Opposing effects of D-aspartic acid and nitric oxide on tuning of testosterone production in mallard testis during the reproductive cycle

D-Aspartic acid (D-Asp) and nitric oxide (NO) play an important role in tuning testosterone production in the gonads of male vertebrates. In particular, D-Asp promotes either the synthesis or the release of testosterone, whereas NO inhibits it. In this study, we have investigated for the first time in birds the putative effects of D-Asp and NO on testicular testosterone production in relation to two phases of the reproductive cycle of the adult captive wild-strain mallard (Anas platyrhynchos) drake. It is a typical seasonal breeder and its cycle consists of a short reproductive period (RP) in the spring (April-May) and a non reproductive period (NRP) in the summer (July), a time when the gonads are quiescent. The presence and the localization of D-Asp and NO in the testis and the trends of D-Asp, NO and testosterone levels were assessed during the main phases of the bird's reproductive cycle. Furthermore, in vitro experiments revealed the direct effect of exogenously administered D-Asp and NO on testosterone steroidogenesis.

METHODS

By using immunohistochemical (IHC) techniques, we studied the presence and the distributional pattern of D-Asp and NO in the testes of RP and NRP drakes. D-Asp levels were evaluated by an enzymatic method, whereas NO content, via nitrite, was assessed using biochemical measurements. Finally, immunoenzymatic techniques determined testicular testosterone levels.

RESULTS

IHC analyses revealed the presence of D-Asp and NO in Leydig cells. The distributional pattern of both molecules was in some way correlated to the steroidogenic pathway, which is involved in autocrine testosterone production. Indeed, whereas NO was present only during the NRP, D-Asp was almost exclusively present during the RP. Consistently, the high testosterone testicular content occurring during RP was coupled to a high D-Asp level and a low NO content in the gonad. By contrast, in sexually inactive drakes (NRP), the low testosterone content in the gonad was coupled to a low D-Asp content and to a relatively high NO level. Consequently, to determine the exogenous effects of the two amino acids on testosterone synthesis, we carried out in vitro experiments using testis sections deriving from both the RP and NRP. When testis slices were incubated for 60 or 120 min with D-Asp, testosterone was enhanced, whereas in the presence of L-Arg, a precursor of NO, it was inhibited.

CONCLUSION

Our results provide new insights into the involvement of D-Asp and NO in testicular testosterone production in the adult captive wild-strain mallard drake. The localization of these two molecules in the Leydig cells in different periods of the reproductive cycle demonstrates that they play a potential role in regulating local testosterone production.

d-Aspartic acid and nitric oxide as regulators of androgen production in boar testis

D-Aspartic acid (D-Asp) and nitric oxide (NO) are two biologically active molecules playing important functions as neurotransmitters and neuromodulators of nerve impulse and as regulators of hormone production by endocrine organs. We studied the occurrence of D-Asp and NO as well as their effects on testosterone synthesis in the testis of boar. This model was chosen for our investigations because it contains more Leydig cells than other mammals. Indirect immunofluorescence applied to cryostat sections was used to evaluate the co-localization of D-Asp and of the enzyme nitric oxide synthase (NOS) in the same Leydig cells. D-Asp and NOS often co-existed in the same Leydig cells and were found, separately, in many other testicular cytotypes. D-Asp level was dosed by an enzymatic method performed on boar testis extracts and was 40+/-3.6 nmol/g of fresh tissue. NO measurement was carried out using a biochemical method by NOS activity determination and expressed as quantity of nitrites produced: it was 155.25+/-21.9 nmol/mg of tissue. The effects of the two molecules on steroid hormone production were evaluated by incubating testis homogenates, respectively with or without D-Asp and/or the NO-donor L-arginine (L-Arg). After incubation, the testosterone presence was measured by immunoenzymatic assay (EIA). These in vitro experiments showed that the addition of D-Asp to incubated testicular homogenates significantly increased testosterone concentration, whereas the addition of L-Arg decreased the hormone production. Moreover, the inclusion of L-Arg to an incubation medium of testicular homogenates with added D-Asp, completely inhibited the stimulating effects of this enantiomer. Our results suggest an autocrine action of both D-Asp and NO on the steroidogenetic activity of the Leydig cell.

Involvement of D-Asp in P450 aromatase activity and estrogen receptors in boar testis

Mammalian testis contains D-aspartic acid (D-Asp), which enhances testosterone production. D-Asp, on other hand, also stimulates 17beta-estradiol synthesis in the ovary of some lower vertebrates. We studied boar testis in order to determine if D-Asp intervenes in 17beta-estradiol synthesis in the testis of those mammals which produce significant amounts of estrogens as well as testosterone. The boar testis contains D-Asp (40 +/- 3.6 nmol/g tissue) which, according to immunohistological techniques, is localized mainly in Leydig cells, and, to a lesser extent, in sustentacular (Sertoli), peritubular and some germ cells. The enzyme P450aromatase is present in Leydig cells and few germ cells. In vitro experiments showed that the addition of D-Asp to testicular tissue extracts induced a significant increase of aromatase activity, as evaluated by testosterone conversion into 17beta-estradiol. The enzyme's K(m) was not affected by D-Asp (about 25 nM in both control and D-Asp added tests). On the basis of these results we suggest that, as in the ovary, D-Asp is involved in the local control of aromatase activity of boar testis and, therefore, it intervenes in the 17beta-estradiol production. In the testis, the D-Asp targets are presumably the Leydig cells, which having also a nuclear estrogen receptor are, in turn, one of the putative targets of the 17beta-estradiol that they produce (autocrine effect).

Endogenous testicular D-aspartic acid regulates gonadal aromatase activity in boar

D-aspartic acid (D-Asp), aromatase enzyme activity and the putative D-Asp involvement on aromatase induction have been studied in the testis of mature boars. The peroxidase-antiperoxidase and the indirect immunofluorescence methods, applied to cryostat and paraffin sections, were used to evaluate D-Asp and aromatase distributions. D-Asp level was dosed by an enzymatic method performed on boar testis extracts. Biochemical aromatase activity was determined by in vitro experiments carried out on testis extracts. D-Asp immunoreactivity was found in Leydig cells, and, to a lesser extent, in germ cells. Analogously, aromatase immunoreactivity was present in Leydig cells, but absent from seminiferous tubule elements. In vitro experiments showed that the addition of D-Asp to testicular tissue acetone powder induced a significant increase of aromatase activity, as assessed by testosterone conversion to 17beta-estradiol. Enzyme Km was not affected by D-Asp (about 25 nM in control and D-Asp added tests). These findings suggest that D-Asp could be involved in the local regulation of aromatase in boar Leydig cells and intervenes in this organ's production of estrogens.

Testicular endocrine activity is upregulated by D-aspartic acid in the green frog, Rana esculenta

This study investigated the involvement of D-aspartic acid (D-Asp) in testicular steroidogenesis of the green frog Rana esculenta and its effect on stimulation of thumb pad morphology and glandular activity, a typical testosterone-dependent secondary sexual characteristic in this amphibian species. In the testis, D-Asp concentrations vary significantly during the reproductive cycle: they are low in pre- and post-reproductive periods, but reach peak levels in the reproductive period (140-236 nmol/g wet tissue). Moreover, the concentrations of D-Asp in the testis through the sexual cycle positively match the testosterone levels in the gonad and the plasma. The racemase activity evaluated during the cycle expresses its peak when D-Asp and testosterone levels are highest, that is, during the reproductive period, confirming the synthesis of D-Asp from L-Asp by an aspartate racemase. Short-term in vivo experiments consisting of a single injection of D-Asp (2.0 micro mol/g body weight) demonstrated that this amino acid accumulates significantly in the testis, and after 3 h its uptake is coupled with a testosterone increase in both testis and plasma. Moreover, within 18 h of amino acid administration, the D-Asp concentration in the testis decreased along with the testosterone titer to prestimulation levels. Other amino acids (L-Asp, D-Glu and L-Glu) used instead of D-Asp were ineffective, confirming that the significant increase in testicular testosterone was a specific feature of this amino acid. In long-term experiments, D-Asp had been administered chronically to frogs caught during the three phases of the reproductive cycle, inducing testosterone increase and 17beta-estradiol decrease in the gonad during the pre- and post-reproductive period, and vice versa during the reproductive period. The stimulatory effect of D-Asp on testosterone production by the testis is consistent with the stimulation of spermatogenesis and the maturation of thumb pads occurring in D-Asp-treated frogs. In these last animals, there was an increase of seminiferous ampoule area and a higher number of spermatids and sperm. Moreover, in spermatogonia I and II and in spermatocytes, a proliferating cell nuclear antigen (PCNA) intense immunopositivity was observed. In addition, the thumb pads of D-Asp-treated frogs compared with controls showed a significantly thicker epithelial lining, a wider area of their glands with taller secretion cells, and more numerous, PAS-positive-rich secretions. Finally, these results provide functional evidence for a biologic role of D-Asp in amphibian male steroidogenesis; therefore, this unusual amino acid could be considered a modulatory agent for reproductive processes.

NADPH-d positive neurons of the lizard Podarcis s. sicula oviduct and their relationship to 17beta-estradiol hormone

The distribution of nicotinamide adenine dinucleotide phosphate reduced diaphorase (NADPH-d) containing neurons was examined in the oviduct of the lizard Podarcis s. sicula and the relationship between these neurons and 17beta-estradiol hormone was studied. NADPH-d-histochemistry and indirect immunofluorescence method were applied to cryostat sections. NADPH-d-nerve structures were found throughout the oviduct. Positive neurons were primarily located in the reproductive oviduct, and were more numerous in the intermuscular and circular muscle layers than in the mucosa. The vagina revealed a reactive nerve population denser than elsewhere. The NADPH-d-positive neurons densities and the 17beta-estradiol plasma levels coincided throughout the lizard sexual cycle. In addition, after 17beta-estradiol treatments, non-reproductive lizards showed an increase of NADPH-d neurons. We suppose that nitric oxide (NO) neurons play an estrogen-dependent role in the oviduct muscle motility.

Enhancement of aromatase activity by D-aspartic acid in the ovary of the lizard Podarcis s. sicula

The present study investigated the role of D-aspartic acid (D-Asp) in ovarian steroidogenesis and its effect on aromatase activity in the lizard, Podarcis s. sicula. It was determined that D-Asp concentrations vary significantly during phases of the reproductive cycle: they vary inversely with testosterone concentrations and directly with oestradiol concentrations in the ovary and plasma. Experimental treatment showed that administration of D-Asp induces a decrease in testosterone and an increase in oestradiol, and that treatment with other amino acids (L-Asp, D-Glu and D-Ala) instead of D-Asp has no effects. Experiments in vitro confirmed these results. Furthermore, these experiments showed an increase in aromatase activity, as the addition of D-Asp either to fresh ovarian tissue homogenate or to acetonic powder of ovarian follicles induced a significant increase in the conversion of testosterone to oestradiol. Aromatase activity is four times greater in the presence of D-Asp than in its absence. However, almost equivalent values of the two K(m) values (both approximately 25 nmol l(-1)) indicate that aromatase has the same catalytic properties in both cases.

TrkA and TrkC neurotrophin receptor-like proteins in the lizard gut

The tyrosine kinase proteins (Trk), encoded by the trk family of proto-oncogenes, mediate, in mammals, the action of neurotrophins, a family of growth factors acting on the development and maintenance of the nervous system. Neurotrophins and their specific receptors, TrkA, TrkB and TrkC, seem to be phylogenetically well preserved but, in reptiles, data regarding the occurrence of Trk-like proteins are very scarce, especially in non-nervous organs. Western blot analysis demonstrated that the lizard gut contains TrkA- and TrkC-like, but not TrkB-like, proteins. Consistently, TrkA- and TrkC-like immunoreactivity were both observed in neurons of the anterior intestine, whereas endocrine cells of the stomach and anterior intestine only displayed TrkA-like immunoreactivity. These results demonstrate for the first time the occurrence of Trk-like proteins in non-neuronal tissues of reptilians and provide further evidence for the evolutionary preservation of the molecular mass and cell distribution of Trk neurotrophin receptor-like proteins in the gut of vertebrates.

The relationships of nicotinamide adenine dinucleotide phosphate-d to nitric oxide synthase, vasoactive intestinal polypeptide, galanin and pituitary adenylate activating polypeptide in pigeon gut neurons

The distribution of nicotinamide adenine dinucleotide phosphate (NADPH)-d neurons and their relationship with nitric oxide synthase (NOS), vasoactive intestinal polypeptide (VIP), pituitary adenylate activating polypeptide (PACAP) and galanin (Gal) were examined in the gastrointestinal (GI) tract of the pigeon Columbia livia. NADPH-d-histochemistry, indirect immunofluorescence and confocal analysis were applied to cryosections. Western blot analysis was also applied on pigeon gut. NADPH-d neurons were found throughout the pigeon GI tract and they were evident in the myenteric, circular muscle and submucous plexuses. Positive varicose nerve fibres were also distributed within the longitudinal muscle layers and in the lamina propria of the mucosa. The stomach was the segment richest in positivities. The copresence VIP/Gal/NOS as well as PACAP/VIP were revealed in some NADPH-d-neurons. We suppose that the nitrergic nerve population of the pigeon GI tract belong to the muscle motility regulation as an inhibitory descending nerve pathway. Moreover the presence of VIP, Gal and PACAP in some NADPH-d-containing neurons enhances the inhibitory actions of these neurotransmitters whereas PACAP and Gal role is actually unknown.

Estrogen receptors and aromatase activity in the hypothalamus of the female frog, Rana esculenta. Fluctuations throughout the reproductive cycle

It is well known that certain actions of androgen are mediated through in situ aromatization to estrogen in neural target tissues. This study was undertaken to investigate androgen utilization in the hypothalamus of the female frog, Rana esculenta, through a quantification of estrogen receptors and aromatase activity during the reproductive cycle. 3H-estradiol-binding molecules were present in both the cytosol and the nuclear extract of the hypothalamus. These molecules bound specifically 3H-estradiol with high affinity (Kd 10(-10) M) and low capacity (cytosol: 1.2+/-0.4 fmol/mg protein; nuclear extract: 7.9+/-0.6 fmol/mg protein). Aromatase activity was detected in the microsomal fraction of the hypothalamus using a sensitive in vitro radiometric assay. Both aromatase activity and nuclear estrogen receptor binding fluctuated in synchrony throughout the reproductive cycle. Western blot analysis of aromatase protein revealed one immunoreactive band with a molecular weight of approximately 56 kDa. In contrast to aromatase enzyme activity, the relative levels of aromatase protein changed little during the reproductive cycle suggesting that post-translational mechanisms may be involved in regulating estrogen synthesis in the frog brain. A possible role for estrogens in the modulation of the reproductive behavior in this species is suggested.

Relationships between liver testosterone receptor isoforms and aromatase activity in female green frog, Rana esculenta

Testosterone receptors (AR) are present in the liver of the female green frog, Rana esculenta, which resolve into two fractions (A and B) by ion-exchange chromatography. Fraction A is primarily located in the nuclei, fraction B predominates in the cytosols, and both fractions show a high affinity and specificity for testosterone. Liver AR fraction levels vary dramatically during the frog sexual cycle. Fraction A levels are high only when the liver is engaged in vitellogenin production and the plasma testosterone levels are high: they are maximal when aromatase activity is most intense. Fraction B levels are high when the liver is not producing vitellogenin and the plasma testosterone levels are minimal. In addition, in vivo experiments carried out on ovariectomized females treated with testosterone show that testosterone induces both fraction A and liver aromatase activity. This induction may be a step in the process that allows the liver to obtain estrogen from plasma testosterone which induces vitellogenin synthesis.

Mammalian and chicken I forms of gonadotropin-releasing hormone in the gonads of a protochordate, Ciona intestinalis

Two forms of gonadotropin-releasing hormone (GnRH) were isolated from the gonads of the tunicate, Ciona intestinalis. The primary structure of the purified peptides was determined by MS and chemical sequence analysis. Both GnRH forms have blocked NH(2) and COOH termini, and their primary structures are identical to mammalian (mGnRH) and chicken I (cGnRH-I) forms reported previously in vertebrates. A total of 1.2 mg of purified cGnRH-I and 0.98 mg of mGnRH was obtained from 100 g of Ciona gonads. The physiological effects of native GnRHs included the induction of synthesis and secretion of sex steroids from ciona gonads and the secretion of luteinizing hormone from rat pituitary. These results suggest that the primary structure and functional roles of mGnRH and cGnRH-I have been highly conserved throughout evolution of chordates.

Galanin in the lizard oviduct: its distribution and relationships with estrogen, VIP and oviposition

The distribution of neurons containing galanin immunoreactivity (Gal/IR) has been detected in the oviduct of the lizard Podarcis s. sicula during the main phases of its sexual cycle and after 17beta-estradiol treatment. Indirect immunofluorescence technique was applied both to cryostatic sections and whole mount preparations, and Western blot analysis, with an antibody directed against mammalian galanin (Gal), was performed with lizard oviduct extracts. Colocalization of Gal with vasoactive intestinal polypeptide (VIP) was also studied as well as Gal effects on egg deposition. In the quiescent oviduct of non-reproductive females, scanty Gal/IR fibres were found in the uterine-vaginal segment. During the reproductive period a gradual increase of positive nerve fibres and cell bodies were found distally in the lizard oviduct and the vagina revealed a reactive nerve population denser than elsewhere. Gal-IR nerve structures were present either in the musculature or mucosa and in the intermuscular layer they were organized in a nerve network. In the oviduct of non-reproductive females, 17beta-estradiol administration induced a significant increase of neurons containing Gal/IR. This hormone could be involved in the egg laying by means of galanin action and this hypothesis is supported by the induction of premature oviposition in pre-ovulatory females after Gal administration. Western blot analysis validates this peptide as true Gal, recognising one protein band with a molecular weight (3.2 kDa), similar to that of porcine Gal. Double labelling studies showed the co-presence of Gal and VIP in some neurons.

Galanin-containing-neurons, in the gastrointestinal tract of the lizard Podarcis s. sicula, as components of anally projecting nerve pathway

The distribution of galanin immunoreactive (Gal/IR) neurons was investigated in the gastrointestinal (GI) tract of the lizard Podarcis s. sicula. The indirect immunofluorescence method, image analysis and confocal analysis were applied to cryostat sections and whole mount preparations. Gal/IR nerve fibers and cell bodies were found throughout the lizard GI tract in the myenteric plexus, circular muscle layer and mucosa. These nerve structures decreased caudally. The stomach revealed a denser reactive nerve population than elsewhere. The projections of Gal/IR neurons were detected in the myenteric plexus of lizard gut using a confocal microscope which analyzed the immunoreactive material on the proximal and distal sides of muscle myotomies. An accumulation of Gal/IR material on the oral side of the myotomies demonstrated the oral-to-anal projection of Gal containing nerve structures. Based on our results, it can be hypothesized that Gal/IR neurons of the lizard digestive tract belong to the inhibitory descending pathway, which in most vertebrates is responsible for gut peristalsis regulation.

NADPH-diaphorase and NOS enzymatic activities in some neurons of reptilian gut and their relationships with two neuropeptides

The distribution of neurons containing the enzymes NADPH-diaphorase (NADPH-d) and nitric oxide synthase (NOS) has been studied in the gastrointestinal tract of lizard (Podarcis s. sicula) and snake (Thamnophis sirtalis). The techniques employed were the NADPH-d/nitroblue tetrazolium histochemical method, and the indirect immunofluorescence applied to cryostat sections and to whole-mount preparations. The colocalization of NADPH-d with NOS, with vasoactive intestinal polypeptide (VIP) and with galanin (Gal) was also studied, and a Western blot analysis using an antibody directed against mammalian Gal was performed on lizard stomach extracts. NADPH-d positive nerve cell bodies and fibres were found in the myenteric and submucous plexuses throughout the gastrointestinal tract of both reptiles. These nerve structures were also present in the other intramural nerve plexuses, although in smaller quantities. Both in lizard and snake, the stomach revealed a positive nerve population that was more dense than elsewhere in the gut. The population of the NADPH-d-positive neurons observed in the lizard was larger than that observed in the snake. The distribution of both populations was similar to those that have been described in the gut of several mammalian and non-mammalian vertebrates. Both in lizard and snake, a one-to-one correspondence was noted between NOS- and NADPH-d-containing nerve cell bodies, and the nitrergic neurons containing Gal appeared to be more numerous than those containing VIP. Western blot analysis recognised a single band with a molecular weight (3.4 kDa) very similar to that of porcine Gal. It is hypothesised that at least some of the nitrergic neurons of the lizard and snake gut are inhibitory motor neurons innervating the circular smooth musculature. In addition, the colocalization of NOS and VIP in neurons enhances their inhibitory action. The role of the neurons containing both NOS and Gal remains unknown.

Hormonal control of "tissue" transglutaminase induction during programmed cell death in frog liver

In this study, we show that sex hormones (testosterone, estradiol, and progesterone) act as physiological modulators of programmed cell death (PCD) during the frog liver involution observed postvitellogenesis. PCD in parenchymal cells is paralleled by the specific induction of the "tissue" transglutaminase (tTG) gene. tTG protein specifically accumulates in hepatocytes showing the morphological features of apoptosis. The hormone-dependent increase of both PCD and tTG was reproduced in ovariectomized frogs. Treatment of castrated animals with testosterone, estradiol, and progesterone inhibited the induction of both tTG and PCD, thus indicating that in vivo the drop in the circulating sex hormone is the signal favoring the involution phase of the maternal frog liver after mating. Although an affinity-purified polyclonal antibody raised against mammalian transglutaminase reacts in frog liver with a 55- to 60-kDa protein, concomitant with the onset of PCD, tTG cleavage products were detected, suggesting a proteolytic processing of the enzyme protein. These results represent the first evidence indicating that the physiological involution occurring postvitellogenesis of frog liver takes place by programmed cell death and that this, together with the concomitant induction of tTG gene expression, is regulated by sex hormones.

Progesterone receptor in the reproductive system of the female of Octopus vulgaris: characterization and immunolocalization

In this study for the first time we have characterized a progesterone receptor in the reproductive system of the female of Octopus vulgaris. Scatchard analysis revealed that one binding component with high affinity and low capacity for the ligand was present only in the nuclear extract. Competition experiments showed that the progesterone receptor was strictly specific for progesterone. DNA-cellulose binding and DEAE-Sephacel both confirmed the presence of one 3H-progesterone binding component which eluted at a salt concentration of 0.14 +/- 0.05 M NaCl and 0.15 +/- 0.05 M NaCl respectively. By using monoclonal antibodies against chicken progesterone receptor (subunits A and B), we have localized on Western Blot one band of about 70 kDa. Immunoreactivity for progesterone binding molecules has been localized in the nuclei of the follicle cells of the ovary, of the proximal portion of the oviduct and of the outer region of the nidimental gland. These data, taken together, provide evidence that in Octopus vulgaris the progesterone receptor has biochemical and immunohistochemical characteristics resembling those of progesterone receptor in vertebrates.

Aromatase and testosterone receptor in the liver of the female green frog, Rana esculenta

In the green frog, Rana esculenta, a peculiar feature of female reproductive endocrinology is an high level of circulating testosterone. Although several hypotheses have been set out to explain this phenomenon, the testosterone specific roles in female anuran have not been yet fully explored. This study results propose a testosterone implication in liver vitellogenin synthesis control, since in ovariectomized frogs the hormone induces an increase of circulating vitellogenin. The testosterone action could depend on its local conversion to 17beta-estradiol by aromatase which is present in frog liver tissue. Liver aromatase activity ranges from 7.5 to 26 fmoles E2 formed/mg protein/h and results higher as long as liver is engaged in vitellogenin synthesis. Aromatase activity seems depend on testosterone since it decreases after ovariectomy and is restored by testosterone injection in ovariectomized frogs. In green frog liver, testosterone binding molecules are present both in cytosol and nuclei. These molecule binding properties (Kd and Bmax in nM range; t 1/2 = 85 min; specificity) are in line with those of testosterone receptor of other lower vertebrate target tissue. In liver nuclei, testosterone receptor level undergoes modification throughout the sexual cycle which almost coincides with that of plasma testosterone level and liver aromatase activity. This could indicate that the testosterone induction of liver aromatase in frogs is via the testosterone receptor, as reported for aromatase of mammalian brain tissues.

D-aspartic acid is implicated in the control of testosterone production by the vertebrate gonad. Studies on the female green frog, Rana esculenta

In the present study we report the occurrence of D-aspartic acid (D-Asp) in the ovary of the green frog Rana esculenta and its putative involvement in testosterone production by the gonad. In the ovary, D-Asp concentrations undergo significant variations during the main phases of the sexual cycle. In spawning females (March), its concentration was low (2.5 +/- 1.1 nmol/g ovary) and during the post-reproductive period (June) it increased and reached its peak level (58.0 +/- 10.1 nmol/g) in October. In that month, vitellogenesis occurs in a new set of ovarian follicles and continues until the next spring. The concentrations of D-Asp in the ovary and of testosterone in the ovary and in the plasma were inversely correlated during the reproductive cycle: when endogenous D-Asp was low (March), testosterone was high (36.9 +/- 4.8 ng/g ovary; 23.1 +/- 2.76 ng/ml plasma) and, in contrast, when the D-Asp concentration was high (October), the testosterone concentration was low (0.86 +/- 0.21 ng/g ovary and 5.0 +/- 1.3 ng/ml plasma). In vivo experiments, consisting of injection of D-Asp (2.0 mumol/g body weight) into the dorsal lymphatic sac of adult female frogs, demonstrated that this amino acid accumulates significantly in the ovary. After 3 h, moreover, it caused a decrease in testosterone level in the plasma of about 80%. This inhibition was reversible: within 18 h after the amino acid injection, as the D-Asp concentration in the ovary decreased, the testosterone titre was restored in both ovary and plasma. In vitro experiments, conducted in isolated ovarian follicles, confirmed this phenomenon and identified these gonadal components as the putative D-Asp targets. Other amino acids (L-Asp, D-Glu, L-Glu, D-Ala and L-Ala) used instead of D-Asp were ineffective. These findings indicate that D-Asp is involved in the control of androgen secretion by the ovary in this amphibian species, revealing a more complex system for control of this androgen synthesis than was previously believed to exist.

Apolipoproteins and their electrophoretic pattern throughout the reproductive cycle in the green frog Rana esculenta

Lipoprotein fractions in Rana esculenta were separated using the same salt intervals currently applied for human lipoproteins. Very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) were analyzed with reference to the electrophoretic pattern. The lipoprotein electrophoretic pattern in males and females throughout the reproductive cycle showed minor differences. In general, each fraction was characterized by a specific apolipoprotein content. VLDL and LDL fractions were dominated by a high molecular weight (MW) band, most likely the counterpart of human Apolipoprotein B (apo B). The apo B in R. esculenta cross reacted, although weakly, with antibodies raised against chicken apo B. The HDL fraction showed a band with an apparent MW of 29 kDa. The electrophoretic mobility of the protein moiety of HDL was similar to human apolipoprotein A-I (apo A-I). However, HDL apolipoprotein of R. esculenta did not cross react with antibodies against chicken apo A-I under either denaturing or native conditions. The HDL apolipoprotein of R. esculenta was purified by DEAE-Sephacel chromatography followed by HPLC. Its amino acid composition showed a moderate correlation with trout, salmon, chicken and human apo A-I.

In vitro effects of beta-endorphin on testicular release of androgens in the lizard Podarcis sicula Raf

The effects of the proopiomelanocortin-derived opioid peptide, beta-endorphin (beta-EP), and of the opioid antagonist, naloxone (NAL), on both basal and pituitary-stimulated androgen secretion from superfused quiescent and active testes were assessed in the adult lizard, Podarcis sicula. In the absence of the homologous pituitary, in vitro treatment with beta-EP and/or NAL did not affect basal secretion of androgens from quiescent and active testes. Conversely, in the presence of the homologous pituitary, treatment with beta-EP brought about a decrease in androgen secretion in active testes, but no effect on quiescent ones. Naloxone counteracted the inhibitor effect of beta-EP in active testes, and enhanced maximal pituitary-stimulated secretion of androgens in quiescent but not in active testes. The effects produces by beta-endorphin and naloxone were reversible. These results suggest that, in this lizard, opioids might be involved in the control of androgen release. The lack of effect of beta-EP and naloxone when added directly to the testes seems to suggest that the opioid agonist and antagonist act on androgen release by modulating pituitary gonadotrophin output.

Occurrence of sex steroid hormones and their binding proteins in Octopus vulgaris lam

The present study reports the presence of progesterone, testosterone and 17 beta-estradiol and their corresponding binding proteins in the reproductive system of Octopus vulgaris Lam (phylum Mollusca, subphylum Cephalopoda). These sex hormones occur in testis, vas deferens, seminal vesicle, prostate and Needham's sac. The hemolymph also contains a small, but significant, amount of these hormones and their carrier proteins. Among various tissues of the reproductive system, the seminal vesicle possesses the highest concentration of progesterone (4.8 ng/g tissue). The testis is the organ which contains the highest amount of testosterone (5.2 ng/g) whereas the prostate is the organ which contains the highest amount of 17 beta-estradiol (0.92 ng/g). The presence of these hormones has been ascertained by a radioimmunoassay method, an immunoenzymatic method and by a chemical (HPLC) method. Seatchard studies indicated that vas deferens and seminal vesicle contain specific sex steroid binding molecules at affinity levels comparable to those of vertebrate steroid receptors (0.5-5.0 pmol/g protein). In addition to the presence of the hormones, the delta 5,3 beta hydroxysteroid dehydrogenase, the key enzyme of steroidogenesis, also is found in testis. From a phylogenetic point of view, these findings are very interesting because they indicate a common origin of a sex hormonal system between Mollusca Cephalopoda and Vertebrates.

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.

PGF2 alpha, PGE2, progesterone, and estradiol-17 beta, secretion by the corpus luteum of the oviparous lizard, Podarcis sicula sicula. In vitro studies

The release in vitro of prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), progesterone, androgens and estradiol-17 beta by the corpora lutea (CL) of the oviparous lizard, Podarcis s. sicula, was studied. In addition, the in vitro effects of PGF2 alpha and PGE2 on sex steroid release by CL were evaluated. Corpora lutea were divided into four types, according to their different developmental stage: CL1 (unshelled eggs in the oviduct); CL2 (shelled eggs in the oviduct); CL3 (eggs laid 6 h previously); CL4 (eggs laid 48 h previously) and were placed into culture. PGF2 alpha secretion was highest in CL4 incubated samples and lowest in CL2 and PGE2 was highest in CL1 and CL2. Progesterone secretion was highest in CL2 and lowest in CL4; androgens were not detectable and estradiol-17 beta secretion was highest in CL2. PGF2 alpha decreased progesterone secreted by CL1, CL2 and CL3, while it did not modify release of androgens and estradiol-17 beta. PGE2 did not affect sex steroid release. These data suggest a role of PGF2 alpha in inducing luteolysis, while PGE2 could be implied in the maintenance of CL. A role of progesterone during gestation of Podarcis s. sicula was also confirmed.

Plasma sex steroid binding proteins (SSBP) in the male lizard, Podarcis s. sicula, during the reproductive cycle

In male Podarcis s. sicula plasma, a sex steroid binding protein [SSBP(s)] binds testosterone (T) and estradiol-17 beta (E2) with moderate affinity (Kd = 0.23 +/- 0.08 x 10(-8) for 3H-E2, and 0.24 +/- 0.07 x 10(-8) for 3H-T) and high capacity. The SSBP binding affinity is unchanged throughout the sexual cycle, although its capacity is higher in nonreproductive males (winter and postreproductive period). This change may be related to changes in plasma T and E2 levels, and is likely to be involved in mechanisms whereby free steroid is delivered to target organs. SSBP, under isoelectrofocusing, is distributed between pH 5.5-6.5 and pH 7.1-7.5. The concentration of these two forms varies during the annual cycle.

Sex steroids levels in the plasma and testis during the reproductive cycle of lizard Podarcis s. sicula Raf

Progesterone (P), 17-OH-progesterone (17-OH-P), androstenedione (A), dehydroepiandrosterone (DHEA), testosterone (T), 5 alpha-dihydrotestosterone (5 alpha-DHT), and 17 beta-estradiol (E2) were measured by RIA in plasma and testes of 114 males of the oviparous lizard Podarcis s. sicula raf, a species that displays annual hibernating cycles. Hormones were determined each month from January until December, except for August. Testosterone peaked at 174.8 ng/ml of plasma after emergence (March), while 5 alpha-DHT and A peaked in April. Plasma DHEA increased during hibernation. During the refractory period there were progressive increases in P and E2 plasma levels. The testicular peak of T, in March, coincided with that observed in plasma. The striking increases in testicular T and A in early July occurred at a time when plasma androgen concentrations were low. 5 alpha-DHT increased in April when spermatogenesis with spermiation occurred and then decreased alongside a second peak of T. There is an apparent separation of plasma and testicular androgen concentrations during the reproductive cycle.

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.

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.

Seasonal changes in plasma prostaglandin F2 alpha and sex hormones in the male water frog, Rana esculenta

Prostaglandin F2 alpha (PGF2 alpha), progesterone, androgens (testosterone + dihydrotestosterone), and 17 beta-estradiol were measured in the plasma of male frogs, Rana esculenta, by radioimmunoassays. Plasma concentrations of PGF2 alpha were higher from October to December and peaked in March (prereproduction) and in June (postreproduction). Plasma progesterone levels were relatively low but showed an increase from October to December and in June. Plasma androgen titres rapidly increased in early spring, started to fall during the reproductive period (May), and were lowest in July. 17 beta-Estradiol levels peaked in March and in June. The annual profile of the plasma PGF2 alpha levels was positively correlated with those of progesterone and androgens, while it was not correlated to the estradiol plasma pattern, except in March and June. The increase in plasma PGF2 alpha in the autumn may be related to gonadal recovery. The simultaneous increases in PGF2 alpha and 17 beta-estradiol, both in March and June, suggest a PGF2 alpha-dependent estradiol synthesis, a possibility also supported by the increased plasma 17 beta-estradiol previously observed in PGF2 alpha-treated postreproductive females. The effects of captivity and castration on plasma PGF2 alpha concentrations were also studied during the annual cycle. Captivity was associated with a reduced PGF2 alpha titre, while castration did not modify prostaglandin synthesis, which may point to an extragonadal source of plasma PGF2 alpha.

Plasma prostaglandin F2 alpha in the male Triturus carnifex (Laur.) during the reproductive annual cycle and effects of exogenous prostaglandin on sex hormones

Plasma patterns of prostaglandin F2 alpha (PGF2 alpha) and sex hormones (progesterone, androgens and 17 beta-estradiol) have been studied in the male crested newt, Triturus carnifex (Laur.), during the sexual cycle. The effects of exogenous PGF2 alpha on sex steroids have also been observed. In addition, effects of one week's captivity are reported. The patterns of plasma sex hormones, during the annual cycle, are consistent with the results previously reported for the same newt species. PGF2 alpha plasma level peaks in April, is low in summer, and progressively increases during autumn to peak again in December. The April PGF2 alpha peak coincides with a plasma estradiol increase and with an androgens drop. In April-collected newts, moreover, PGF2 alpha treatment induces a significant estradiol increase. These findings lead us to suppose that at the end of the breeding season (April) a PGF2 alpha-dependent estradiol synthesis occurs which could be implied in reproductive period termination. In several vertebrates, including some amphibian species, in fact, chronic administration of estradiol results in a strong inhibition of testicular endocrine tissue activity. The putative role of PGF2 alpha-dependent estradiol production in the gonadal regulation in amphibia living in temperate zones is discussed. The autumn PGF2 alpha increase has been tentatively related to the recovery gonadal processes and secondary sexual character development.

Prostaglandin F2 alpha in female water frog, Rana esculenta: plasma levels during the annual cycle and effects of exogenous PGF2 alpha on circulating sex hormones

Prostaglandin F2 alpha (PGF2 alpha) and sex hormones (progesterone, androgens, and estradiol-17 beta) have been determined in the plasma of female water frog, Rana esculenta, utilizing radioimmunoassay methods (RIA). Plasma PGF2 alpha level increases in autumn-winter when recovery processes interest both gonad and oviduct. The PGF2 alpha plasma highest value has been recorded in October (4.52 +/- 0.58 ng/ml) and the lowest in May (1.43 +/- 0.12). The PGF2 alpha annual pattern is positively correlated to that of estradiol (but not to those of progesterone and androgens). Exogenous PGF2 alpha, injected into intact females during the various phases of the annual cycle, induces an increase of ovarian weight in frogs treated in December and February and an increase of plasma estradiol in postreproductive animals (June). Although preliminary, such results propose a putative implication of PGF2 alpha in ovarian recovery processes and in the interruption of reproductive processes in late summer.

Plasma sex hormone concentrations during the reproductive cycle in the male lizard, Podarcis s. sicula

Progesterone, 17-hydroxyprogesterone, androstenedione, 5 alpha-dihydrotestosterone, dehydroepiandrosterone, testosterone and oestradiol concentrations in the plasma were measured by simultaneous radioimmunoassay in males of the lizard Podarcis s. sicula. Hormonal determinations were performed at monthly intervals from January to December (except for August). Testosterone and androstenedione reached peak values of 174.8 ng/ml and 21.4 ng/ml in the mating season (spring) and then testosterone fell abruptly to 5.9 ng/ml in June remaining at this level during hibernation when dehydroepiandrosterone (DHA) reached a maximal level of 28.5 +/- 9.3 ng/ml. Castration resulted in a marked decrease of testosterone, androstenedione, dihydrotestosterone and DHA values, with DHA being significantly lowered only during the winter season. In castrated animals, however, testosterone and androstenedione persisted conspicuously in the plasma during the breeding period, suggesting that adrenal sex steroid output may change during the annual reproductive cycle. In intact animals, progesterone and oestradiol exhibited peak values during the refractory period after the mating season. We suggest a probable role of oestradiol in the induction of the refractory period in this lizard.

Effects of Gonadotrophin-Releasing Hormone Variants on Reproductive Organs and Plasma Testosterone in the Male Lizard, Podarcis s. sicula

Abstract The effects of various gonadotrophin-releasing hormone (GnRH) forms (mammalian GnRH (mGnRH), chicken I GnRH (cGnRH-I), chicken II GnRH (cGnRH-II) and salmon GnRH (sGnRH)) on the genital apparatus and plasma testosterone level in the male lizard, Podarcis s. sicula, have been investigated. In short duration experiments (20 min to 76 h) GnRH forms did not affect testicular and epididymal morphology. A single dose (0.05 mug) of mGnRH, cGnRH-II and sGnRH, however, induced a rise in plasma testosterone after 20 to 40 min. Variable results were obtained in the animals given GnRH variants every 12 h for 3 days since mGnRH and cGnRH-I caused a decrease of circulating hormone; cGnRH-II and sGnRH a slight increase. Daily peptide administration, for 15 to 30 days, caused severe inhibition of both testicular and epididymal activity and a significant drop of circulating testosterone. In Podarcis s. sicula, species specificity of pituitary sensitivity to GnRH variants appeared to be low. On the other hand, this gland seemed to show some desensitization after chronic peptide administration.

Estradiol-binding molecules in the hepatocytes of the female water frog, Rana esculenta, and plasma estradiol and vitellogenin levels during the reproductive cycle

Estradiol-binding molecules have been found both in cytosol and nuclear extract of hepatocytes of the female green frog Rana esculenta. These molecules show the properties of an estradiol receptor (Re): high and specific affinity for estrogens (2.10-7.10 x 10(-10) M), stability of binding at 0 and 20 degrees, localization in the nucleus, and cytosolic versus nuclear binding shift in estradiol-treated frogs. In hepatocytes, both filled and unfilled Re is detectable in all stages of the R. esculenta annual cycle. It increases during the recovery phase (September to January) when vitellogenetic processes are active in the ovary. These changes are positively correlated with vitellogenin. Only nuclear filled Re, moreover, is positively correlated to level of circulating estradiol. This suggests a direct connection: plasma estradiol level versus nuclear filled Re versus plasma vitellogenin level.

A specific nuclear protein and poly(ADPribose)transferase activity in lizard oviduct during the reproductive cycle

A specific nuclear protein (SNP) appears in the oviduct of the lizard, Podarcis s. sicula Raf., during the recovery phase of the breeding cycle. The protein has a low molecular weight (9.9 kDa), a high electrophoretic mobility and a peculiar amino acid composition. It seems to be regulated by estradiol which, in this species, is involved in oviduct stimulation. Nuclear poly(ADPribose)transferase activity increases in the oviduct as the organ grows, and it peaks upon morphological maturation. Thereafter, as the oviduct becomes secretory, the enzyme returns to basal level. A transient increase of poly(ADPribose)transferase precedes the appearance of SNP, which suggests that the two phenomena are related.

Vitellogenin hormonal control in the green frog, Pana esculenta. interplay between estradiol and pituitary hormones

1. The effect of estradiol and pituitary hormones on the titre of serum vitellogenin has been studied in Rana esculenta by rocket immunoelectrophoresis. 2. Hepatic synthesis of vitellogenin depends on physiological doses of estradiol. 3. Gonadotrophins enhance the uptake, presumably by acting directly on the oocyte plasma membrane. 4. In addition, our data support direct pituitary intervention on liver synthesis and/or release of vitellogenin. 5. Hormonal response, as evaluated by vitellogenin serum titres, tends to increase from November to July. This could be the expression of a modification, throughout the sexual cycle, of liver sensitivity to the hormones.

Plasma sex hormones and post-reproductive period in the green frog, Rana esculenta complex

The plasmatic profiles of androgens, estradiol, and progesterone, together with gonads and SSC modifications, have been followed, throughout the post-reproductive period in two Rana esculenta populations, inhabiting, respectively, a mountain pond (Colfiorito) and a sea level lagoon (Lesina). Testosterone and progesterone progressively decrease in the blood until July, while estradiol shows, in both sexes, an increase in the same month. Testosterone depletion accounts for thumb pad atrophy in the male and probably, in both sexes, for the summer interruption of sexual behavior. The estradiol increase could be linked to the induction of vitellogenin synthesis by the liver or, alternatively, could act through negative feed-back on the brain centers involved in GnRF synthesis and therefore it could be responsible for an inhibition of LH release and, in turn, of androgen synthesis/secretion by the gonads. The last function can be framed in the endocrine regulation of the so-called "refractory period" which interrupts the breeding during the summer. The hematic level of progesterone is higher during the ovulation period and this is consistent with the role assigned to the hormone, i.e., the induction of jelly release from oviductal glands. The hormonal trends in the blood of the two frog populations are very similar, although some differences exist in the levels of testosterone and progesterone.

Arginine-vasotocin and gonadal activity in the lizard, Podarcis s. sicula Raf

Arginine-vasotocine (AVT) injected into male adult lizards, Podarcis s. sicula Raf., inhibits the last phases of spermatogenesis and the endocrine activity of gonads. In female lizards the substance induces an early interruption of egg deposition.

Sex differences in liver non-specific esterases of the green frog Rana esculenta

1. Liver esterases of the green frog Rana esculenta have been fractionated on disc electrophoresis, thin-layer electrofocusing and column electrofocusing. 2. The enzyme resolves in several molecular forms some of which result sex dependent, since they disappear in castrated animals and can be induced by sex hormone administration. 3. The enzyme molecular forms which depend on female hormones might be involved in cellular modifications of hepatocytes related to yolk protein synthesis. induced by sex hormone administration. 3. The enzyme molecular forms which depend on female hormones might be involved in cellular modifications of hepatocytes related to yolk protein synthesis.

Uptake of labeled mammalian gonadotropins by ovary and oviduct of the lizard, Lacerta s. sicula, in vivo

The uptake of radioactivity by ovary, oviduct and thigh muscles of the lizard, Lacerta s. sicula, after administration of labeled mammalian gonadotropins has been followed. Ovary and oviduct show a significantly higher radioactivity than thigh muscles. The ovarian uptake, moreover, is decreased by the corresponding non-labeled gonadotropin. The meaning of these observations for the physiological regulation of reproductive processes in that lizard, are discussed.