Outbreak of tularaemia in Castilla y León, Spain

In late June 2007, the Epidemiological Surveillance Network in Castilla y León, northern Spain, reported a series of cases in a rural area in the province of Palencia and in the provincial capital city of León, labelled as “fever of unknown origin”. Subsequent epidemiological investigation confirmed an outbreak of tularaemia.

Effects of systemic blockade of nitric oxide synthases on pulsatile LH, prolactin, and GH secretion in adult male rats

BACKGROUND

Nitric oxide (NO) has emerged as an important neurotransmitter involved in the control of the neuroendocrine function. NO acts at hypothalamic, pituitary, and gonadal levels. Previous data from our laboratory showed that blockade of NO generation, after systemic administration of a NO synthase inhibitor (Nomega-nitro-arginine methyl ester, NAME), increased the luteinizing hormone (LH) secretion in intact and ovariectomized females, whereas a blockade of spontaneous and steroid-induced LH and prolactin surges after NO synthase inhibition has been also described.

METHODS AND RESULTS

Adult male rats were implanted with chronic intra-auricular cannulae and 5 days later sampled at 15-min intervals during 6 h (10.00-16.00 h). Administration of NAME (40 mg/kg at 08.00 and 13.00 h) stimulated significantly (p < or = 0.01) the LH secretion, increasing LH pulse amplitude (0.58 +/- 0.14 vs. 0.08 +/- 0.01 ng/ml in controls), mean LH levels (0.64 +/- 0.15 vs. 0.15 +/- 0.03 ng/ml in controls), and area under curve (239 +/- 56 vs. 57 +/- 13 in controls). This effect was blocked by coadministration of sodium nitroprusside (SNP), a NO donor (0.5 mg/kg). The action of NAME was observed 3 h after administration, in contrast to the earlier response detected in female rats, and it appeared selective for LH, as prolactin and growth hormone secretion remained unchanged. Further analysis was carried out to determine whether the effect of NAME on the LH secretion was indirect and mediated by changes in testosterone release. To this end, adult male rats were decapitated 2 h after administration of NAME (40 mg/kg), SNP (0.5 mg/kg), or L-nitro-arginine methyl ester (L-AME), a substrate for NOS (1 g/kg). The serum testosterone concentrations were unchanged after NAME administration, but inhibited by SNP and L-AME. Finally, the effect of NAME and SNP on in vitro testosterone secretion was analyzed. NAME (10 mM) did not affect basal testosterone production, but inhibited the human chorionic gonadotropin stimulated testosterone secretion.

CONCLUSIONS

These data strongly suggest that the stimulatory effect of NAME on LH secretion is not due to an inhibition of testosterone release and is exerted at the hypothalamic-pituitary level.

Interactions between GABAergic and aminoacidergic pathways in the control of gonadotropin and GH secretion in pre-pubertal female rats

Present experiments were carried out in 23-day-old female rats to analyze the interaction between excitatory amino acids (EAAs) and gamma-aminobutyric acid (GABA) in the control of gonadotropin and GH secretion. For this purpose, serum concentrations of LH, FSH and GH were measured after injection of different agonists of EAA receptor subtypes [N-methyl-D-aspartate (NMDA); kainic acid (KA), (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)], antagonists of GABA receptors (bicuculline, phaclofen) or the combined administration of both types of drugs. The results obtained indicated that: 1) GABA has a minor physiological role in the control of LH and GH secretion, since neither LH nor GH serum concentrations changed after administration of bicuculline (antagonist of GABA(A) receptors) or phaclofen (antagonist of GABA(B) receptors); 2) GABA has a sex-specific physiological role in the control of FSH secretion in female rats, in which FSH secretion increases after phaclofen administration; 3) GH secretion was enhanced after administration of NMDA, KA and AMPA, while LH increased only after activation of NMDA receptors; 4) the stimulatory effect of NMDA on LH secretion was counteracted by administration of phaclofen; and 5) bicuculline and phaclofen reduced the ability of NMDA and AMPA to stimulate GH secretion. In conclusion, present experiments evidenced a physiological role of GABA, mediated by GABA(B) receptors, in the control of FSH secretion and a cross-talk between excitatory and inhibitory amino acids in the control of anterior pituitary secretion.

Novel expression and functional role of ghrelin in rat testis

Ghrelin, the endogenous ligand for the GH-secretagogue receptor (GHS-R), is a recently cloned peptide, primarily expressed in the stomach and hypothalamus, that acts at central levels to elicit GH release and, notably, to regulate food intake. However, the possibility of additional, as yet unknown, peripheral effects of ghrelin cannot be ruled out. In the present communication, we provide evidence for the novel expression of ghrelin and its functional receptor in rat testis. Testicular ghrelin gene expression was demonstrated throughout postnatal development, and ghrelin protein was detected in Leydig cells from adult testis specimens. Accordingly, ghrelin mRNA signal became undetectable in rat testis following selective Leydig cell elimination. In addition, testicular expression of the gene encoding the cognate ghrelin receptor was observed from the infantile period to adulthood, with the GHS-R mRNA being persistently expressed after selective withdrawal of mature Leydig cells. From a functional standpoint, ghrelin, in a dose-dependent manner, induced an average 30% inhibition of human CG- and cAMP-stimulated T secretion in vitro. This inhibitory effect was associated with significant decreases in human CG-stimulated expression levels of the mRNAs encoding steroid acute regulatory protein, and P450 cholesterol side-chain cleavage, 3beta-hydroxy steroid dehydrogenase, and 17beta-hydroxy steroid dehydrogenase type III enzymes. Overall, our data are the first to provide evidence for a possible direct action of ghrelin in the control of testicular function. Furthermore, the present results underscore an unexpected role of ghrelin as signal with ability to potentially modulate not only growth and body weight homeostasis but also reproductive function, a phenomenon also demonstrated recently for the adipocyte-derived hormone, leptin.

Differential neonatal imprinting and regulation by estrogen of estrogen receptor subtypes alpha and beta and of the truncated estrogen receptor product (TERP-1) mRNA expression in the male rat pituitary

Two distinct nuclear estrogen receptors (ERs) have been identified, the classical one, renamed ERalpha, and the more recently cloned ERbeta. In a variety of tissues, gene expression of both receptor subtypes results in the generation of multiple transcripts encoding the full-length as well as several alternately spliced isoforms. In the rat pituitary, a truncated, tissue-specific variant of ERalpha, called TERP-1, has been identified and found able to modulate ERalpha and ERbeta activity. So far, its pattern of expression and hormonal regulation have been mostly studied in females. The present study was designed to analyze the pattern of expression of TERP-1 mRNA in the male rat pituitary at different stages of postnatal development, and to evaluate the impact of neonatal imprinting and estrogen treatment upon TERP-1 expression in the male pituitary. Assessment of TERP-1 mRNA levels by semi-quantitative RT-PCR, using a variant-specific primer pair, revealed that TERP-1 is also expressed in the male rat pituitary. Relative mRNA expression levels changed markedly during postnatal development, with moderate expression of the TERP-1 transcript at birth, barely detectable levels during the infantile-prepubertal period, and maximal values in adulthood. Expression of TERP-1 was sensitive to neonatal estrogen exposure, which resulted in a significant, persistent increase in mRNA levels from the infantile period until puberty. This phenomenon was not mimicked by neonatal blockade of endogenous GnRH. In addition, estrogen was able to acutely up-regulate pituitary TERP-1 mRNA expression levels in prepubertal (30-day-old) and adult (75-day-old) males. Interestingly, neonatal imprinting as well as acute estrogen treatment resulted in opposite effects on TERP-1 and full-length ERalpha and ERbeta transcripts, the latter being decreased under both conditions. In conclusion, our data indicate that TERP-1 mRNA is expressed in a developmentally regulated manner in the male rat pituitary, and is affected by neonatal estrogen imprinting and acute estrogen treatment. Regulation of TERP-1 expression by neonatal or acute estrogen treatment may thus represent an additional tuning mechanism for estrogen actions in the male rat pituitary.

Interactions between serotoninergic and aminoacidergic pathways in the control of PRL secretion in prepubertal male rats

Prolactin secretion is controlled by the hypothalamus through different neurotransmitters which interact with multiple receptor subtypes. The discovery of different families of receptors for serotonin (5-HT1-5-HT7) and excitatory aminoacids (NMDA, KA, AMPA and metabotropic receptors) ilustrates the complexity of this regulation. Moreover, in the rat the role of different neurotransmitters changes during pubertal development. Present experiments were carried out to analyse the interactions between AMPA and serotoninergic receptors in the control of prolactin secretion in prepubertal male rats. For this purpose, 16 and 23-day old male rats were treated with 5-hydroxytryptophan (5-HTP, precursor of serotonin synthesis) plus fluoxetine (blocker of serotonin reuptake), 8-OH-DPAT (agonist of 5-HT1A receptors), DOI and alpha-Me-5-HT (agonists of 5-HT2 receptors), 1-phenylbiguanide (agonist of 5-HT3 receptors) alone or in combination with AMPA (agonist of AMPA receptors). The results obtained indicate that: (a) activation of 5-HT1A receptors stimulated PRL secretion on day 16 and inhibited it on day 23; activation of 5-HT2 receptors stimulated PRL secretion on days 16 and 23, whereas activation of 5-HT3 receptors inhibited PRL release only on day 23; (b) activation of AMPA receptors inhibited PRL secretion on day 23, but not on day 16 and (c) a cross-talk is apparent between 5-HT2 and AMPA receptors in the regulation of PRL secretion, the stimulatory effect of DOI being blocked by AMPA.

Oestrogenic effects of neonatal administration of raloxifene on hypothalamic-pituitary-gonadal axis in male and female rats

Selective oestrogen receptor modulators constitute a family of drugs that are used increasingly in the management of oestrogen-associated pathology. Raloxifene is a selective oestrogen receptor modulator that is used to treat and prevent osteoporosis in post-menopausal women. The actions of raloxifene on bone, breast, uterus and serum cholesterol concentrations have been widely analysed, but very few studies have investigated the possible actions of this drug on the central nervous system. The central nervous system of the newborn rat is very sensitive to oestrogen action. In this study a series of experiments was conducted to analyse the effects of different doses of raloxifene (50, 100, 250 or 500 microg per rat per day) administered to neonatal rats on days 1-5 of age. Female rats treated with raloxifene showed decreased gonadotrophin secretion, hyperprolactinaemia, advanced vaginal opening, decreased body weight, persistent presence of cornified epithelial cells in vaginal smears, anovulation, inhibition of positive feedback between oestradiol and LH, and infertility. Male rats showed delayed balanopreputial separation, reduced body weight and hyperprolactinaemia. All these changes resemble those obtained after neonatal administration of oestradiol benzoate, thus indicating, for the first time, that raloxifene exerts an oestrogenic action on the hypothalamic-pituitary structures controlling reproductive function in rats.

Molecular mechanisms of leptin action in adult rat testis: potential targets for leptin-induced inhibition of steroidogenesis and pattern of leptin receptor messenger ribonucleic acid expression

Leptin, the product of the ob gene, is a pivotal signal in the regulation of neuroendocrine function and fertility. Although much of the action of leptin in the control of the reproductive axis is exerted at the hypothalamic level, some direct effects of leptin on male and female gonads have also been reported. Indeed, recent evidence demonstrated that leptin is able to inhibit testosterone secretion at the testicular level. However, the molecular mechanisms behind this effect remain unclear. The focus of this study was twofold: (1) to identify potential targets for leptin-induced inhibition of steroidogenesis, and (2) to characterize in detail the pattern of expression and cellular distribution of leptin receptor (Ob-R) mRNA in adult rat testis. In pursuit of the first goal, slices of testicular tissue from adult rats were incubated with increasing concentrations of recombinant leptin (10(-9)--10(-7 )M) in the presence of human chorionic gonadotropin (hCG; 10 IU/ml). In this setting, testosterone secretion in vitro was monitored, and expression levels of mRNAs encoding steroidogenic factor 1 (SF-1), steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage enzyme (P450 scc) and 17 beta-hydroxysteroid dehydrogenase type III (17 beta-HSD) were assessed by Northern hybridization. In pursuit of the second goal, the pattern of cellular expression of the Ob-R gene in adult rat testis was evaluated by in situ hybridization using a riboprobe complementary to all Ob-R isoforms. In addition, testicular expression levels of the different Ob-R isoforms, previously identified in the hypothalamus, were analyzed by means of semi-quantitative RT-PCR. In keeping with our previous data, recombinant leptin significantly inhibited hCG-stimulated testosterone secretion. In this context, leptin, in a dose-dependent manner, was able to co-ordinately decrease the hCG-stimulated expression levels of SF-1, StAR and P450 scc mRNAs, but it did not affect those of 17 beta-HSD type III. In situ hybridization analysis showed a scattered pattern of cellular expression of the Ob-R gene within the adult rat testis, including Leydig and Sertoli cells. In addition, assessment of the pattern of expression of Ob-R subtypes revealed that the long Ob-Rb isoform was abundantly expressed in adult rat testis. However, variable levels of expression of Ob-Ra, Ob-Re, and Ob-Rf mRNAs were also detected, whereas those of the Ob-Rc variant were nearly negligible. In conclusion, our results indicate that decreased expression of mRNAs encoding several up-stream elements in the steroidogenic pathway may contribute, at least partially, to leptin-induced inhibition of testicular steroidogenesis. In addition, our data on the pattern of testicular expression of Ob-R isoforms and cellular distribution of Ob-R mRNA may help to further elucidate the molecular mechanisms of leptin action in rat testis.

Developmental and hormonal regulation of leptin receptor (Ob-R) messenger ribonucleic acid expression in rat testis

In target tissues, leptin receptor (Ob-R) gene expression results in an array of alternatively spliced isoforms (Ob-Ra to Ob-Rf) with different functional features. Recent evidence has pointed to a direct role of leptin in the control of testicular function. However, complete elucidation of the pattern of Ob-R gene expression in the male gonad is still pending. The focus of this study was to characterize in detail the developmental pattern of expression and hormonal regulation of Ob-R gene in rat testis. To this end, the overall expression of Ob-R mRNA was compared to that of the fully functional, long Ob-Rb isoform in different experimental settings, using semiquantitative reverse transcription-polymerase chain reaction. Expression of Ob-R mRNA was detected in testes from 15-, 30-, 45-, and 75-day-old rats at rather constant relative levels. In contrast, testicular expression of Ob-Rb mRNA was higher in pubertal testes (15- to 30-day-old rats) and declined in adulthood. In testes from 30-day-old animals, analysis of isoform distribution revealed that, in addition to abundant Ob-Rb mRNA levels, expression of Ob-Ra, Ob-Rf, and, to a lesser extent, Ob-Rc and Ob-Re messages is detected. Testicular Ob-R mRNA expression appeared sensitive to neonatal imprinting as neonatal treatment with estradiol benzoate (500 microg/rat; Day 1 postpartum) resulted in a persistent increase (P: < 0.01) in the relative expression level of Ob-R mRNA, a phenomenon only partially mimicked by neonatal suppression of serum gonadotropins by means of LHRH-antagonist administration. In addition, neonatal estrogenization differentially altered the pattern of expression of Ob-R isoforms in adult rat testis, as expression of Ob-Rb mRNA was decreased to undetectable levels, whereas that of Ob-Rc remained unaltered, and Ob-Ra, Ob-Rf, and, to a lesser extent, Ob-Re mRNA levels were significantly increased (P: < 0.01) by neonatal exposure to estrogen. Finally, down-regulation of testicular Ob-R gene expression by homologous and heterologous signals was demonstrated as relative levels of Ob-R and Ob-Rb mRNAs were significantly decreased (P: < 0.01), in a coordinate manner, in rat testis after exposure to human recombinant leptin in vitro, and after stimulation with hCG and FSH in vivo. In conclusion, our results indicate that testicular Ob-R gene expression is developmentally regulated, imprinted by the neonatal endocrine milieu, and sensitive to regulation by leptin and gonadotropins. The ability of pivotal signals in testicular function to regulate Ob-R gene expression further supports the contention of a direct role of leptin in functional control of the rat testis.

Neonatal imprinting and regulation of estrogen receptor alpha and beta mRNA expression by estrogen in the pituitary and hypothalamus of the male rat

In male rodents, complete reproductive function is critically dependent on adequate estrogen action at different levels of the hypothalamic-pituitary-testicular axis. However, administration of high doses of estrogen during the critical period of neonatal differentiation results in multiple defects in the reproductive axis that disrupt male fertility, the molecular mechanism(s) behind such a phenotype remaining poorly characterized. The aim of this study was twofold: (1) to characterize the effects of neonatal estrogenization upon the pattern of estrogen receptors ERalpha and ERbeta mRNA expression in the pituitary and hypothalamus of the male rat, and (2) to evaluate the ability of estrogen to acutely regulate pituitary and hypothalamic ERalpha and ERbeta mRNA expression in the male rat. To achieve the first goal, groups of male rats were treated on the first day of life with estradiol benzoate (EB; 500 microg/rat), and pituitary and hypothalamic expression of ERalpha and ERbeta mRNA levels were assayed by semiquantitative RT-PCR at different ages from the neonatal period until adulthood (days 1-75 of life). In addition, the mechanism(s) of altered pituitary expression of ERalpha and ERbeta messages in neonatally estrogenized rats was explored by comparison of the effects of neonatal treatment with estrogen or a potent gonadotropin-releasing hormone (GnRH) antagonist. For the second goal, the acute effects of a single dose of EB (12.5-25 microg/rat) on hypothalamic and pituitary ERalpha and ERbeta mRNA expression were assessed in prepubertal and adult male rats. Neonatal estrogenization permanently decreased pituitary ERalpha and ERbeta mRNA expression levels respective to control values at all ages studied. This pattern of response was similar to the short-term effects of neonatal blockade of endogenous GnRH actions. In contrast, neonatal exposure to estrogen transiently increased the hypothalamic expression levels of ERalpha and ERbeta messages. This effect was detected in neonatal (5-day-old), infantile (15-day-old) and prepubertal (30-day-old) rats, and it disappeared at puberty. In addition, estrogen was able to acutely regulate mRNA expression levels of its cognate receptor subtypes in the pituitary and hypothalamus of intact male rats. In adult (75-day-old) males, EB administration (25 microg/rat) induced a significant time-dependent decrease in pituitary ERalpha and ERbeta mRNA levels. In contrast hypothalamic expression of ERalpha and ERbeta messages was increased after acute exposure to EB (12.5 microg/rat) in prepubertal males (30 days old); yet differences in the time course of the response to estrogen were noticed between targets. In conclusion, our data indicate that estrogen is able to neonatally imprint and acutely regulate mRNA expression levels of ERalpha and ERbeta in the pituitary and hypothalamus of the male rat. Regulation of pituitary and hypothalamic ERalpha and ERbeta gene expression by the cognate ligand represents a novel mechanism whereby estrogen modulates its own biological actions upon different levels of the male reproductive axis throughout the life span.

Homologous and heterologous down-regulation of leptin receptor messenger ribonucleic acid in rat adrenal gland

Leptin, the adipocyte-produced hormone that plays a key role in body weight homeostasis, has recently been found to be involved in the regulation of the hypothalamic-pituitary-adrenal axis. Moreover, reciprocal interactions between leptin and glucocorticoids have been described. In the present communication, two different strategies were undertaken to explore the mode of action of leptin in the direct control of rat adrenal function. First, a synthetic peptide approach demonstrated that the inhibitory effect of leptin on basal and ACTH-stimulated corticosterone secretion in vitro is, at least partially, mapped to a domain of the native protein between amino acids 116 and 130, i.e. an area of the molecule also relevant in terms of regulation of food intake and endocrine control. Secondly, semi-quantitative RT-PCR analysis indicated a complex pattern of adrenal leptin receptor (Ob-R) mRNA expression, with predominant expression of the Ob-Ra and Ob-Rb isoforms, as well as moderate levels of the Ob-Rc and Ob-Rf variants, whereas negligible signals for the Ob-Re isoform were detected. Interestingly, such an expression pattern appeared hormonally regulated as exposure to human recombinant leptin (10(-7 )M) or ACTH (10(-7 )M) significantly decreased Ob-R isoform mRNA expression. Indeed, dose-dependent ligand-induced Ob-Ra and Ob-Rb mRNA down-regulation was further confirmed by adrenal stimulation with increasing concentrations (10(-9)-10(-5 )M) of the active leptin fragment, leptin 116-130 amide. Overall, our results provide evidence for a novel regulatory step at the level of Ob-R mRNA expression in the interplay between ACTH and leptin for the tuning of rat adrenal corticosterone secretion. Furthermore, our data showing down-regulation of Ob-R mRNA expression by its cognate ligand may well be relevant to leptin physiology and its alteration in various disease states.

Regulation of prolactin secretion by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in male rats

The secretion of PRL is controlled by different hypothalamic signals. Depending on the experimental model, PRL secretion increases or decreases after activation of N-methyl-d -aspartic acid and kainate receptors. Recently we have described that activation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors inhibits PRL secretion in prepubertal male rats. The aim of present study was to examine (1) the physiological relevance of this finding, (2) the possible age-related changes observed after activation or blockade of AMPA receptors, (3) the specificity of the AMPA effect, (4) the hypothalamic and/or pituitary localization of AMPA action, and (5) the mechanism(s) of action of AMPA agonists. In a first set of experiments, neonatal males (5 and 10 days old) and prepubertal (23 days old) male rats were injected with AMPA (1, 2.5 or 5 mg/kg) or the antagonist of AMPA receptors 1,2,3, 4-tetrahydro-6-nitro-2,3-dioxo-! benzo (f) quinoxaline-7-sulfonamide (NBQX; 0.25 or 0.50 mg/kg). Serum PRL concentrations decreased significantly 15 and 30 min after i.p. administration of AMPA in prepubertal male rats, while the inhibitory effect of AMPA was not observed in 5- and 10-day-old males. The effect of AMPA was abolished by NBQX but not by MK-801 (a selective antagonist of NMDA receptors). NBQX alone (0.25 or 0.50 mg/kg) had no effect on PRL release. In vitro, AMPA slightly stimulated PRL secretion by hemipituitaries from prepubertal males, suggesting that the hypothalamus is likely the site of action for the reported inhibitory action of AMPA on PRL release. In this sense, the blockade of AMPA effects in animals pretreated with domperidone (a dopaminergic antagonist) or alpha-methyl-p-tyrosine (an inhibitor of dopamine synthesis) suggests that an increase in the release of hypothalamic dopamine is probably the mechanism i! nvolved in the effect of AMPA. In a second set of experiments, the effects of AMPA (2.5 mg/kg i.p.) and NBQX (0.5 mg/kg i.p. and 20 or 40 nmol i.c.v.) were tested in freely moving adult male rats sampled during periods of 2, 3 or 6 h. In contrast with data obtained in prepubertal rats, neither AMPA nor NBQX affected PRL secretion. In conclusion, these data indicate that activation of AMPA receptors inhibits PRL secretion in prepubertal male rats. This effect probably involves the release of dopamine from the hypothalamus and disappears in adulthood.

Regulation of growth hormone (GH) secretion by different glutamate receptor subtypes in the rat

It has been firmly established that excitatory amino acids (EAAs), such as glutamate, are pivotal elements in the hypothalamic circuitry involved in the control of pituitary function. The actions of EAAs are mediated by different postsynaptic receptor subtypes, which include N-methyl D-aspartate (NMDA), kainate (KA), 2-amino-3-hydroxy-5 methyl-4-isoxazol propionic acid (AMPA) and metabotropic receptors. In this review, we summarize our experimental work on the role of EAA neurotransmission in the control of GH secretion in the rat. Detailed characterization of the effects of agonists and antagonists of glutamate receptors on GH release revealed that activation of NMDA, KA and AMPA receptors at different age-points resulted in clear-cut stimulation of GH secretion, although age- and sex-dependent differences were detected in the pattern of response to the different agonists. This stimulatory action was proven nitric oxide (NO)-dependent and not exerted at the pituitary level. In addition, evaluation of the role of hypothalamic GH-releasing hormone (GHRH) in the stimulatory action of NMDA by means of immunoneutralization of endogenous GHRH or destruction of GHRH producing neurons suggested the involvement of signals other than GHRH in this response. Further, evidence was obtained on the modulation of the EAA system by gonadal factors, and on the physiological relevance of EAA pathways in the regulation of pulsatile GH release. In conclusion, our data using the rat as animal model provide evidence for a pivotal role of glutamate pathways in the regulation of GH secretion throughout the life-span.

Neonatal exposure to estrogen differentially alters estrogen receptor alpha and beta mRNA expression in rat testis during postnatal development

The biological actions of estrogens on target cells are mediated by two nuclear receptors: the estrogen receptor (ER) alpha and the recently characterized ER beta. In the male rat, the physiological role of estrogens involves multiple actions, from masculinization of brain areas related to reproductive function and sexual behavior to regulation of testicular development and function. Paradoxically, however, administration of high doses of estrogen during the critical period of neonatal differentiation results in an array of defects in the reproductive axis that permanently disrupt male fertility. The focus of this study was to characterize the effects and mechanism(s) of action of neonatal estrogenization on the pattern of testicular ER alpha and beta gene expression during postnatal development. To this end, groups of male rats were treated at day 1 of age with estradiol benzoate (500 microg/rat), and testicular ER alpha and ER beta mRNA levels were assayed by semi-quantitative RT-PCR from the neonatal period until puberty (days 1-45 of age). Furthermore, the expression of androgen receptor (AR) mRNA was evaluated, given the partially overlapping pattern of tissue distribution of ER alpha, ER beta and AR messages in the developing rat testis. In addition, potential mechanisms for neonatal estrogen action were explored. Thus, to discriminate between direct effects and indirect actions through estrogen-induced suppression of serum gonadotropins, the effects of neonatal estrogenization were compared with those induced by blockade of gonadotropin secretion with a potent LHRH antagonist in the neonatal period. Our results indicate that neonatal exposure to estrogen differentially alters testicular expression of alpha and beta ER messages: ER alpha mRNA levels, as well as those of AR, were significantly decreased, whereas relative and total expression levels of ER beta mRNA increased during postnatal/prepubertal development after neonatal estrogen exposure, a phenomenon that was not mimicked by LHRH antagonist treatment. It is concluded that the effect of estrogen on the expression levels of ER alpha and beta mRNAs probably involves a direct action on the developing testis, and cannot be attributed to estrogen-induced suppression of gonadotropin secretion during the neonatal period.

In vitro pituitary and testicular effects of the leptin-related synthetic peptide leptin(116-130) amide involve actions both similar to and distinct from those of the native leptin molecule in the adult rat

The obese gene (ob) product, leptin, has recently emerged as a key element in body weight homeostasis, neuroendocrine function and fertility. Identification of biologically active, readily synthesized fragments of the leptin molecule has drawn considerable attention, as they may provide a powerful tool for detailed characterization of the biological actions of leptin in different experimental settings. Recently, a fragment of mouse leptin protein comprising amino acids 116-130, termed leptin(116-130) amide, was shown to mimic the effects of the native molecule in terms of body weight gain and food intake, and to elicit LH and prolactin (PRL) secretion in vivo. As a continuation of our previous experimental work, the present study reports on the effects of leptin(116-130) amide on basal and stimulated testosterone secretion by adult rat testis in vitro. In addition, a comparison of the effects of human recombinant leptin and leptin(116-130) amide at the pituitary level on the patterns of LH, FSH, PRL and GH secretion is presented. As reported previously by our group, human recombinant leptin(10(-9)-10(-7)M) significantly inhibited both basal and human chorionic gonadotrophin (hCG)-stimulated testosterone secretion in vitro. Similarly, incubation of testicular tissue in the presence of increasing concentrations of leptin(116-130) amide (10(-9)-10(-5)M) resulted in a dose-dependent inhibition of basal and hCG-stimulated testosterone secretion; a reduction that was significant from a dose of 10(-7)M upwards. In addition, leptin(116-130) amide, at all doses tested (10(-9)-10(-5)M), significantly decreased LH and FSH secretion by incubated hemi-pituitaries from adult male rats. In contrast, in the same experimental protocol, recombinant leptin(10(-9)-10(-7)M) was ineffective in modulating LH and FSH release. Finally, neither recombinant leptin nor leptin(116-130) amide were able to change basal PRL and GH secretion in vitro. Our results confirm the ability of leptin, acting at the testicular level, to inhibit testosterone secretion, and map the effect to a domain of the leptin molecule that lies between amino acid residues 116 and 130. In addition, we provide evidence for a direct inhibitory action of leptin(116-130) amide on pituitary LH and FSH secretion, a phenomenon not observed for the native leptin molecule, in the adult male rat.

Role of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in the control of prolactin, growth hormone and gonadotropin secretion in prepubertal rats

Excitatory amino acids, such as glutamate, constitute a major transmitter system in the control of hypothalamic-pituitary secretion. Different subtypes of glutamate receptors, such as NMDA (N-methyl-d-aspartic acid) and KA (kainate) receptors, are involved in the control of anterior pituitary secretion. Other receptor subtypes, such as AMPA (activated by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) and metabotropic receptors, have been identified, although their role in the control of neuroendocrine function remains largely unknown. Recent reports have demonstrated the involvement of AMPA receptors in the control of the steroid-induced luteinizing hormone (LH) surge in female and growth hormone (GH) secretion in male rats. The aim of this study was to assess the potential role of AMPA receptors in the control of GH, prolactin (PRL), LH and follicle-stimulating hormone (FSH) secretion in prepubertal 23-day-old rats. To this end, prepubertal female rats were injected with AMPA (2.5 or 5 mg/kg i.p.) or the antagonist of AMPA receptors 1,2,3,4-tetrahydro-6-nitro-2, 3-dioxo-benzo (f) quinoxaline-7-sulfonamide (NBQX; 0.25 or 0.50 mg/kg i.p.). Serum LH and FSH concentrations and hypothalamic LH-releasing hormone (LHRH) content remained unchanged after AMPA or NBQX administration. In contrast, serum PRL levels significantly decreased 15, 30 and 60 min after i.p. administration of AMPA and increased 120 min after NBQX treatment, whereas serum GH levels increased after AMPA treatment and decreased after NBQX administration. Considering that AMPA has been shown to activate a subset of kainate receptors, its effects were compared with those elicited by 2.5 mg/kg KA in prepubertal female rats. At this age, however, KA was unable to reproduce the effects of AMPA on PRL and GH secretion, thus suggesting that the actions observed after AMPA administration were carried out specifically through AMPA receptors. In addition, as the effects of AMPA on LH secretion in adult females have been proved to be steroid-dependent, the effects of AMPA (2.5 mg/kg) and NBQX (0.5 mg/kg) were tested in prepubertal animals with different gonadal backgrounds, i.e. intact males, and intact and ovariectomized (OVX) females. The effects of AMPA in prepubertal females appeared to be modulated by ovarian secretion, as the inhibition of PRL secretion disappeared and LH secretion was partially suppressed by AMPA in OVX animals whereas the stimulatory effect on GH release was enhanced by ovariectomy. Furthermore, in male rats, AMPA administration significantly decreased PRL secretion and increased serum GH levels, the amplitude of the GH response being higher than in prepubertal females. To ascertain the pituitary component for the reported actions of AMPA, hemi-pituitaries of male rats were incubated in the presence of AMPA (10(-8)-10(-6) M). The results obtained showed no effect of AMPA on PRL, GH and gonadotropin secretion in vitro. Finally, we investigated the involvement of the dopaminergic (DA) system in the inhibitory action of AMPA on PRL secretion. Pre-treatment of prepubertal female rats with a dopamine receptor antagonist (domperidone: 1 mg/kg) resulted in the blockage of AMPA-mediated inhibition of PRL secretion, thus suggesting that this action is probably mediated by an increase in DA activity. In conclusion, we provide evidence for the physiological role of AMPA receptors in the control of PRL and GH secretion in prepubertal rats. In contrast, our data cast doubts on the involvement of AMPA receptors in the regulation of gonadotropin secretion at this age. The effects of AMPA reported herein were not mediated through activation of kainate receptors and were probably exerted at the hypothalamic or suprahypothalamic levels. In addition, we show that ovarian secretion actively modulates the effects of AMPA receptor activation on anterior pituitary secretion in prepubertal female rats.

Leptin inhibits testosterone secretion from adult rat testis in vitro

Leptin, the product of the ob gene, has emerged recently as a pivotal signal in the regulation of fertility. Although the actions of leptin in the control of reproductive function are thought to be exerted mainly at the hypothalamic level, the potential direct effects of leptin at the pituitary and gonadal level have been poorly characterised. In the present study, we first assessed the ability of leptin to regulate testicular testosterone secretion in vitro. Secondly, we aimed to evaluate whether leptin can modulate basal gonadotrophin and prolactin (PRL) release by incubated hemi-pituitaries from fasted male rats. To attain the first goal, testicular slices from prepubertal and adult rats were incubated with increasing concentrations (10(-9)-10(-7) M) of recombinant leptin. Assuming that in vitro testicular responsiveness to leptin may be dependent on the background leptin levels, testicular tissue from both food-deprived and normally-fed animals was used. Furthermore, leptin modulation of stimulated testosterone secretion was evaluated by incubation of testicular samples with different doses of leptin in the presence of 10 IU human chorionic gonadotrophin (hCG). In addition, analysis of leptin actions on pituitary function was carried out using hemi-pituitaries from fasted adult male rats incubated in the presence of increasing concentrations (10(-9)-10(-7) M) of recombinant leptin. Serum testosterone levels, and basal and hCG-stimulated testosterone secretion by incubated testicular tissue were significantly decreased by fasting in prepubertal and adult male rats. However, a significant reduction in circulating LH levels was only evident in adult fasted rats. Doses of 10(-9)-10(-7) M leptin had no effect on basal or hCG-stimulated testosterone secretion by testes from prepubertal rats, regardless of the nutritional state of the donor animal. In contrast, leptin significantly decreased basal and hCG-induced testosterone secretion by testes from fasted and fed adult rats. In addition, 10(-9) M leptin inhibited LH and FSH secretion by incubated hemi-pituitaries from fasted adult males, whereas, at all doses tested, it was ineffective in modulating PRL release. Our results show that leptin, depending on the state of sexual maturation, is able to inhibit testosterone secretion acting at the testicular level. Furthermore, the present data suggest that the actions of leptin on the reproductive system are complex and are probably carried out at different levels of the hypothalamic-pituitary-gonadal axis.

Regulation of growth hormone secretion by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in infantile, prepubertal, and adult male rats

Excitatory amino acids, such as glutamate, constitute a major transmitter system in the control of hypothalamic-pituitary function. Different subtypes of glutamate receptors, such as N-methyl-D-aspartic acid and kainate receptors, have been involved in the control of GH secretion. Other excitatory amino acid receptor subtypes, as alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), amino-4-phosphobutyric acid, and metabotropic receptors, have been identified, yet their role in the control of neuroendocrine function remains to be completely characterized. The purpose of this study was to assess the potential involvement of AMPA receptors in the control of GH secretion. In a first set of experiments, neonatal (5 and 10 days) and prepubertal (23 days) male rats were injected with AMPA (1, 2.5, or 5 mg/kg) or the antagonist of AMPA receptors, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo(f)quinoxaline-7-sulfonamide (NBQX; 0.25 or 0.50 mg/kg). Serum GH concentrations significantly increased 15 min after i.p. administration of AMPA in both neonatal and prepubertal male rats. In addition, serum GH concentrations decreased after NBQX treatment. The stimulatory effect of AMPA was abolished by pretreatment with the blocker of nitric oxide synthase, nitro(w)-arginine-methyl ester (40 mg/kg), and was partially counteracted by the simultaneous administration of GH-releasing hormone (500 microg/kg). Moreover, AMPA was unable to elicit in vitro GH secretion by hemipituitaries from prepubertal males, pointing out that the hypothalamus is probably the site of action for the reported stimulatory action of AMPA on GH release. In a second set of experiments, the effects of AMPA and NBQX were tested in adult male rats. As in prepubertal animals, AMPA significantly increased GH secretion in adult males, whereas NBQX (20 or 40 nmol), administered through intracerebroventricular injection, induced a significant decrease in the amplitude of GH pulses. In conclusion, our data indicate that AMPA receptors have a physiological stimulatory role in the control of GH secretion in male rats throughout the life span. This effect depends on appropriate nitric oxide synthesis during the prepubertal age. In addition, AMPA receptors appear to modulate pulsatile GH secretion in adulthood.

Nitro(w)-arginine methyl ester treatment delayed the onset of puberty in female rats

It is well documented that nitric oxide (NO) stimulates LHRH, LH and GH release. Present experiments were carried out to analyse whether the blockade of NO generation can affect body growth and puberty onset in female rats. Prepubertal female rats were treated with L-nitro(w) arginine methyl ester (NAME), a blocker of nitric oxide synthase, from day 25 to first estrous (400 or 800 mg/L in drinking water). We measured body growth, age and body weight at vaginal opening and first estrous, and the ovarian and uteri weights and serum LH and FSH concentrations the day of first estrous. Females treated with NAME showed a normal body growth pattern and a delayed puberty. Serum LH concentrations were increased in groups treated with NAME. This stimulatory effect was also observed in 30 and 90 day-old females decapitated 60 min after NAME administration (40 mg/Kg i.p.). We conclude that blockade of NO generation delays puberty in female rats by mechanism(s) other than its effects on LH release.

Male sexual behavior and human papillomavirus DNA: key risk factors for cervical cancer in Spain

BACKGROUND

It is now established that certain types of human papillomaviruses (HPVs) are the sexually transmitted agents etiologically linked to cervical cancer. Studies assessing the contribution of the male's sexual behavior and genital HPV DNA status to the risk of development of cervical neoplasia in sexual partners have yielded inconsistent results.

PURPOSE

This study evaluates the role of men's sexual behavior and the presence of HPV DNA in the penis on the development of cervical cancer in their sexual partners in Spain, a low-risk area for cervical neoplasia.

METHODS

Husbands (n = 633) of women participating in two case-control studies of cervical neoplasia were interviewed to obtain information on lifestyle habits, including sexual practices. Cytologic samples were taken from the distal urethra and the surface of the glans penis of 183 husbands of case women and of 171 husbands of control women. These samples were analyzed by a polymerase chain reaction-based system using a generic probe and 25 type-specific probes for the detection and typing of HPV DNA. Serologic specimens were also obtained and analyzed for antibodies to Chlamydia trachomatis, Treponema pallidum, herpes simplex virus type II, and Neisseria gonorrhoeae.

RESULTS

The presence of HPV DNA in the husbands' penis conveyed a fivefold risk of cervical cancer to their wives (adjusted odds ratio [OR] for HPV DNA positivity = 4.9; 95% confidence interval [CI] = 1.9-12.6). The risk of cervical cancer was strongly related to HPV type (adjusted OR for HPV type 16 = 9.0; 95% CI = 1.1-77.5), to the husbands' number of extramarital partners (adjusted OR = 11.0; 95% CI = 3.0-40.0; for > or = 21 women versus one), and to the number of prostitutes as extramarital sexual partners (adjusted OR = 8.0; 95% CI = 2.9-22.2; for > or = 10 women versus none). Presence of antibodies to C. trachomatis (adjusted OR = 2.6; 95% CI = 1.4-4.6) and an early age at first sexual intercourse of the husband (adjusted OR = 3.2; 95% CI = 1.7-5.9; for < or = 15 years versus > or = 21 years) were also associated with cervical neoplasia in the wife. After adjustment for these variables and for the wife's pack-years of smoking, the husband's smoking was moderately associated with cervical cancer in his wife (adjusted OR = 2.5; 95% CI = 1.4-4.4; for > or = 26.2 pack-years versus none).

CONCLUSIONS

The study supports the role of men as vectors of the HPV types that are related to cervical cancer. Life-time number of female sexual partners, number of female prostitutes as sexual partners, and detection of HPV DNA in the penis of husbands are all surrogate markers of exposure to HPV during marriage.

IMPLICATIONS

Men who report multiple sexual partners or who are carriers of HPV DNA may be vectors of high-risk HPV types and may place their wives at high risk of developing cervical cancer. Prostitutes are an important reservoir of high-risk HPVs.

Sexually transmitted agents and cervical neoplasia in Colombia and Spain

Case-control studies of cervical intra-epithelial neoplasia grade III (CIN III) and of invasive cervical cancer were carried out in Spain and Colombia to assess the relationship between cervical cancer and 6 common sexually transmitted agents (STAs). The CIN-III studies included 525 cases and 512 controls matched for age and for the place of recruitment; the invasive-cancer studies included 373 histologically confirmed cases of squamous-cell carcinoma and 387 age-stratified controls selected randomly from the populations that generated the cases. Antibodies to Chlamydia trachomatis, Neisseria gonorrhoeae, Treponema pallidum, herpes simplex virus type II (HSV-2) and cytomegalovirus (CMV) were tested in 88% of the women. Cervical scrapes were examined for HPV DNA in 63% of the women using a polymerase-chain-reaction assay (PCR). Among controls, the highest antibody prevalence was to CMV (96.5%), followed by HSV-2 (31.4%) and C. trachomatis (23.3%). For all STAs, the sero-prevalence was markedly higher in Colombia than in Spain both for cases and for controls. After adjustment for the presence of HPV DNA, C. trachomatis was the only STA associated with CIN III in both countries; Spain and Colombia. In both countries, the risk of CIN III increased with increasing of C. trachomatis antibody titers. Among Spanish women, an increase in risk of invasive carcinoma was found for those with antibodies to N. gonorrhoeae; those with antibodies to HSV-2 and those with antibodies to C. trachomatis. These associations were present only in HPV-DNA-negative women. Among HPV-DNA-positive women, none of the STAs considered were associated with cervical neoplasia. Our findings could be interpreted as indicating that past infections with HSV-2, N. gonorrhoeae and C. trachomatis are surrogate markers of HPV, but because HPV DNA may have escaped detection, we cannot exclude that these STAs are also of separate etiological significance.

[Human papilloma virus in the etiology of cervicouterine cancer]

The objectives of this study were to confirm the hypothesis that invasive carcinoma of the uterine cervix and the precursors of that condition are most often caused by human papilloma virus (HPV) infections, and to determine whether or not other risk factors are involved in the neoplastic process. For this purpose, four concurrent case-control studies were carried out. Two included cases of invasive cervical cancer and population-based controls. The other two included cases of in situ carcinoma and controls. Research was carried out in nine provinces of Spain and in Cali, Colombia. The identification of cases took place between June 1985 and June 1988. The studies included 436 incident cases of invasive carcinoma and 387 controls, selected at random from the corresponding populations, and 525 cases of in situ carcinoma and 512 controls paired by age, place of recruitment, and date that cytological specimens were taken from the women participating in cytological screening programs. Exposure to HPV was detected through hybridization tests after amplification by polymerase chain reaction (PCR) in exfoliated cervical cells from cases and controls. Exposure to HPV was the principal risk factor in the four studies. For invasive carcinoma, the relative risk and 95% confidence interval were 46.2 (18.5-115.1) in Spain and 15.6 (6.9-34.7) in Colombia. For in situ carcinoma, the figures were 56.9 (24.8-130.6) in Spain and 15.5 (8.2-29.4) in Colombia. This strong association was specific for types 16, 18, 31, 33, and 35 as well as still-unclassified HPV types.(ABSTRACT TRUNCATED AT 250 WORDS)