Hormonal and cellular brain mechanisms regulating the amplexus of male and female water frog (Rana esculenta)

The role of nitric oxide (NO) synthase, prostaglandin E2-9-ketoreductase, and aromatase brain activities in regulating frog amplexus was assessed in the water frog (Rana esculenta). Plasma concentrations of testosterone were higher, and concentrations of 17beta-oestradiol lower, in amplexing males than in unamplexing males; while concentrations of testosterone and PGE2 were lower, and those of 17beta-oestradiol and PGF2alpha higher, in amplexing females compared to unamplexing females. Hormone release rescued from frog brains in vitro mirrored plasma hormone measures. Brain aromatase activity was lower in amplexing males; NO synthase was lower and PGE2-9-ketoreductase and aromatase were higher in amplexing females. In male brains, PGE2-9-ketoreductase inhibitor decreased PGF2alpha release and increased that of PGE2; aromatase inhibitor decreased 17beta-oestradiol and increased testosterone release. In female brains, NO donor and PGE2-9-ketoreductase inhibitor increased testosterone and PGE2 release and decreased that of 17beta-oestradiol and PGF2alpha; NO synthase inhibitor decreased testosterone release and PGE2 and increased 17beta-oestradiol and PGF2alpha release; PGF2alpha decreased testosterone release and increased 17beta-oestradiol release; aromatase inhibitor decreased 17beta-oestradiol release and increased testosterone release. In female brains, NO donor and PGE2-9-ketoreductase inhibitor decreased PGE2-9-ketoreductase and aromatase activities; PGF2alpha increased aromatase activity; NO synthase inhibitor increased PGE2-9-ketoreductase and aromatase activity. The data suggest that, in amplexing female brains, external and/or internal stimuli inhibit NO synthase, decreasing NO and activating PGE2-9-ketoreductase; in turn, PGF2alpha increases aromatase activity and 17beta-oestradiol release; while, in amplexing male brains, stimuli inhibit aromatase activity, thereby increasing testosterone production

Possible roles for prostaglandins E2 and F2 alpha in seasonal changes in ovarian steroidogenesis in the frog (Rana esculenta).

Concentrations of PGE2, PGF2 alpha, androgens and oestradiol in plasma, and ovary weights were measured in the female frog, Rana esculenta, during the annual breeding cycle. Experiments were carried out in vivo to study the effects of PGE2 and PGF2 alpha on plasma sex steroids during the following stages: pre-reproduction (April), reproduction (May), post-reproduction (June) and recovery (October). Experiments were performed in vitro during these stages to evaluate the effects of these two prostaglandins on the secretion of ovarian steroids. Concentrations of PGE2 were low in plasma during winter hibernation, the reproduction and post-reproduction stages, whereas they were high during the pre-reproduction and recovery stages. PGE2 treatment in vivo increased androgen secretion in April, whereas PGF2 alpha treatment increased oestradiol secretion in June and October. In experiments in vitro, PGE2 increased androgen secretion and decreased oestradiol secretion from ovaries collected in April, whereas PGF2 alpha increased oestradiol secretion from ovaries collected in October. These results suggest that a seasonal increase in plasma PGE2 may inhibit breeding activity, probably by stimulating ovarian androgen secretion, whereas, as previously reported, a seasonal increase in plasma PGF2 alpha may inhibit breeding, by stimulating ovarian oestradiol secretion

Nitric oxide synthase acutely regulates progesterone production by in vitro cultured rabbit corpora lutea

We examined the presence and the regulation of nitric oxide (NO) synthase (NOS) using in vitro cultured corpora lutea (CL) obtained from rabbits at days 4 and 9 of pseudopregnancy. The role of NO and NOS on steroidogenesis was also investigated using the same CL preparations after short-term incubations (30 min and 2 h) with the NO donor, sodium nitroprusside (NP), the NOS inhibitor, Nomega-nitro-l-arginine methyl ester (l-NAME) and prostaglandin (PG) F-2alpha. The basal NOS activity was greater in CL at day 4 than at day 9, and was also differently modulated by PGF-2alpha, depending on the age of the CL. The addition of PGF-2alpha to day 4 CL had no effect, but PGF-2alpha on day 9 caused a threefold increase in NOS activity. NP caused a two- to fivefold decrease in release of progesterone from CL of both ages, and this inhibitory effect on steroidogenesis was reversed by l-NAME. All treatments failed to modify basal androgens and 17beta-oestradiol was not detectable in either control or treated CL. These results suggest that NO is effectively involved in the regulation process of steroidogenesis, independently of 17beta-oestradiol. PGF-2alpha had no effect on day 4, but induced luteolysis on day 9, by reducing progesterone (P</=0. 01) to about 18% of control. The luteolytic action of PGF-2alpha was completely reversed by co-incubation with l-NAME, thus supporting the hypothesis that luteolysis is mediated by NO. The addition of NP or l-NAME did not modify the in vitro release of PGF-2alpha. We hypothesised that PGF-2alpha upregulates NOS activity and, consequently, the production of NO, which acutely inhibits progesterone release from day 9 CL of pseudopregnant rabbits

Relationships among GnRH, substance P, prostaglandins, sex steroids and aromatase activity in the brain of the male lizard Podarcis sicula sicula during reproduction.

The release of PGF2 alpha and PGE2, progesterone, androgens and oestradiol in vitro, and the aromatase activity in the brain of the male lizard Podarcis sicula sicula during three different phases of the reproductive period were evaluated. In addition, the effects of salmon GnRH, substance P, salmon GnRH antagonist, substance P antagonist, PGF2 alpha, PGE2 and acetylsalicylic acid on the release of prostaglandins and sex steroids and on aromatase activity in the brain were evaluated during the same three phases. PGF2 alpha, oestradiol and aromatase activity were higher during the refractory phase, androgens during the fighting phase, and progesterone during the mating phase, while PGE2 was lower during the refractory phase. Treatment with salmon GnRH increased PGF2 alpha, oestradiol and aromatase activity, but decreased the amount of androgens released. Substance P decreased PGF2 alpha, oestradiol and aromatase activity, but increased the amount of androgens released. PGF2 alpha increased oestradiol and aromatase activity, but decreased the amount of androgens released. Acetylsalicylic acid decreased PGF2 alpha, oestradiol and aromatase activity, but increased the amount of androgens released. These data suggest that salmon GnRH and substance P have different roles in reproductive processes, with opposite mechanisms, in the central nervous system of this male lizard: salmon GnRH seems to be involved in regulating the refractory phase, while substance P plays a role in regulating the fighting phase

Prostaglandin receptors and role of G protein-activated pathways on corpora lutea of pseudopregnant rabbit in vitro

Studies were conducted to characterize receptors for prostaglandin (PG) F(2alpha) (PGF(2alpha)) and PGE(2), and the signalling pathways regulating total nitric oxide synthase activity and progesterone production in rabbit corpora lutea (CL) of different luteal stages. CL were obtained at days 4, 9 and 13 of pseudopregnancy and cultured in vitro for 2 h with PGF(2alpha) or PGE(2) and with activators and inhibitors of G protein (Gp), phospholipase C (PLC), protein kinase C (PKC), adenylate cyclase (AC) and protein kinase A (PKA). High affinity PGF(2alpha) receptor (K(d)=1.9+/-0.6 nM mean+/-s.e.m. ) concentrations increased (P< or =0.01) four- to five-fold from early to mid- and late-luteal phases (50.6+/-8.5, 188.3+/-36.1 and 231.4+/-38.8 fmol/mg protein respectively). By contrast, PGE(2) receptor (K(d)=1.6+/-0.5 nM) concentrations decreased (P< or =0.01) from day 4 to day 9 and 13 (27.5+/-7.7, 12.4+/-2.4 and 16.5+/-3.0 fmol/mg protein respectively). The Gp-dependent AC/PKA pathway was triggered only on day 4 CL, mimicking the PGE(2) treatment and increasing progesterone production. In both day 9 and day 13 CL, the Gp-activated PLC/PKC pathway evoked a luteolytic effect similar to that induced by PGF(2alpha). The time-dependent selective resistance to PGF(2alpha) and PGE(2) by rabbit CL is mediated by factors other than a lack of luteal receptor-ligand interactions

Bradykinin is not involved in angiotensin converting enzyme modulation of ovarian steroidogenesis and prostaglandin production in frog Rana esculenta

Angiotensin converting enzyme (ACE) was demonstrated to modulate the production of 17beta-estradiol, progesterone and prostaglandin E2 (PGE2) in frog ovary of Rana esculenta. However, the activity was not mediated by angiotensin II (Ang II). In an attempt to identify the peptide involved in the pathway modulated by ACE, bradykinin, another physiological substrate of ACE, was chosen and incubated in the presence of the membrane suspension purified from the frog ovary homogenate. The hydrolytic products were analysed by reverse-phase high-pressure liquid chromatography (HPLC) analysis and the results showed that bradykinin was metabolized by membrane suspension. The presence of the protease inhibitors in the incubation mixture indicated ACE and neutral endopeptidase as being responsible for the bradykinin hydrolysis. Frog ovary was incubated in vitro in the presence of bradykinin (10 microM), bradykinin receptor antagonist NPC 567 (1 mg mL-1), bradykinin fragment (1-7) (10 microM), ACE (2.5 mU mL-1), captopril (0.1 mM) and lisinopril (0.1 mM). The results showed no modulating activity by bradykinin on ovarian 17beta-estradiol and PGE2 production, thus demonstrating that it was not involved in the ACE-modulated pathway

Leptin receptor expression and in vitro leptin actions on prostaglandin release and nitric oxide synthase activity in the rabbit oviduct

In this study, we have examined the presence and the distribution of receptors for leptin (Ob-R) in the oviduct of rabbits, and the effects of leptin on the release of prostaglandin (PG) F2alpha and PGE2 and on the activity of nitric oxide (NO) synthase (NOS) by oviducts cultured in vitro. Rabbits were killed during the follicular phase and the oviducts were incubated in vitro with leptin, PGF2alpha, PGE2, NO donor and inhibitors of NOS and cyclo-oxigenase (COX). Using immunohistochemistry, Ob-R-like positive reaction was observed only in the cytoplasm of secretory cells, having stronger intensity in the infundibulum and ampulla tracts than in the isthmus. Both leptin and NO donor inhibited PGE2 release, whereas they enhanced PGF2alpha release; NOS inhibitor alone or with leptin increased PGE2 and decreased PGF2alpha production; NOS activity was enhanced by leptin, while PGs did not affect this enzyme. This study suggests that the oviduct could be a potential target for endocrine regulation by leptin, whose circulating levels may act as a metabolic signal modulating oviductal PG release through mediation of the NOS/NO system