Gonadotropin-releasing hormone stimulates biosynthesis of prostaglandin F2 alpha by the interrenal gland of the water frog, Rana esculenta, in vitro

Hormonal modulation of phonotaxis and advertisement-call preferences in the gray treefrog (Hyla versicolor)

Hormonal levels fluctuate during the breeding season in many anurans, but the identity of the hormones that modulate breeding behavior and their effects remain unclear. We tested the influence of a combined treatment of progesterone and prostaglandin on phonotaxis, the key proceptive reproductive behavior of female anurans. First, we found that female gray treefrogs (Hyla versicolor) treated with progesterone and prostaglandin exhibited phonotaxis to synthetic male advertisement signals significantly more often than animals treated with ringers vehicle or uninjected controls. Responsive females had greater levels of plasma progesterone and estradiol compared to both control groups, suggesting that these steroids may be promoting phonotaxis. Second, we found that the selectivity of hormonally-induced phonotaxis in H.versicolor was similar to that observed in freshly captured breeding animals. Females made the same choices between acoustic signals after hormone treatments in tests of frequency, call rate and pulse rate, compared to their responses without treatment immediately after collection from the breeding chorus. The preference for a longer call was, however, significantly weaker after hormonal induction of phonotaxis. Hormonally primed females were also less likely to respond in any test and took longer to respond than did freshly collected females. Consequently, our study shows how progesterone-prostaglandin induced phonotaxis in female treefrogs influences both the quality and quantity of phonotaxis, relative to that exhibited by naturally breeding females.

Nitric oxide mediates gonadotropin-releasing hormone effects on frog pituitary

We studied the possible role of nitric oxide (NO) in GnRH-induced gonadotropin secretion in the female water frog, Rana esculenta. During pre-reproduction, pre-ovulation, ovulation, post-ovulation, refractory, recovery and hibernation, pituitaries were incubated with medium-alone, GnRH, NO donor (NOd), NO synthase inhibitor (NOSi), cyclic GMP analogue (cGMPa), soluble guanylate cyclase inhibitor (sGCi), GnRH plus NOSi, GnRH plus sGCi, and NOd plus sGCi. Because antisera raised against gonadotropins are not available for this species, we measured these hormones indirectly through their effects on ovarian progesterone secretion. The ovaries were superfused with the pituitaries pre-incubated as reported above. In addition, NOS activity and cGMP levels were determined in the pre-incubated pituitaries. Those pre-incubated with medium-alone and with GnRH increased progesterone secretion during pre-reproduction, pre-ovulation, ovulation and recovery; the increase induced by GnRH was higher than that induced by medium-alone during pre-reproduction, pre-ovulation and recovery. NOd and cGMPa increased progesterone in all considered reproductive phases except ovulation; the increase induced by NOd and cGMP was higher than that induced by medium-alone during pre-reproduction, pre-ovulation and recovery. NOS activity was highest during ovulation and lowest during post-ovulation, refractory and hibernation. GnRH increased NOS activity during pre-reproduction, pre-ovulation and recovery. Cyclic GMP levels were highest during ovulation and lowest during post-ovulation, refractory and hibernation. GnRH increased cGMP levels during pre-reproduction, pre-ovulation and recovery, NOd during all considered reproductive phases. These results suggest that NO mediates basal and GnRH-induced gonadotropin secretion in female Rana esculenta.

Role of nitric oxide in gonadotropin-releasing hormone-dependent prostaglandin F2 alpha synthesis by frog (Rana esculenta) interrenal gland during post-reproduction

The aim of this study was to clarify the possible involvement of nitric oxide (NO) on prostaglandin (PG) E2-9-ketoreductase activity in the gonadotropin-releasing hormone (GnRH)-dependent PGF2 alpha synthesis by the interrenal gland of the female water frog, Rana esculenta, during the post-reproduction. Interrenal glands were incubated in vitro with GnRH, NO donor (sodium nitroprusside, SNP), and inhibitors of phospholipase C (compound 48/80), inositol triphosphate (decavanadate), calmodulin (calmidazolium), NO synthase (L-NAME), and PGE2-9-ketoreductase (palmitic acid). Production of PGE2 and PGF2 alpha and NO synthase and PGE2-9-ketoreductase activities were determined. GnRH and SNP increased PGF2 alpha production and PGE2-9-ketoreductase activity, and decreased production of PGE2 and GnRH increased NO synthase activity. GnRH effects were blocked by all inhibitors, except for palmitic acid, which did not affect NO synthase activity, which is increased by GnRH. This study indicates that NO may be involved in regulation of the R. esculenta post-reproduction through stimulation of PGE2-9-ketoreductase activity in GnRH-dependent PGF2 alpha synthesis by the frog interrenal gland.

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.

Prostaglandins and corticosterone in the oviparous female lizard, Podarcis sicula sicula, during reproduction

The in vitro effects of prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) on corticosterone release by ovarian follicles, corpora lutea (CL), and interrenals were studied in the female lizard, Podarcis sicula sicula, during reproduction. Follicles and CL studied in the female lizard, Podarcis sicula sicula, during reproduction. Follicles and CL were divided according to their different developmental stages; follicles: previtellogenic, early-vitellogenic, mid-vitellogenic and fully-grown; CL: CL1 (unshelled eggs in the oviducts), CL2 (shelled eggs in the oviducts), CL3 (eggs laid 6 h previously) and CL4 (eggs laid 48 h previously). Interrenals were divided according to the reproductive stages: pre-vitellogenesis, vitellogenesis, ovulation, post-ovulation, and post-deposition. PGF2 alpha release was highest in fully-grown follicles and PGE2 in early-vitellogenic follicles, corticosterone was highest in pre-vitellogenic and lowest in early-vitellogenic follicles. PGE2 decreased corticosterone in pre-vitellogenic, mid-vitellogenic and fully-grown follicles. PGF2 alpha release was highest in CL4, and PGE2 in CL1 and CL2, corticosterone was highest in CL4. PGF2 alpha increased corticosterone in CL1, CL2 and CL3. In interrenals, PGF2 alpha release was highest and PGE2 lowest during ovulation, corticosterone was highest during ovulation. PGF2 alpha increased and PGE2 decreased interrenal corticosterone during vitellogenesis, ovulation, and post-ovulation. In the plasma, PGF2 alpha levels were highest and PGE2 lowest during ovulation, corticosterone was highest during ovulation. These results suggest that corticosterone, modulated by PGF2 alpha and PGE2, is implied in the reproductive processes with different roles. In fact this steroid could favour ovulatory and luteolytic processes. In addition the hypothesis of an anti-vitellogenic role of corticosterone is discussed.

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.

Immunohistochemical localization of GnRH in the crested newt (Triturus carnifex) brain and terminal nerve: a developmental study

Localization of GnRH-immunoreactive neuronal system was studied by immunohistochemistry in the nasal-brain area of the crested newt, Triturus carnifex. Besides adults, developmental stages were those from hatchlings up to complete metamorphosis. Neurons containing immunoreactive GnRH were first detected in the nasal area of larvae with yet undifferentiated gonads. Subsequently, in prometamorphic stages, GnRH-immunoreactive cell bodies and fibers were detected in the proximal part of the terminal nerve as well as along the ventromedial surface of the olfactory bulbs. In older larvae with sexually differentiated gonads and up to the metamorphic climax GnRH-neurons were detected, as a rostral to caudal continuum, along the ventromedial surface of the olfactory bulbs and midtelencephalon. This is exactly the route followed by the terminal nerve. In the adult brain, besides the presence of occasional GnRH-neurons and fibers in the terminal nerve proximal to olfactory bulbs, olfactory bulbs and the mid-basal telencephalon, another aggregate of immunoreactive neurons was present in the anterior preoptic area, and a greater number of fibers in the habenular area as well as in the infundibular floor, median eminence and pars nervosa. These data suggest the nasal area to forebrain migration (along the course of the terminal nerve) of GnRH-neurons during development in the crested newt.

Prostaglandin E2 and prostaglandin F2 alpha involvement in the corticosterone and cortisol release by the female frog, Rana esculenta, during ovulation

Interrenal and ovarian tissues of Rana esculenta were incubated in vitro during the preovulatory, ovulatory and postovulatory phases to study the basal release of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), corticosterone, and cortisol. The effects of exogenous PGE2 and PGF2 alpha on interrenal and ovarian corticosteroid release were also studied. In addition, the plasma values of these four hormones were assessed during the same phases. During in vitro interrenal incubations, PGE2, PGF2 alpha, corticosterone, and cortisol basal releases were higher in the postovulatory phase, PGE2 and PGF2 alpha treatment in vitro increased corticosteroids during the ovulatory phase. During in vitro ovarian incubations, PGE2 basal release was higher in the preovulatory phase and PGF2 alpha and corticosteroids in the ovulatory phase; PGE2 treatment in vitro decreased corticosteroids in the ovulatory phase, and PGF2 alpha increased corticosteroids in the preovulatory and postovulatory phases. PGE2, corticosterone and cortisol plasma values were higher during the postovulatory phase, while PGF2 alpha was elevated during the ovulatory phase. These findings suggest that ovarian corticosteroids could be considered one of the factors inducing ovulation and that their synthesis may be modified by PGs.

Mammalian gonadotropin-releasing hormone increases PGF2 alpha production activating diacylglycerol lipase in Rana esculenta interrenal

The aim of the present paper was to clarify if the prostaglandin F2 alpha (PGF2 alpha) production stimulated by mammalian gonadotropin-releasing hormone (mGnRH) comes from arachidonic acid (AA) freed by diacylglycerol (DAG) and/or membrane phospholipids in the interrenal of Rana esculenta. Interrenals of Rana esculenta were incubated with inhibitors of phospholipase A1 (PLA1), phospholipase A2 (PLA2), phospholipase C (PLC), protein kinase C (PKC) and diacylglycerol lipase (DAGlipase) in the presence or absence of mGnRH. In parallel, the same experiments were carried out using [3H]AA-labelled interrenals. The results of the experiments with non-labelled and [3H]AA-labelled interrenals were in agreement. PLA1, PLA2, PLC, PKC and DAGlipase inhibitors induced a decrease in PGF2 alpha production in interrenals without mGnRH, and PLA2 inhibitor was more effective than other inhibitors. PLC and DAGlipase inhibitors decreased the PGF2 alpha production by interrenals incubated with mGnRH, and PLC inhibitor was more effective than DAGlipase inhibitor. These findings suggest that the main source of AA used for mGnRH-induced PGF2 alpha synthesis is DAG; probably this decapeptide increases PGF2 alpha production enhancing the DAGlipase activity.

In vivo and in vitro studies on effects of beta-endorphin and naloxone on sex steroids in the water frog, Rana esculenta

The effects of beta-endorphin and its receptor antagonist, naloxone, on progesterone, androgens, and oestradiol-17 beta release in male and female Rana esculenta were studied in vivo and in vitro. In the in vivo experiments the frogs underwent hypophysectomy, gonadectomy or both, or were left intact; the animals were injected with beta-endorphin or naloxone and killed after 15, 30, 90 and 240 min. In the in vitro experiments inter-renal, testis and ovary, all with and without added pituitary, were incubated with beta-endorphin or naloxone for 10, 20, 40 and 80 min. The in vivo and in vitro data from males and females were in agreement. In vivo beta-endorphin increased progesterone in all experimental groups and oestradiol in intact and hypophysectomized frogs, while it decreased androgens in all experimental groups. In vitro beta-endorphin increased progesterone in inter-renal and gonadal tissue, and oestradiol in gonads only, while it decreased androgens in inter-renals and gonads. In vivo and in vitro naloxone induced opposite effects to beta-endorphin. These data suggest that in Rana esculenta, opioids are involved in the modulation of hypothalamo-pituitary-inter-renal and gonadal axes. In particular, the data indicate a direct effect of opioids on inter-renal and gonadal sex steroid production.

A possible role of prostaglandin E2 in reproduction of the male water frog, Rana esculenta. In vivo and in vitro studies

Plasma prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), androgens and estradiol-17 beta were measured in the male water frog, Rana esculenta, during the annual sexual cycle. In vivo experiments were carried out to study the effects of PGE2 and PGF2 alpha on plasma sex steroids during the following periods: prereproduction (April), reproduction (May), postreproduction (June) and recovery (October). In the same months, in vitro experiments were performed to evaluate the effects of these two prostaglandins (PGs) on testicular release of sex steroids. The PGE2 plasma levels peaked in April. PGE2 treatment in vivo increased androgens in April and October, while PGF2 alpha increased estradiol-17 beta in June and October. In in vitro experiments, PGE2 increased androgens in April, while PGF2 alpha increased estradiol-17 beta in October. These results suggest that PGE2 could induce the breeding activity, probably through androgens synthesis. PGF2 alpha could interrupt the breeding, through estradiol-17 beta secretion.

Relationships among mammalian gonadotropin-releasing hormone, prostaglandins, and sex steroids in the brain of the crested newt, Triturus carnifex

The present study was carried out to evaluate the in vitro brain release of prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), androgens, and 17 beta-estradiol in male and female crested newt, Triturus carnifex, during three different periods of the annual sexual cycle; in addition, the effects of mammalian gonadotropin-releasing hormone (mGnRH), PGF2 alpha, and PGE2 on prostaglandins and steroids release by the brain were evaluated during the same periods. In brain incubations of both sexes, PGF2 alpha and estradiol were higher during postreproduction, while PGE2 and androgens were higher during reproduction. In both sexes, mGnRH increased PGF2 alpha and estradiol during postreproduction, and PGE2 during reproduction; PGF2 alpha increased estradiol secretion during postreproduction. Only in the male, did both mGnRH and PGE2 increase androgens during reproduction. It could be suggested that in Triturus carnifex, the regulation of the reproductive activity in the central nervous system (CNS) depends on the relationships among mGnRH, prostaglandins and steroids. In particular, PGF2 alpha and PGE2 seem to play different roles in the CNS of the newt: PGF2 alpha is involved in the postreproductive processes, through estradiol secretion, while PGE2 in the reproductive ones (through androgens secretion?).

Mammalian GnRH involvement in prostaglandin F2 alpha and sex steroid hormones testicular release in two amphibian species: the anuran water frog, Rana esculenta, and the urodele crested newt, Triturus carnifex

The present work was carried out to study the in vitro effects of mammalian gonadotropin-releasing hormone (mGnRH) on Rana esculenta and Triturus carnifex testis production of prostaglandin F2 alpha (PGF2 alpha) and sex steroid hormones during the prereproduction, reproduction, and postreproduction periods. In R. esculenta, testicular PGF2 alpha release was lower during postreproduction, and mGnRH increased PGF2 alpha in prereproduction and reproduction. Androgens were higher during prereproduction, and mGnRH induced an androgens increase in prereproduction and reproduction. In T. carnifex testicular PGF2 alpha release was lower during reproduction, and mGnRH increased PGF2 alpha in prereproduction and reproduction. Androgens were higher in reproduction and lower in postreproduction, and mGnRH induced an androgens increase in reproduction. Estradiol-17 beta release was higher in postreproduction, and mGnRH induced an estradiol decrease in reproduction and an increase in postreproduction. These results seem to indicate the involvement of PGF2 alpha in the testicular reproductive activity, and a similar mGnRH mechanism of action, both in R. esculenta and in T. carnifex. In addition, taken together with previous studies, they seem to suggest that the relationship found between mGnRH and PGF2 alpha or sex steroids could be widespread in amphibians.

A possible involvement of prostaglandin F2 alpha (PGF2 alpha) in Rana esculenta ovulation: effects of mammalian gonadotropin-releasing hormone on in vitro PGF2 alpha and 17 beta-estradiol production from ovary and oviduct

The present work studied the PGF2 alpha and 17 beta-estradiol plasma levels during ovulation, and the in vitro effects of mammalian gonadotropin-releasing hormone (mGnRH) on ovarian and oviductal production of prostaglandin F2 alpha (PGF2 alpha) and 17 beta-estradiol during four different stages of the annual sexual cycle in water frog, Rana esculenta. Plasma levels of PGF2 alpha increased in ovulating frogs, with respect to preovulatory and postovulatory levels, while estradiol did not change. In addition, mGnRH increased PGF2 alpha and 17 beta-estradiol in the incubation media of ovaries taken during the recovery stage. Moreover, mGnRH increased PGF2 alpha in incubation media of oviducts collected during the reproductive stage. These findings suggest that PGF2 alpha could be involved in the control of egg deposition in the female R.

In vivo and in vitro studies on the effects of mGnRH on oestradiol-17 beta inter-renal production in the female frog, Rana esculenta, during the post-reproductive period

Plasma oestradiol-17 beta was measured by RIA, in female, Rana esculenta, submitted to hypophysectomy, gonadectomy, or both, and treated with mammalian gonadotropin-releasing hormone (mGnRH), homologous pituitary homogenate, or both, during the post-reproductive period. In addition, the oestradiol-17 beta release was measured in in vitro incubations of ovaries or interrenals treated with mGnRH, pituitary, or both, during the same period. In vivo and in vitro mGnRH and/or pituitary directly stimulated the production of oestradiol-17 beta by the interrenal, but not by ovary, although the stimulatory effects of the pituitary are minor and delayed with respect to those of mGnRH. These results seem to indicate that mGnRH and pituitary, with probably different mechanisms, stimulate the interrenal to produce high levels of oestradiol which is involved in the post-reproductive refractoriness.

PGF2 alpha, PGE2, and sex steroids from the abdominal gland of the male crested newt Triturus carnifex (Laur.)

Prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), progesterone, androgens, and 17 beta-estradiol in vitro release by the abdominal gland of the crested newt, Triturus carnifex (Laur.), was studied during the prereproductive, reproductive and postreproductive periods. In addition, the in vitro effects of the PGF2 alpha and/or PGE2 on progesterone, androgens and estradiol release by the abdominal gland were evaluated. PGF2 alpha, PGE2 and progesterone release was higher during the reproductive period, and in the same period, PGE2 treatment induced a progesterone increase. PGF2 alpha induced an increase of abdominal gland estradiol release at the end of the reproductive period. These results seemed to confirm the pheromonal role assigned to progesterone, and suggested a PGE2 stimulatory role in inducing progesterone release, even if pheromonal activity of PGF2 alpha and PGE2 cannot be excluded. In addition, PGF2 alpha-dependent estradiol increase at the end of reproduction could be interpreted as a mechanism for interruption of the abdominal gland activity.

Plasma prostaglandin F2 alpha and reproduction in the female Triturus carnifex (Laur.)

Plasma patterns of prostaglandin F2 alpha (PGF2 alpha) and sex hormones (progesterone, androgens and 17 beta-estradiol) have been studied in the female crested newt, Triturus carnifex (Laur.), during the annual sexual cycle. The effects of exogenous PGF2 alpha on sex hormones were determined. In addition, the effects of one week's captivity on plasma PGF2 alpha and sex hormones were reported. PGF2 alpha plasma level peaked in April, was low in summer, and progressively increased during the autumn to peak again in December. The April PGF2 alpha coincided with a 17 beta-estradiol rise, and with a progesterone drop. The autumn PGF2 alpha increase was coupled to a 17 beta-estradiol rise, and therefore it has been tentatively related to ovary and oviduct development. In newts collected in April, moreover, a PGF2 alpha-dependent 17 beta-estradiol synthesis could occur, since PGF2 alpha injection induced a significant 17 beta-estradiol plasma increase. These findings led us to suppose that PGF2 alpha intervenes in spring breeding season termination through the induction of a 17 beta-estradiol synthesis as in other amphibian species. PGF2 alpha injection caused a progesterone decrease, probably by inducing corpora lutea lysis. The patterns of plasma sex hormones were consistent with the results reported for the same newt species.