n-3 polyunsaturated fatty acids (PUFAs) (e.g. fish) have a decreased incidence of heart disease. On this basis, a recent report from the Department of Health has advised UK consumers to decrease the proportion of saturated as opposed to unsaturated fats in their diet and to increase the ratio of n-3 to n-6 PUFAs. This could be achieved by altering the amounts of these constituents in milk and meat. n-3 Fatty acids can most easily be added to animal feed as either fish oil or linseed oil and can be increased in the blood and milk of ruminants following protection to avoid hydrogenation in the rumen. In western countries the ratio of consumption of n-6 to n-3 PUFAs is greater than 10 and current evidence tends to suggest that a ratio nearer 5 would be more desirable and compatible with cardiovascular well being. As fertility in the UK dairy herd is already poor, it is important to establish whether alterations in dietary n-3 and n-6 PUFAs affects herd fertility before widespread changes in animal diets are recommended. Therefore, this review considers the role played by PUFAs and eicosanoids in fertility, with particular reference to the implications for farm livestock production. The evidence reviewed shows that alteration of the concentration and ratio of n-6 and n-3 PUFAs in feeds can influence prostaglandin synthesis/metabolism in a number of mammalian systems. The changed patterns of prostaglandin synthesis can as a consequence, affect the diverse functions (e.g. hormone secretion) that are normally mediated via prostaglandins. Similarly, changes in prostaglandin synthesis effected through manipulation of PUFAs has a major bearing on fertility (as PGs affect many reproductive parameters, e.g. ovulation). Several studies in cattle and other mammals, show that feeding or infusing different types of fat with varying PUFA content to females can alter: the number and size of ovarian follicles, the ovulation rate, progesterone production by the corpus luteum, the timing of luteolysis and gestational length. In the male most recent work has focussed on sperm production and experiments in fowl have demonstrated clear effects of dietary PUFAs on both the sperm membrane phospholipid composition and on fertilizing ability.

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.

Cellular mechanism of substance P in the regulation of corticosteroid secretion by newt adrenal gland

In this work, we have studied the effects and the possible cellular mechanism of Substance P (SP) on corticosteroid secretion by the adrenal gland of the urodele crested newt, Triturus carnifex. Adrenals were in vitro superfused with SP, prostaglandin E2 (PGE2), nitric oxide (NO) donor, cyclic GMP (cGMP) analogue, and inhibitors of phospholipase A1, phospholipase A2 (PLA2), phospholipase C, adenylate cyclase (AC), cyclooxygenase (COX), NO synthase (NOS), and soluble guanylate cyclase (sGC). PGE2, corticosterone, and aldosterone release and NOS activity were determined. SP, PGE2, NO donor, and cGMP analogue increased corticosterone and aldosterone; SP and PGE2 increased NOS, and SP increased PGE2. PLA2, AC, COX, NOS, and sGC inhibitors counteracted SP and PGE2 effects, except for PLA2, which did not affect PGE2. These results suggest that SP exhibits a stimulatory role on the corticosteroidogenesis of T. carnifex adrenal gland. In particular SP enhances PLA2 activity, increasing PGE2; this prostaglandin affects AC, which, in turn, enhances NO, and the latter therefore affects sGC, with the consequent corticosteroidogenesis increase.

Luteinizing and human chorionic gonadotropin hormones increase intercellular communication and gap junctions in cultured mouse leydig cells

The effect of luteinizing (LH) and human chorionic gonadotropin (hCG) hormones on gap junctions (Gjs) and intercellular communication (ic) was evaluated in Leydig (interstitial) cells from mouse testes. Cell cultures enriched in Leydig cells were studied under control conditions and when maintained in the presence of 100 ng/mL LH, 10 ng/mL hCG, or 1 mM dibutiryl-cAMP (db-cAMP), for 8, 24, and 36 h. To monitor the extent of ic, Lucifer yellow (LY) was injected through a patch pipet into one cell of-small cell aggregates (6-10), and its transfer was evaluated using fluorescent microscopy. The expression of GJs was monitored using immunofluorescent (IF) labeling of connexin 43 (Cx43) with a specific antibody. Testosterone secretion was determined by radioimmunoassay. At all culture times, testosterone levels in the medium were higher in treated than in control cell cultures. In cell cultures of 8 h, LY transferred to most of the neighboring cells (93%) and cell membrane appositions showed abundant Cx43; no difference was found between control and treated cells. In contrast, in control cell cultures of 24 and 36 h, LY transferred to a reduced fraction of neighboring cells (46 and 21%, respectively) and Cx43 labeling was markedly decreased. Addition of LH, hCG, or db-cAMP, to cell cultures for 24 and 36 h completely prevented the decrease in ic and Cx43 expression. Immunoblot studies, from total protein homogenates of cell cultures of 36 h, showed that relative levels of 40- and 43-kDa bands, characteristic of Cx43, were higher in treated than in control cells. These results demonstrate that the expression of Cx43 and ic in Leydig cells is modulated by LH and hCG, and suggest that their effect is mediated by the second messenger of these hormones, cAMP.

Assessment of tissue integrity, ultrastructure and steroidogenic activity of corpora lutea of the marmoset monkey, Callithrix jacchus, following in vitro microdialysis

Microdialysis of marmoset (Callithrix jacchus) corpora lutea in vitro was evaluated regarding morphology, activity of 3 beta-hydroxysteroid-dehydrogenase (3 beta-HSD) and progesterone (P) secretion. Two different dialysis media were used: an unbuffered ringer solution and Krebs-Henseleit buffer gassed with carbogenium. Additionally, the effects of the luteotrophin prostaglandin E2 (PGE2) on P secretion were examined for both media. In general 3 zones of tissue according to the maintenance of cellular integrity could be identified after dialysis. Structurally intact cells were found in close vicinity to the dialysis tubing or the bathing medium after 8 h of perfusion. These 2 zones were separated by a sheet of cells which showed signs of ischemic injury and whose activity of 3-beta-HSD was reduced. During dialysis with ringer solution P release stayed constantly high for a longer period of time than with Krebs buffer. With both media PGE2 stimulated P release but could not prevent the decrease in P production during dialysis with Krebs buffer. In general profiles of baseline secretion, were more stable after treatment than for untreated corpora lutea. There, under dialysis with ringer solution, the ultrastructure of cells close to the dialysis tubing was well preserved exhibiting euchromatic nuclei, tubular sER and numerous mitochondria gathered in the perinuclear region. In contrast, with Krebs buffer heterochromatization of nuclei and vesiculation of smooth endoplasmic reticulum prevailed. After application of PGE2 no histological and ultrastructural differences could be found between tissue dialysed with ringer or Krebs buffer. In these specimens the sER of zone A cells generally appeared vesiculated. Our results indicate (1) a close structure-function relationship of luteal cells in the tested system, (2) the suitability of the system to study intra-luteal regulation and (3) the necessity to control structural integrity of the dialysed tissue.

A novel neuropeptide cellular mechanism in amphibian interrenal steroidogenesis

Interrenals of female Rana esculenta were incubated with gonadotropin-releasing hormone (GnRH), 9-ketoreductase inhibitor (palmitic acid), acetyl salicyclic acid, prostaglandin F2 alpha (PGF2 alpha), forskolin, isobutylmethyl xanthine (IBMX), dibutyril cyclic adenosine monophosphate (dbcAMP). Prostaglandin E2 (PGE2), PGF2 alpha, testosterone and 17 beta-estradiol were assessed on the incubation media. In addition, in the same interrenals, 9-ketoreductase and aromatase activities were evaluated. GnRH increased PGF2 alpha, 17 beta-estradiol, 9-ketoreductase and aromatase, and decreased PGE2 and testosterone. PGF2 alpha increased 17 beta-estradiol and aromatase, and decreased testosterone. Palmitic acid counteracted GnRH effects, while forskolin, IBMX and dbcAMP showed the same PGF2 alpha effects. These results suggest that GnRH stimulates 9-ketoreductase enhancing PGF2 alpha which in turn activates aromatase through cAMP mediation in the interrenal of Rana esculenta.