Numerical analysis of cumulative impact of phytoplankton photoresponses to light variation on carbon assimilation.

Light variation in temporal and spatial domains is a key constraint on the photosynthetic performance of phytoplankton. The most obvious responses are the modification of cell pigment content either to improve photocapture or to mitigate photo-damage. Very few studies have analyzed whether light variation significantly alters carbon assimilation, especially in a fluctuating light environment as in the mixed layer of the ocean. We addressed the question using a modeling approach, which allows the reproduction of most of the possible scenarios, obtained with great difficulty from laboratory or field experiments. The complete model is based on the dynamic coupling of a photoacclimation and photodamage-repair responses. In this combined model the virtual phytoplankton is exposed to different light regimes (steady, square wave, sinusoidal light-dark cycles and fluctuating regimes). The results reconcile controversial results on different photoacclimation states achieved during fluctuating light regimes. The model produces a depression of carbon assimilation in any light fluctuating scenario, as compared to steady light regimes, due to the temporal delay between light fluctuations and photoresponses. These results suggest the possibility of selective pressure during evolution, more effective on photoprotective mechanisms than on optimization of light harvesting.

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.

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.

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.

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-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.

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.

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.

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.

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.

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.

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.