Seasonal testosterone profile and testicular responsiveness to pituitary factors and gonadotrophin releasing hormone during two different phases of the sexual cycle of the frog (Rana esculenta)

Celebrating 50+ years of research on the reproductive biology and endocrinology of the green frog: An overview

This issue is dedicated to the late Professor Giovanni Chieffi, and this article is an overview of the research on Comparative Endocrinology of reproduction using Rana esculenta (alias Pelophylax esculentus) as a model system. Starting from the early 1970s till today, a large quantity of work have been conducted both in the fields of experimental endocrinology and in the definition of the diffuse neuroendocrine system, with a major focus on the increasing role of regulatory peptides. The various aspects investigated concerned the histological descriptions of principal endocrine glands of the hypothalamic-pituitary-gonadal (HPG) axis, the localization and distribution in the HPG of several different substances (i.e. neurosteroids, hypothalamic peptide hormones, pituitary gonadotropins, gonadal sex steroids, and other molecules), the determination of sex hormone concentrations in both serum and tissues, the hormone manipulations, as well as the gene and protein expression of steroidogenic enzymes and their respective receptors. All together these researches, often conducted considering different periods of the annual reproductive cycle of the green frog, allowed to understand the mechanism of cascade control/regulation of the HPG axis of R. esculenta, characterizing the role of different hormones in the two sexes, and testing the hypotheses about the function of single hormones in different target organs. It becomes evident from the review that, in their simplest form, several features of this species are specular as compared to those of other vertebrate species and that reproduction in this frog species is either under endogenous multi-hormonal control or by a wide array of different factors. Our excursus of this research, spanning almost five decades, shows that R. esculenta has been intensively and successfully used as an animal model in reproductive endocrinology as well as several field studies such as those involving environmental concerns that focus on the effects of endocrine disruptors and other environmental contaminants.

The Cannabinoid Receptor CB1 Stabilizes Sperm Chromatin Condensation Status During Epididymal Transit by Promoting Disulphide Bond Formation

The cannabinoid receptor CB1 regulates differentiation of spermatids. We recently characterized spermatozoa from caput epididymis of CB1-knock-out mice and identified a considerable number of sperm cells with chromatin abnormality such as elevated histone content and poorly condensed chromatin. In this paper, we extended our findings and studied the role of CB1 in the epididymal phase of chromatin condensation of spermatozoa by analysis of spermatozoa from caput and cauda epididymis of wild-type and CB1-knock-out mouse in both a homozygous or heterozygous condition. Furthermore, we studied the impact of CB1-gene deletion on histone displacement mechanism by taking into account the hyperacetylation of histone H4 and players of displacement such as Chromodomain Y Like protein (CDYL) and Bromodomain testis-specific protein (BRDT). Our results show that CB1, via local and/or endocrine cell-to-cell signaling, modulates chromatin remodeling mechanisms that orchestrate a nuclear condensation extent of mature spermatozoa. We show that CB1-gene deletion affects the epididymal phase of chromatin condensation by interfering with inter-/intra-protamine disulphide bridges formation, and deranges the efficiency of histone removal by reducing the hyper-acetylation of histone H4. This effect is independent by gene expression of Cdyl and Brdt mRNA. Our results reveal a novel and important role for CB1 in sperm chromatin condensation mechanisms.

Anandamide acts via kisspeptin in the regulation of testicular activity of the frog, Pelophylax esculentus

In the frog Pelophylax esculentus, the endocannabinoid anandamide (AEA) modulates Gonadotropin Releasing Hormone (GnRH) system in vitro and down-regulates steroidogenic enzymes in vivo. Thus, male frogs were injected with AEA ± SR141716A, a cannabinoid receptor 1 (CB1) antagonist, to evaluate possible effects on GnRH and Kiss1/Gpr54 systems, gonadotropin receptors and steroid levels. In frog diencephalons, AEA negatively affected both GnRH and Kiss1/Gpr54 systems. In testis, AEA induced the expression of gonadotropin receptors, cb1, gnrh2 and gnrhr3 meanwhile reducing gnrhr2 mRNA and Kiss1/Gpr54 proteins. Furthermore, aromatase (Cyp19) expression increased in parallel to testosterone decrease and estradiol increase. In vitro treatment of testis with AEA revealed direct effects on Cyp19 and induced the expression of the AEA-degrading enzyme Faah. Lastly, AEA effects on Faah were counteracted by the antiestrogen ICI182780, indicating estradiol mediated effect. In conclusion, for the first time we show in a vertebrate that AEA regulates testicular activity through kisspeptin system.

Seminiferous Epithelium Cycle in Bombina orientalis

The purpose of the present study was to examine the seminiferous epithelium cycle of Bombina orientalis using a light microscope. The cycle was divided into a total of 10 stages, according to the morphological characteristics of the cells. The spermatogenetic cells included primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatid and sperm. At stage I, the primary spermatogonia was located closer to basal lamina of the seminiferous tubule without spermatocyst formations. Especially at the stage II, the secondary spermatogonia were located in the spermatocyst. The primary and secondary spermatocytes were found from stages III to VI. The secondary spermatocytes were smaller in size than the primary spermatocytes, but they had thicker nucleoplasm and smaller nuclei. The round-shaped, early sperm cells were formed in stage VII, and further divided at stage VIII to have more concentrated nucleoplasm before division to matured sperm cells. At stage X, the matured sperm cells emerged from the spermatocyst. Considering the above results, this study presented the special characteristics in the generation and type of sperm formation. The germ cell formation occurred in various stages, like the perspectives of Franca et al (1999), ultimately, providing taxonomically useful information.

Seminiferous Epithelium Cycle in Bombina orientalis

The purpose of the present study was to examine the seminiferous epithelium cycle of Bombina orientalis using a light microscope. The cycle was divided into a total of 10 stages, according to the morphological characteristics of the cells. The spermatogenetic cells included primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatid and sperm. At stage I, the primary spermatogonia was located closer to basal lamina of the seminiferous tubule without spermatocyst formations. Especially at the stage II, the secondary spermatogonia were located in the spermatocyst. The primary and secondary spermatocytes were found from stages III to VI. The secondary spermatocytes were smaller in size than the primary spermatocytes, but they had thicker nucleoplasm and smaller nuclei. The round-shaped, early sperm cells were formed in stage VII, and further divided at stage VIII to have more concentrated nucleoplasm before division to matured sperm cells. At stage X, the matured sperm cells emerged from the spermatocyst. Considering the above results, this study presented the special characteristics in the generation and type of sperm formation. The germ cell formation occurred in various stages, like the perspectives of Franca et al (1999), ultimately, providing taxonomically useful information.

Kisspeptin drives germ cell progression in the anuran amphibian Pelophylax esculentus: a study carried out in ex vivo testes

Kisspeptin, via Gpr54 receptor, regulates puberty onset in most vertebrates. Thus, the direct involvement of kisspeptin activity in testis physiology was investigated in the anuran amphibian, Pelophylax esculentus. In this vertebrate gpr54 mRNA has been localized in both interstitial compartment and spermatogonia (SPG), whereas SPG proliferation requires the cooperation between estradiol and testicular Gonadotropin releasing hormone (Gnrh). In the pre-reproductive period, dose response curve to assess the effects of Kisspeptin-10 (Kp-10) was carried out in vitro (dose range: 10(-9)-10(-6)M; incubation times: 1 and 4h); proliferative activity and germ cell progression were evaluated by expression analysis of proliferating cell nuclear antigen (pcna), estrogen receptor beta (erβ), Gnrh system (gnrh1, gnrh2, gnrhr1, r2, r3) and by the count of empty, mitotic and meiotic tubules. All selected markers were up regulated at 4h Kp-10 incubation. Histological analysis also proved the increase of mitotic activity and the progression of spermatogenesis. Besides Kp-10 modulation of testicular Gnrh system, in vitro treatment with 17β-estradiol (10(-6)M) ± the antagonist ICI182-780 (10(-5)M) revealed gnrh2 and gnrhr3 estrogen dependent expression. In the reproductive period, testes were incubated for 1 and 4h with Kp-10 (10(-7)M) or Kp-10 (10(-7)M)+kisspeptin antagonist [Kp-234 (10(-6)M)]. Results obtained in the pre-reproductive period were confirmed and Kp-234 completely counteracted Kp-10 effects. In conclusion, Kp-10 modulated the expression of pcna, erβ, gnrhs and gnrhrs, inducing the progression of the spermatogenesis.

Immunoexpression of aromatase and estrogen receptors β in stem spermatogonia of bullfrogs indicates a role of estrogen in the seasonal spermatogonial mitotic activity

Bullfrog stem spermatogonia, also named primordial germ cells (PGCs), show strong testosterone immunolabeling in winter, but no or weak testosterone immunoexpression in summer. Thus, the role of testosterone in these cells needs to be clarified. In this study, we proposed to evaluate whether PGCs express aromatase and estrogen receptors, and verify a possible role of estrogen in PGCs seasonal proliferation. Testes of male adult bullfrogs, collected in winter (WG) and summer (SG), were fixed and embedded in historesin, for quantitative analysis, or paraffin for immunohistochemistry (IHC). The number of haematoxylin/eosin stained PGCs/lobular area was obtained. Proliferating cell nuclear antigen (PCNA), aromatase, estrogen receptor β (ERβ) and PCNA/ERβ double immunolabeling were detected by IHC. The number of PCNA-positive PGCs and the histological score (HSCORE) of aromatase and ERβ immunolabeled PGCs were obtained. Although the number of PGCs increased significantly in WG, a high number of PCNA-positive PGCs was observed in summer. Moreover, aromatase and ERβ HSCORE was higher in SG than WG. The results indicate that PGCs express a seasonal proliferative activity; the low mitotic activity in winter is related to the maximal limit of germ cells which can be supported in the large lobules. In SG, the increased ERβ and aromatase HSCORE suggests that testosterone is converted into estrogen from winter to summer. Moreover, the parallelism between the high PGCs mitotic activity and ERβ immunoexpression suggest a participation of estrogen in the control of the PGCs seasonal proliferative activity which guarantee the formation of new germ cysts from summer to next autumn.

Primordial germ cells (spermatogonial stem cells) of bullfrogs express sex hormone-binding globulin and steroid receptors during seasonal spermatogenesis

In vertebrate species, testosterone seems to inhibit spermatogonial differentiation and proliferation. However, this androgen can also be converted, via aromatase, into estrogen which stimulates spermatogonial differentiation and mitotic activity. During seasonal spermatogenesis of adult bullfrogs Lithobates catesbeianus, primordial germ cells (PGCs) show enhanced testosterone cytoplasm immunoexpression in winter; however, in summer, weak or no testosterone immunolabelling was observed. The aim of this study was to confirm if PGCs express stem cell markers - alkaline phosphatase (AP) activity and GFRα1 (glial-cell-line-derived neurotrophic factor) - and verify whether testosterone is maintained in these cells by androgen receptors (ARs) and/or sex hormone-binding globulin (SHBG) in winter. Furthermore, regarding the possibility that testosterone is converted into estrogen by PGCs in summer, the immunoexpression of estrogen receptor (ER)β was investigated. Bullfrog testes were collected in winter and in summer and were embedded in glycol methacrylate for morphological analyses or in paraffin for the histochemical detection of AP activity. GFRα1, AR, SHBG and ERβ expression were detected by Western blot and immunohistochemical analyses. The expression of AP activity and GFRα1 in the PGCs suggest that these cells are spermatogonial stem cells. In winter, the cytoplasmic immunoexpression of ARs and SHBG in the PGCs indicates that testosterone is maintained by these proteins in these cells. The cytoplasmic immunoexpression of ERβ, in summer, also points to an ER-mediated action of estrogen in PGCs. The results indicate a participation of testosterone and estrogen in the control of the primordial spermatogonia during the seasonal spermatogenesis of L. catesbeianus.

Anandamide regulates the expression of GnRH1, GnRH2, and GnRH-Rs in frog testis

Gonadotropin-releasing hormone (either GnRH1 or GnRH2) exerts a local activity in vertebrate testis, including human testis. Relationships between endocannabinoid (eCB) and GnRH systems in gonads have never been elucidated in any species so far. To reveal a cross-talk between eCBs and GnRH at testicular level, we characterized the expression of GnRH (GnRH1 and GnRH2) as well as GnRH receptor (GnRH-R1, -R2, and -R3) mRNA in the testis of the anuran amphibian Rana esculenta during the annual sexual cycle; furthermore, the corresponding transcripts were localized inside the testis by in situ hybridization. The possible endogenous production of the eCB, anandamide (AEA), was investigated in testis by analyzing the expression of its biosynthetic enzyme, Nape-pld. Incubations of testis pieces with AEA were carried out in the postreproductive period (June) and in February, when a new spermatogenetic wave takes place. In June, AEA treatment significantly decreased GnRH1 and GnRH-R2 mRNA, stimulated the transcription of GnRH2 and GnRH-R1, and did not affect GnRH-R3 expression. In February, AEA treatment upregulated GnRH2 and GnRH-R3 mRNA, downregulated GnRH-R2, and did not affect GnRH1 and GnRH-R1 expression. These effects were mediated by type 1 cannabinoid receptor (CB1) since they were fully counteracted by SR141716A (Rimonabant), a selective CB1 antagonist. In conclusion, eCB system modulates GnRH activity in frog testis during the annual sexual cycle in a stage-dependent fashion.

The contribution of lower vertebrate animal models in human reproduction research

Many advances have been carried out on the estrogens, GnRH and endocannabinoid system that have impact in the reproductive field. Indeed, estrogens, the generally accepted female hormones, have performed an unsuspected role in male sexual functions thanks to studies on non-mammalian vertebrates. Similarly, these animal models have provided important contributions to the identification of several GnRH ligand and receptor variants and their possible involvement in sexual behavior and gonadal function regulation. Moreover, the use of non-mammalian animal models has contributed to a better comprehension about the endocannabinoid system action in several mammalian reproductive events. We wish to highlight here how non-mammalian vertebrate animal model research contributes to advancements with implications on human health as well as providing a phylogenetic perspective on the evolution of reproductive systems in vertebrates.

Cannabinoids and Reproduction: A Lasting and Intriguing History

Starting from an historical overview of lasting Cannabis use over the centuries, we will focus on a description of the cannabinergic system, with a comprehensive analysis of chemical and pharmacological properties of endogenous and synthetic cannabimimetic analogues. The metabolic pathways and the signal transduction mechanisms, activated by cannabinoid receptors stimulation, will also be discussed. In particular, we will point out the action of cannabinoids and endocannabinoids on the different neuronal networks involved in reproductive axis, and locally, on male and female reproductive tracts, by emphasizing the pivotal role played by this system in the control of fertility.

Testicular gonadotropin-releasing hormone activity, progression of spermatogenesis, and sperm transport in vertebrates

Since the end of the 1970s, studies have shown that, besides the endocrine route, a chemical mediator may also act through autocrine and/or paracrine mechanisms. This has opened new frontiers for research as a result of a redefinition of what endocrinology represents. Apart from androgens within the male gonad, testicular gonadotropin-releasing hormone, estrogens, molecular chaperones, proto-oncogenes, and, very recently, the endocannabinoid system have been shown to play important roles. Their activities to regulate spermatogenesis, including spermiogenesis and sperm maturation, will be discussed from the comparative viewpoint to describe adaptive phenomena and to speculate on evolution.

The effects of oestrogen receptors α and β on testicular cell number and steroidogenesis in mice

Oestrogen plays an important role in testicular function. This study used mice null for oestrogen receptor α (ERα) or β (ERβ) to investigate which receptor mediates the effects of oestrogen within the testis. Groups of ERα knockout mice (αERKO) and ERβ knockout mice (βERKO) and wild-type littermates (n=5–8) were killed at 11 weeks post partum. One testis was fixed in Bouin’s fluid for stereology and the other frozen for testosterone measurement. Trunk blood was collected for testosterone RIA. The optical disector combined with the fractionator methodology was used to estimate Leydig, Sertoli and germ cell numbers. At all times, the knockout animals were compared with their wild-type littermates. The physical disector quantified cells stained immunohistochemically for the apoptotic marker active caspase-3 and Hoechst staining was used to identify nuclear fragmentation. The mean Leydig cell volume was measured using the point sampled intercept method. The Leydig cell number per testis was significantly increased in βERKO mice but not in αERKO mice. Plasma and testicular testosterone concentrations were increased in αERKO mice but no changes were observed in βERKO mice. Hypertrophic Leydig cell changes were observed in αERKO mice, and a decreased mean cell volume was seen in βERKO mice. No difference in Sertoli cell number per testis was observed in any of the groups. The spermatogonial cell number per testis was increased in βERKO mice. Immunohistochemistry identified increased numbers of active caspase-3-labelled germ cells per testis in αERKO mice but not βERKO mice. Hoechst staining supported these findings. There was significant germ cell loss in αERKO mice. This study suggests that ERβ may be involved in regulation of Leydig cell proliferation and testosterone production in the adult mouse testis.

Synthetic seminal plasma peptide inhibits testosterone production in frog testis in vitro

The role of synthetic seminal plasma peptide, designed using biochemical and mass spectroscopy analyses of native peptides extracted from seminal plasma, was studied in amphibian (Rana esculenta) testicular steroidogenesis. Production of testosterone and prostaglandin F(2alpha) was determined by incubating frog testes with synthetic peptide in vitro. Analysis of the data showed a dose-dependent inhibition of testosterone production (43% at 10(-5) M concentration) without prostaglandin F(2alpha) synthesis being affected. Determination of the peptide activity during the annual R. esculenta reproductive cycle showed inhibition of testosterone production in post-reproductive and recovery periods, suggesting a possible involvement of peptide in gonad steroidogenesis.

The expression level of frog relaxin mRNA (fRLX), in the testis of Rana esculenta, is influenced by testosterone

Frog relaxin (fRLX) belongs to the relaxin/insulin gene family present in the testis of Rana esculenta and is specifically expressed by Leydig cells. Since the expression of fRLX transcript changes during the reproductive cycle and is more abundant when circulating levels of androgens are relatively high, we investigated the effect(s) of testosterone and its antagonist (cyproterone acetate, CPA) on its expression pattern, in the testis of the frog Rana esculenta. Results from in vivoand in vitro experiments demonstrate that testosterone strongly induces a significant increase of fRLX mRNA expression in frog testes and, this effect is counteracted by CPA, supporting the existence of intratesticular (autocrine/paracrine) mechanisms of action. Interestingly, in both the control and testosterone-treated testes, fRLX mRNA expression was markedly decreased 24 h post-treatment, as compared to that measured at 2 h and 8 h post-treatment, suggesting that factor(s), other than testosterone, may act(s) in controlling its expression. In addition, RT-PCR analysis and in situ hybridization performed on frog testis injected with CPA for 15 days, on alternate days, showed a strong decrease of fRLX expression, suggesting that CPA counteracts the effect of testosterone on fRLX expression. Taken together our results strongly indicate that changes in the production, by the Leydig cells, of both testosterone and fRLX may represent a marker for the study of Leydig cell activity in the testis of the frog Rana esculenta.

Testosterone-immunopositive primordial germ cells in the testis of the bullfrog, Rana catesbeiana

In amphibia, steroidogenesis remains quiescent in distinct seasonal periods, but the mechanism by which spermatogenesis is maintained under low steroidogenic conditions is not clear. In the present study, testosterone location in the testes of Rana catesbeiana was investigated immunohistochemically during breeding (summer) and nonbreeding (winter) periods. In winter, the scarce interstitial tissue exhibited occasional testosterone immunopositivity in the interstitial cells but the cytoplasm of primordial germ cells (PG cells) was clearly immunopositive. By contrast, in summer, PG cells contained little or no immunoreactivity whereas strong immunolabelling was present in the well-developed interstitial tissue. These results suggest that PG cells could retain testosterone during winter. This androgen reservoir could be involved in the control of early spermatogenesis in winter and/or to guarantee spermiogenesis and spermiation in the next spring/summer. The weak or negative immunoreaction in the summer PG cells might reflect consumption of androgen reservoir by the intense spermatogenic activity from spring to summer. Thus, besides acting as stem cells, PG cells of R. catesbeiana could exert an androgen regulatory role during seasonal spermatogenesis.

Testosterone secretion and pharmacological spermatozoal recovery in the cane toad (Bufo marinus)

The cane toad (Bufo marinus) was used as a model to study male anuran reproductive endocrinology and to develop a protocol for non-invasive sperm recovery. Circulating testosterone concentrations in 6-hourly samples did not vary significantly (P < 0.05) over a 24 h period although there was a tendency (P = 0.06) for testosterone to be elevated at 19:00 h relative to other times of the day, which may be related to the nocturnal activity pattern of this species. Testosterone secretion after intraperitoneal (IP) injection of either a GnRH agonist (5 microg IP) or hCG (1000 IU) was also examined. While the GnRH agonist did not produce a significant increase above basal plasma testosterone (0.29, 95% C.I. of 0.05-1.10 ng/ml), injection of hCG resulted in an increase (P < 0.01) of plasma testosterone with peak concentrations at approximately 120 min (4.17, 95% C.I. of 2.69-7.44 ng/ml) after injection. Non-invasive pharmaceutical sperm recovery was attempted following IP injection of graded doses of GnRH agonist, hCG or FSH. Urine was collected at 3, 6 and 12 h after treatment to assess sperm quality and quantity. The optimal protocol for sperm recovery in cane toads was injection of either 1000 or 2000 IU hCG; there was no significant difference in the quality of the spermic urine samples obtained using either dose of hCG or with respect to collection time. The findings indicated that hCG can be used to assess testicular steroidogenic status and also to induce sperm recovery in the cane toad. The hCG protocols developed in this study will have application in studies on the reproductive biology of rare and endangered male anurans.

Effect of bullfrog LH and FSH on newt testes under different temperatures

Environmental temperature plays important roles for amphibian gonadal function. In this study, we examined the responses of testicular tissue of adult male newts (Cynops pyrrhogaster) to amphibian gonadotropins both in vitro and in vivo under different temperatures. When minced testes were incubated in vitro at different temperatures (8-37 degrees C) under an atmosphere of 95% O(2)-5% CO(2) for 3h with bullfrog luteinizing hormone (LH) or follicle-stimulating hormone (FSH), LH stimulated testosterone production more than FSH. The testosterone production increased as the incubation temperature increased. Hypophysectomized newts were injected with bullfrog LH or FSH and maintained at 8 or 18 degrees C. In the 18 degrees C group, the testicular weight of the hypophysectomized control decreased when compared with that of with the intact control. The testicular weight of the LH-treated hypophysectomized group decreased more than that of the hypophysectomized control, indicating that LH induced the evacuation of mature spermatozoa from the testes of LH-treated hypophysectomized newts. In the FSH-treated newts, the testicular weight was greater than that in the hypophysectomized control, and was maintained at a value similar to that of the intact control. In the 8 degrees C group, there was no significant difference in testicular size among the intact control, hypophysectomized control, and FSH-treated newts. LH strongly induced spermiation as it did at 18 degrees C. The plasma testosterone level in the hypophysectomized newts decreased dramatically, but LH was effective in restoring it. Its effect was more potent at 8 degrees C than at 18 degrees C. On the other hand, FSH did not induce a significant increase in the plasma testosterone levels at either temperatures. The results indicate a temperature-dependent difference in responsiveness of the testis both in vitro and in vivo to LH and FSH.

Testicular morphological changes during the seasonal reproductive cycle in the bullfrog Rana catesbeiana

Spermatogenesis and steroidogenesis undergo seasonal variations during the reproductive cycle in amphibians. Testicular morphological and morphometric seasonal variations as well as interstitial lipidic inclusions and intralobular glycoconjugates were evaluated during seasonal cycle of Rana catesbeiana. Testes of frogs collected during the annual seasons were weighed for calculation of GSI (Gonadosomatic index). Seminiferous lobule diameters (DSL) and volume densities of seminiferous lobules (VvSL), excretory ducts (VvED), and interstitial tissue (VvIT) were analyzed. Semithin sections were submitted to Periodic Acid-Schiff (PAS) and Alcian Blue (AB) methods for detection of glycoconjugates, while lipidic inclusions were detected by Sudan Black B. GSI showed no significant variations during the year. Since VvED and VvIT increased significantly during summer and were inversely proportional to VvSL, a compensatory effect between the testicular compartments may be related to the maintenance of GSI. During autumn/winter, larger lobular diameters were observed in comparison to spring/summer when spermiogenesis and spermiation were commonly observed. The increased VvIT and the numerous lipidic inclusions in the interstitial cells during summer suggest a relationship between spermiogenesis and steroidogenesis. Besides the structural stability variations occurring in the IT and SL, a possible paracrine interaction between ED and IT should be also involved in the IT development during summer. The presence of PAS and AB-positive globular structures were observed in the seminiferous lobules and excretory ducts. These structures containing acid glycoconjugates appear to be Sertoli cell apical portions, which are accumulated in the lumen of the seminiferous lobules mainly during spermiation.

Spermatogenesis and plasma testosterone levels in Western Australian burrowing desert frogs, Cyclorana platycephala, Cyclorana maini, and Neobatrachus sutor, during aestivation

Changes in testis size, histological status, and plasma levels of testosterone were monitored for males of three species of Western Australian desert frogs, Cyclorana maini, Cyclorana platycephala, and Neobatrachus sutor during aestivation. The frogs were induced to burrow and form cocoons soon after their capture and then disinterred at intervals in order to monitor changes in reproductive activity of the testes. All stages of spermatogenesis were evident in active frogs, which were collected a few days following rain from breeding choruses. Relative testis mass declined gradually in all species during the first 7 months of aestivation and then increased significantly at 16-19 months in the two species for which extended data were available (C. maini and N. sutor). A decrease in the number of sperm bundles 2-4 months after cocooning was associated with an initial increase in the number of free spermatazoa in all three species, which then returned to the levels seen in active animals after 7 months. Increases in the number of primary and secondary spermatogonia were most evident in C. platycephala after 4-7 months of aestivation, but early stages of spermatocytogenesis were evident in all species after 7 months of aestivation, especially in individuals that contained neither sperm bundles nor mature spermatazoa. Changes in plasma testosterone levels correlated significantly with variations in the diameter of the seminiferous tubules and the GSI, suggesting that this hormone plays a major role in controlling testicular recrudescence in aestivating, cocooned, desert frogs. Data from this study show that, in the absence of any external cues, testicular recrudescence is evident after approximately one year of aestivation in desert frogs which prepares them to breed again, once rain falls.

Evolutionary aspects of cellular communication in the vertebrate hypothalamo-hypophysio-gonadal axis

This review emphasizes the comparative approach for developing insight into knowledge related to cellular communications occurring in the hypothalamus-pituitary-gonadal axis. Indeed, research on adaptive phenomena leads to evolutionary tracks. Thus, going through recent results, we suggest that pheromonal communication precedes local communication which, in turn, precedes communication via the blood stream. Furthermore, the use of different routes of communication by a certain mediator leads to a conceptual change related to what hormones are. Nevertheless, endocrine communication should leave out of consideration the source (glandular or not) of mediator. Finally, we point out that the use of lower vertebrate animal models is fundamental to understanding general physiological mechanisms. In fact, different anatomical organization permits access to tissues not readily approachable in mammals.

Cytoplasmic versus nuclear localization of Fos-related proteins in the frog, Rana esculenta, testis: in vivo and direct in vitro effect of a gonadotropin-releasing hormone agonist

Evidence has been accumulated indicating that GnRH-like peptides are present in a variety of extrabrain areas of mammalian and nonmammalian vertebrates. A pioneer study carried out in the frog, Rana esculenta, demonstrated that testicular GnRH induced spermatogonial proliferation. Recently, we have shown that in proliferating spermatogonia (SPG) of frogs, a change of localization of the oncoprotein Fos, from the cytoplasm to the nucleus, occurs. This leads to the hypothesis that one or more testicular GnRH peptides may regulate SPG proliferation through Fos family proteins. Therefore, in vivo experiments in intact R. esculenta and in vitro incubations of testis fragments have been carried out using GnRH agonist (GnRHa; buserelin) and GnRH antagonist (D-pGlu(1),D-Phe(2),D-Trp(3,6)-GnRH). Cytoplasmic and nuclear Fos-like protein localization has been found by Western blot analysis in testicular extracts. Immunocytochemistry confirmed that cytoplasmic immunostaining was restricted to SPG; change of localization into the nuclear compartment was observed after GnRHa treatment. Northern blot analysis showed that treatments of testis fragments with GnRHa did not modify testicular c-fos mRNA expression. On the contrary, a Fos-like protein of 52 kDa, while not affected in vivo, disappeared from testicular cytosolic extracts after in vitro treatment with GnRHa. Contemporaneously, a 55-kDa Fos-related signal appeared in nuclear extracts. The GnRH antagonist counteracted the effects of GnRHa. Furthermore, in vivo treatments showed that GnRHa acted negatively on a 43-kDa nuclear Fos-related signal and that gonadotropins caused the decrease of 52-kDa cytoplasmic signal. In conclusion, we show, to our knowledge for the first time, that Fos is regulated by GnRHa directly (not through the pituitary) at the testicular level. The main effect appears to be related to Fos translocation from cytoplasmic to nuclear compartments of SPG.

Stage-dependent and alternative splicing of sGnRH messengers in rainbow trout testis during spermatogenesis

The gonadotropin releasing hormone (GnRH) has long been considered as a neuropeptide involved in the control of the reproductive cycle. However, the presence of GnRH and its receptors in various tissues, including ovary and testis, suggests a role as autocrine/paracrine factor. In the present study, we report the expression of the sGnRH-1 and sGnRH-2 genes encoding salmon GnRH in rainbow trout testis throughout testicular development and spermatogenesis. We demonstrate that both sGnRH mRNA are expressed prior of sexual differentiation. In adult, northern blot analysis indicates that sGnRH-2 transcripts are expressed in the testis at higher levels than sGnRH-1 messengers. Moreover, we observed that the expression of sGnRH-2, and not sGnRH-1, messengers was stage-dependent. sGnRH-2 mRNA expression decreases at the onset and progressively rebounds at the end of spermatogenesis. In addition, we demonstrate that a complex stage-dependent and differential splicing of the sGnRH-2 messengers occurs throughout spermatogenesis. We isolated five transcripts corresponding to sGnRH-2 messengers. Two of them may encode a novel and shortened GnRH-associated peptide containing 18 residues instead of 46. Our data provide new insight in the putative role of GnRH and GAP peptides as autocrine/paracrine factors of spermatogenesis.

Seasonal changes of testicular weight, sperm production, serum testosterone, and in vitro testosterone release in Korean ring-necked pheasants (Phasianus colchicus karpowi)

To study the biology of reproduction of male Korean ring-necked pheasants kept under natural conditions of temperature and photoperiod, testicular weight, serum testosterone concentrations, testosterone release from the luteinizing hormone (LH)-stimulated testis in vitro and sperm production were measured. Significant changes associated with seasonal cycles were found. Testis weight decreased dramatically in August, remained low until February, rapidly increased from March to high levels to June, and decreased subsequently. Serum testosterone concentrations remained little from August until February, but increased sharply in March to reach the highest levels in April. Thereafter, the concentrations decreased significantly from June. The testosterone release was low from August to February, increased abruptly in March to reach the highest levels in May, and showed rapid decrease thereafter. Sperm production decreased to nondetectable levels from August to February, increased markedly in March, reached a peak in May, and sharply decreased thereafter. Thus, the pheasants breed from late March to late June. These results indicate that the Korean ring-necked pheasant, under natural conditions, exhibits characteristics of a seasonal cycle in reproduction.

Testicular cycles in three species of Korean frogs: Rana nigromaculata, Rana rugosa, and Rana dybowskii

Seasonal changes in testicular structure and function in three species of Korean frogs (Rana nigromaculata, R. rugosa, and R. dybowskii) having different breeding seasons and habitats were examined throughout the year. R. nigromaculata live in rice fields and breed in early May. Their gonadosomatic index (GSI) and testis weight decreased slightly from May until July, but increased markedly from August to high levels through December. The diameter (cross-sectional area) of seminiferous tubules changed little from January until August, increased sharply from September through October, and decreased thereafter. In seminiferous tubules, the number of primary spermatogonia (I SPG) was low from January-March, increased from April to maximum levels by May-June, and decreased subsequently. The number of spermatids (SPT) was highest from November to March, decreased to nondetectable levels in May, and increased markedly from September to November. Spermiation was most active during March and April. R. rugosa, which live in streams and breed during May-June, exhibited no changes in GSI, testis weight, or seminiferous tubule size throughout the year. The number of I SPG was high during May-August and that of secondary spermatogonia (II SPG) was highest in August. The number of SPT increased to high levels in November-December. Active spermiation occurred from January to April in this frog. In R. dybowskii, which live in the mountains and breed from late February to early March, the number of I SPG gradually increased from April through August; however, essentially no other spermatogenic cells were observed from January to July. A marked increase in early spermatogenic cells appeared during August-September and was followed by an increase in SPT from November to December. From December to March the number of spermatozoa increased and spermiation occurred. In general, testicular testosterone levels were high in the winter and low in summer in all three species, and positively correlated with the number of interstitial cells and the size of their nucleus.

c-fos- and c-jun-like mRNA expression in frog (Rana esculenta) testis during the annual reproductive cycle

The expression of c-fos and c-jun mRNA has been examined in the testis of a seasonal breeder (the frog, Rana esculenta) during the annual reproductive cycle, using Northern blot analysis along with measurements of plasma levels of estradiol-17 beta and androgens (testosterone + 5 alpha-dihydrotestosterone). A c-fos-like transcript of 1.9 kb was revealed using a 1.1-kb v-fos probe, while three different transcripts of 3.7, 3.4, and 2.7 kb were seen using 1.0-kb human (h)-c-jun fragment. The proto-oncogene-like mRNAs appear during the period of the year associated with the new wave of spermatogenic activity. The levels of fos-like mRNA were highest after the estradiol-17 beta peak, while low levels were concomitant with high androgen concentrations. It is concluded that there is a close correlation between c-fos- and c-jun-like expression and testicular activity in R. esculenta.

Chicken GnRH-II and salmon GnRH effects on plasma and testicular androgen concentrations in the male frog, Rana esculenta, during the annual reproductive cycle

In the frog, Rana esculenta, two molecular forms of GnRH, coeluting with chicken (c) GnRH-II and salmon (s) GnRH, have been detected using HPLC and radioimmunoassay. Mammalian (m) GnRH seems to be also present. In amphibians the role of cGnRH-II seems to be primarily the involvement in the regulation of neuroendocrine processes and, while the mGnRH has been postulated to act as a neurotransmitter and/or neuromodulator, the activity of sGnRH-like material has not been investigated. Therefore, we have treated the frogs with single or multiple injections of cGnRH-II or sGnRH (6 micrograms) or both peptides (6 micrograms of each) to detect differences in the response measured as testicular or plasma androgen (testosterone plus 5 alpha-dihydrotestosterone) concentration during the annual reproductive cycle. The basal profile of testicular and plasma androgen shows that the spring peak disappeared in control animals given multiple injections and kept in short-term captivity. We show in the treatment with cGnRH-II and/or sGnRH that the effects of the peptides depend on the season, the experimental design, and the tissue in which androgen levels were measured. In particular, both peptides strongly stimulate androgen production during the autumn-winter period, the time of the greater response to the GnRHs when basal levels of steroids are highest.

Laryngeal muscle and motor neuron plasticity in Xenopus laevis: testicular masculinization of a developing neuromuscular system

In Xenopus laevis, the sexual differentiation of the neuromuscular system responsible for courtship song is controlled by testicular androgen secretion. To explore the sensitivity of this system to androgenic stimulation, male and female frogs were gonadectomized and given testis transplants at seven different developmental stages between the end of metamorphosis and adulthood, grown to sexual maturity, and the laryngeal muscle fibers and motor axons were counted. Muscle fiber and axon numbers in males were not affected by the testicular transplant at any stage. In females, testicular transplants at all developmental stages increased muscle fiber numbers in adulthood. Values attained were, however, significantly less than those of adult intact or testis-transplanted males. Testis transplantation increased laryngeal axon numbers in females to levels equivalent to those of intact males; this effect was obtained at every stage of postmetamorphic development including adulthood. To further explore androgen regulation in adults, males and females were gonadectomized and implanted with silicone tubes containing testosterone propionate for 1.5-3 years and laryngeal muscle fibers and axon numbers compared to those of gonadectomized or sham-operated adult controls. Neither treatment with exogenous androgen nor gonadectomy had any effect on laryngeal muscle fiber or axon number in either males or females; values did not differ from those of sham-operated controls. We conclude that testicular secretions can induce laryngeal muscle fiber and axon addition in females throughout postmetamorphic life. This degree of plasticity, exhibited after the period when adult values are normally attained, stands in contrast to the effects of administration of synthetic androgen and suggests that the degree of plasticity in adult females may be underestimated if exogenous hormones rather than testicular transplants are provided.

Two GnRHs fluctuate in correlation with androgen levels in the male frog Rana esculenta

ChickenII-(cII-) and salmon (s-) GnRH levels have been measured in the male frog Rana esculenta during the annual cycle. The presence of pituitary binding activity for both peptides and plasma androgen levels has been investigated in order to give insight into the significance of the dual control exerted by the GnRH forms present in the R. esculenta brain. ChickenII- and s-GnRHs showed high values during the spring-summer period. Conversely, while cII-GnRH peaked in February, s-GnRH declined slowly from February until May. Plasma androgen levels increased as the peptides decreased during the autumn-winter period. Still high androgen levels (but significantly lower as compared with winter concentrations) were found during spring. Using iodinated cII-GnRH, GnRH binding sites were detected in pituitary preparations when the corresponding peptide concentration decreased in the brain. On the contrary, no binding sites were found using labeled s-GnRH. Our results indicate that cII-GnRH has a hypophysiotropic activity, while the role of s-GnRH needs to be further investigated.

Seasonal fluctuations of androgen-binding activity in the testis of the frog, Rana esculenta

An androgen-binding activity has been identified in nuclear extracts of the testis of the frog, Rana esculenta. A single class of high affinity (Kd = 2.5 +/- 0.6 x 10(-9) M), low-capacity binding sites was found. The binding was specific for androgens; 17 beta-estradiol displaced [3H]testosterone with an ID50 of 0.1 microM. Cytosolic binding activity has a low affinity and a high capacity and lacks specificity. The seasonal fluctuations in binding capacity did not correlate with the androgen peaks in plasma and testes between February and June and in September; periods coinciding with the resumption of spermatogenesis and the development of spermatids, respectively. The present data strongly support androgenic control of intratesticular function in vertebrates generally.

Intratesticular control of spermatogenesis in the frog, Rana esculenta

Adult intact and hypophysectomized (PDX) frogs, Rana esculenta, were treated with a gonadotropin releasing hormone agonist (GnRHA, HOE 766) and/or cyproterone acetate (CPA), the antiandrogen, in order to investigate the regulation of primary spermatogonial (I SPG) multiplication in vertebrates. Treatment with GnRHA (injections containing 900 ng administered for 12 days on alternate days) caused a significant increase of the mitotic index (MI) of I SPG in PDX animals and a further MI increase of SPG was observed when 0.66 mg CPA was given concomitantly with GnRHA. The treatment with 0.66 mg CPA in combination with GnRHA also increased secondary spermatocyte (II SPC) appearance. Moreover, number of nests containing spermatids (SPT) decreased as CPA, in combination with GnRHA, was administered in increasing doses (0.33 and 0.66 mg/injection). Intact animals treated with CPA (0.66 mg/injection) showed a time-dependent I SPG multiplication increase which reached highest values after 28 days. Secondary SPC also proliferated until day 28; meanwhile the number of nests containing SPT decreased. Neither testosterone nor R5020 (a progestin which is not converted to androgens) modified the basal and GnRHA-induced spermatogonial proliferation. These results confirm that in the frog, Rana esculenta, spermatid formation is impaired by CPA treatment and that I SPG multiplication is enhanced by a direct effect of GnRHA; moreover, we suggest that the absence of spermatids constitutes a signal promoting spermatogonial proliferation.

Immunoreactive Met-enkephalin-like material in the testis of Rana esculenta: identification and localization

Methionine-enkephalin (Met-Enk) has been detected in the testis of the frog, Rana esculenta, using a reverse-phase high-performance liquid chromatography system coupled with a specific radioimmunoassay. By means of immunocytochemical techniques Met-Enk positive cells have been localized in interstitial and germinal compartments. Particularly, spermatogonia, spermatocytes, and spermatozoa were stained in seminiferous tubules, and numerous interstitial cells showed strong cytoplasmic immunoreactivity in summer animals. Variations in the concentration of Met-Enk immunoreactive material occurred during the annual cycle. Our data show that Met-Enk is present in testes of nonmammalian vertebrate species. These results suggest that autocrine and/or paracrine mechanisms may regulate testicular activity in amphibians.

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.

Effects of gonadotropin-releasing hormone variants on plasma and testicular androgen levels in intact and hypophysectomized male frogs, Rana esculenta

The effects of vertebrate gonadotropin-releasing hormone (GnRH) variants on plasma and testicular androgen level in intact and hypophysectomized (PDX) male frogs, Rana esculenta, have been investigated. In intact animals, mammalian (m)-GnRH, m-GnRH analog (buserelin), salmon (s)-GnRH, chicken (c) I-GnRH, cII-GnRH, D-Arg6-cII-GnRH (cII-GnRHA), and lamprey (l)-GnRH (1.5 micrograms and 6 micrograms, total dose given on alternate days for 5 days) were able to enhance androgen production showing that specificity of pituitary responsiveness to GnRH variants appears to be low. Chicken II-GnRH was more effective than s-GnRH in eliciting testicular and circulatory androgen level increase. Moreover, in animals treated with 6 micrograms of cII-GnRH and s-GnRH in combination, androgens decreased as compared with animal treated with cII-GnRH only, suggesting that GnRH receptors bind preferentially the s-GnRH form. In PDX animals, buserelin (1.5 and 6 micrograms), cII-GnRH, and its analog (6 micrograms) were able to increase plasma androgen levels whereas testis androgen concentrations were increased by cII-GnRH (1.5 and 6 micrograms), D-Arg6-cII-GnRHA, and buserelin (6 micrograms). Since androgen production in PDX animals is influenced especially by peptides sharing cII-GnRH structure, it is suggested that a testicular cII-GnRH-like material play a role as local modulator of the gonadal activity in Rana esculenta.

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

The present study was carried out to evaluate the in vitro effects of mammalian gonadotropin-releasing hormone (mGnRH) on the production of prostaglandin F2 alpha (PGF2 alpha) and sex steroids (progesterone, androgens, and 17 beta-estradiol) by the interrenal gland of male and female Rana esculenta during three different periods of the sexual annual cycle. In both sexes, mGnRH induced a significant increase in PGF2 alpha in the incubation medium in all examined periods. Progesterone and androgens were undetectable, while 17 beta-estradiol was significantly increased by mGnRH in interrenals incubated during the postreproductive period in both sexes. These results suggest that R. esculenta interrenals could be a GnRH-dependent PGF2 alpha-secreting tissue. In addition, the simultaneous increase in PGF2 alpha and estradiol from postreproductive cultured interrenals support the notion that mGnRH-induced estradiol synthesis is mediated through PGF2 alpha formation. This finding, taken together with other previous studies, strongly suggests that the end of the breeding period in R. esculenta depends on GnRH-induced PGF2 alpha-mediated enhancement of estradiol synthesis in a steroidogenetic organ (probably interrenals).

Effects of mammalian gonadotropin-releasing hormone on plasma level of prostaglandin F2 alpha in the water frog, Rana esculenta

The present investigation was performed to evaluate the effects of mammalian gonadotropin-releasing hormone (mGnRH) on prostaglandin F2 alpha (PGF2 alpha) plasma level in adult male and female water frog, Rana esculenta, during three different periods of the reproductive cycle: recovery period (October), breeding period (May), and postreproductive period (June). Intact, hypophysectomized (HYP), gonadectomized (GON), and hypophysectomized-and-gonadectomized (HYP/GON) animals were injected with 0.6 micrograms of mGnRH and sacrificed 1 hr and 5 hr after peptide administration. Some of each of the groups were sacrificed without having received mGnRH. PGF2 alpha plasma levels were assessed by radioimmunoassay. Hypophysectomy induced a significant increase of PGF2 alpha levels in October and June males. mGnRH induced a significant increase of PGF2 alpha plasma levels only in HYP and HYP/GON frogs. The tissue target of this GnRH action is, at present, unknown, although interrenals could be putative responsive tissues. At present, it is also difficult to assign any physiological role to observed phenomena unless to suppose that the pituitary inhibition is not constant throughout the year. It cannot be excluded that the prostaglandin induction depends on a local paracrine action of GnRH, which could be performed outside any pituitary control.

In vitro steroid production by follicles of frog Rana esculenta: mammalian gonadotropin-releasing hormone effects

The effects of mammalian gonadotropin-releasing hormone on ovarian release of progesterone, androgens and estradiol-17 beta were studied in vitro by a superfusion system carried out on follicles of adult female Rana esculenta, collected at different periods of the annual reproductive cycle. The follicles were superfused with medium alone, pituitary, mammalian gonadotropin-releasing hormone, or pituitary plus mammalian gonadotropin-releasing hormone. For follicles obtained in the prereproductive period, pituitary plus mammalian gonadotropin-releasing hormone increased the estradiol values much more than pituitary alone. In the reproductive period, pituitary alone increased the estradiol values much more than pituitary plus mammalian gonadotropin-releasing hormone. For follicles obtained in the recovery period, mammalian gonadotropin-releasing hormone alone stimulated the highest estradiol production, and pituitary plus mammalian gonadotropin-releasing hormone increased the estradiol values much more than pituitary alone. The results reported here suggest that mammalian gonadotropin-releasing hormone and/or pituitary have a direct effect on ovarian estradiol secretion, and that this effect varies with the annual reproductive cycle.

Sites of action of local estradiol feedback mechanism in the frog (Rana esculenta) testis

The direct effect of estradiol on testicular androgen biosynthesis was studied in the frog, Rana esculenta, measuring progesterone, 17 alpha-OH-progesterone, androstenedione, and androgens (T + DHT) in supernatants and testes incubated (6 hr, 15 degrees) with estradiol alone (10(-6) M) or in combination with crude pituitary homogenate (1 pituitary equivalent/tube). Estradiol, either alone or in combination with pituitary homogenate, induced decreases of 17 alpha-OH-progesterone, androstenedione, and androgens but was ineffective in modulating progesterone levels. Pituitary homogenate was effective in inducing a significant increase of androstenedione and androgens but was ineffective in modulating both progesterone and 17 alpha-OH-progesterone production. It is concluded that estradiol acts by decreasing the activity of steroidogenic enzymes starting from 17 alpha-hydroxylase, while pituitary homogenate does not affect the 17 alpha-hydroxylase activity, but it acts starting from 17,20-lyase.

Regulation of the testicular activity in the marine teleost fish, Gobius paganellus

Seasonal variations of intratesticular steroid hormones (androgens and estradiol-17 beta) and spermatogenic activity have been studied in the marine teleost fish, Gobius paganellus. In addition, in vivo and in vitro experiments have been carried out in order to investigate the control of androgen production by the testis. While estradiol was never detected, androgens were at low values in autumn and reached maximal levels in spring concomitantly with the highest testis weight and the highest efficiency of the spermatogenic wave. In vitro incubations were carried out using ovine luteinizing hormone (oLH) (400, 4000, and 40,000 micrograms/liter; 20 degrees for 6 and 24 hr). The effective dose 40,000 micrograms/liter was used to induce androgen stimulation in both autumn and spring testes. The responsiveness to oLH was enhanced in spring testis. Estradiol and a gonadotropin-releasing hormone analog GnRHA (HOE766) were ineffective in modulating androgen production either alone (1-1000 nmol/liter) or in concert with oLH during short-term incubations. In intact animals, GnRHA elicited, 3 hr after the injection (10 micrograms), a three-fold increase of intratesticular androgen content. In conclusion, we show that the annual androgen profile in G. paganellus parallels the spermatogenic activity and that the androgen production is not affected in these experimental conditions by putative intratesticular factors (e.g., estradiol-17 beta and GnRH-like substances) which, conversely, are effective in inducing androgen changes in several vertebrate species.