RESUMO
OMC (octyl-methoxycinnamate), an endocrine disruptor having estrogenic activity, is used in sunscreen creams as UV filter. We studied its "in vitro" effects on the hypothalamic release of Gn-RH as well as on the amino acid neurotransmitter system. OMC significantly decreased Gn-RH release in normal male and female rats as well as in castrated rats with substitutive therapy. No effects were observed in castrated rats without substitutive therapy. In males OMC increases the release of GABA, decreasing the production of glutamate (GLU) while in the female decreases the excitatory amino acid aspartate (ASP) and GLU without modifications in the hypothalamic GABA release. These results suggest that OMC acting as endocrine disruptor could alter the sex hormone-neurotransmitter-Gn-RH axis relationships in adult rats.
Assuntos
Cinamatos/farmacologia , Hormônio Liberador de Gonadotropina/metabolismo , Hipotálamo/metabolismo , Aminoácidos/metabolismo , Animais , Ácido Aspártico/metabolismo , Feminino , Hipotálamo/efeitos dos fármacos , Masculino , Ratos , Caracteres Sexuais , Protetores Solares/farmacologia , Ácido gama-Aminobutírico/metabolismoRESUMO
4-Methylbenzylidene-camphor (4-MBC), an UV-B ray filter, belongs to the endocrine disrupters involved with alterations in the reproductive axis. Our target was to study the effect of 4-MBC on the neuroendocrine parameters that regulate reproduction in prepubertal and peripubertal male rats, which received this disrupter during embryonic and fetal development. 4-MBC was administered (sc) to female rats since pregnancy onset in doses of 20, 100 and 500 mg/kg/day. The litters were sacrificed at 15 or 30 days old to determine testicular weight, gonadotropin and prolactin serum levels and also GnRH and amino acids release from the hypothalamus. The exposure to 20 mg/kg/day only increased the LH serum levels in 30-day-old males. Doses of 100 and 500 mg/kg/day caused a decrease in testicular weight and in LH, GnRH and glutamate levels, in prepubertal rats (15-day-old specimens), and an increase in, gonadotropin (LH and FSH) con-centration and aspartate levels in peripubertal rats (30-day-old specimens), without changes in testicular weight. Prolactinaemia remained unaltered in all groups. Results obtained show that the administration of high doses of 4-MBC during embryonic and fetal stage inhibits the testicular axis in male rats during the prepubertal stage and stimulates it during peripubertad stage. On the other hand in the case of low doses no significant effects were observed.
Assuntos
Cânfora/análogos & derivados , Sistema Hipotálamo-Hipofisário/efeitos dos fármacos , Hipotálamo/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal/metabolismo , Testículo/efeitos dos fármacos , Análise de Variância , Animais , Ácido Aspártico/metabolismo , Cânfora/administração & dosagem , Cromatografia Líquida de Alta Pressão , Relação Dose-Resposta a Droga , Feminino , Hormônio Foliculoestimulante/sangue , Ácido Glutâmico/metabolismo , Hormônio Liberador de Gonadotropina/metabolismo , Sistema Hipotálamo-Hipofisário/fisiologia , Hipotálamo/metabolismo , Hormônio Luteinizante/sangue , Masculino , Tamanho do Órgão , Gravidez , Prolactina/sangue , Ratos , Ratos Wistar , Protetores Solares/administração & dosagem , Testículo/crescimento & desenvolvimento , Ácido gama-Aminobutírico/metabolismoRESUMO
4-(Methylbenzylidene)-camphor (4-MBC), a UV-B ray filter, is an endocrine disruptors (ED). Our goal was to study the effect of 4-MBC on the neuroendocrine parameters that regulate reproduction in adult female and male rats that received this disrupter during prenatal development. The 4-MBC was administered (sc) to female rats (FO) since pregnancy onset, in doses of 100mg/kg every other day. The litters (F1) were sacrificed at 70 days to determine gonadotrophin serum levels and also GnRH and the amino acids glutamate, aspartate and GABA release from the hypothalamus. The male litter rats (F1) present at adult age a decrease in serum LH and FSH concentration and so also GnRH, excitatory amino acids and GABA hypothalamic secretion. The female litters (F1) rats present at adult age an increase in serum LH and FSH concentration, whereas hypothalamic GnRH release was not modified. In these animals a significant increase of hypothalamic aspartate release as well as GABA secretion decrease were observed. Glutamate secretion was not modified. All these changes were accompanied by an advance (3 days) on the vaginal opening in 4-MBC rats group. In conclusion, prenatal administration of 4-MBC disrupts the gonadal axis in a sexual dimorphic mode that could be connected with the physiological sexual differences in the development of gonadotrophin secretion hypothalamic control mechanisms.
RESUMO
OMC (octyl-methoxycinnamate), is an endocrine disruptor with estrogenic activity, which is used in sunscreen creams as a UV filter. We studied its " IN VITRO" effects on the hypothalamic release of LHRH as well as on the amino acid neurotransmitter system in immature rats of 15 (prepubertal) and 30 (peripubertal) days of age. OMC decreased the LH-RH release significantly in male and female rats of both age. In male rats OMC increased the release of GABA while in the female ones It diminished the excitatory amino acid aspartate (ASP) and Glutamate (GLU) without modifications in the hypothalamic GABA release. These results suggest that during sexual maturation the inhibitory effect of OMC on LH-RH release appears to be related to its action on the inhibitory and excitatory amino acid neurotransmitters in male and female rats.
Assuntos
Cinamatos/farmacologia , Aminoácidos Excitatórios/metabolismo , Hormônio Liberador de Gonadotropina/metabolismo , Hipotálamo/efeitos dos fármacos , Maturidade Sexual/efeitos dos fármacos , Animais , Avaliação Pré-Clínica de Medicamentos , Feminino , Hipotálamo/metabolismo , Masculino , Neurotransmissores/metabolismo , Ratos , Ratos Wistar , Caracteres Sexuais , Protetores Solares/farmacologia , Raios Ultravioleta , Ácido gama-Aminobutírico/metabolismoRESUMO
The aim of the present paper was to study the role of NO as a mediator of leptin action at the hypothalamic level during sexual maturation. First, we analyzed the effect of different leptin concentrations (10 (-13), 10 (-11) and 10 (-9) M) on Gn-RH release from anterior preoptic area and medio basal hypothalamus (APOA-MBH) of prepubertal (15 days old) and peripubertal (30 days old) female rats. Leptin 10 (-13) M was the most effective concentration in releasing Gn-RH in both groups of animals. Since glutamate (GLU) and GABA are involved in the hypothalamic control of Gn-RH neurons and also in the neuroendocrine mechanism of puberty, in a second serie of experiments, we evaluated the effect of a competitive inhibitor of nitric oxide synthase (NOS), N-monomethyl-L-arginine (NMMA) on Gn-RH, GLU and GABA release in response to leptin. Co incubation of APOA-MBH with NMMA 0.5 mM, completely blocked Gn-RH and GLU release induced by leptin 10 (-13) M in prepubertal and peripubertal rats. NMMA also blocked the stimulation of GABA release in prepubertal rats, as well as the inhibition of GABA release induced by leptin in peripubertal rats. It can be proposed that the different effect of NO on GABA release, could be related to ontogenic changes, e.g, maturation of receptors and/or interneuronal connections during sexual development. Present results provide evidence that leptin acts at the hypothalamic level to stimulate NO release, which in turn modifies the release of amino acid neurotransmitters involved in Gn-RH control.
Assuntos
Hormônio Liberador de Gonadotropina/metabolismo , Leptina/farmacologia , Óxido Nítrico Sintase/antagonistas & inibidores , Maturidade Sexual/efeitos dos fármacos , ômega-N-Metilarginina/farmacologia , Aminoácidos/metabolismo , Animais , Feminino , Óxido Nítrico/fisiologia , Óxido Nítrico Sintase/fisiologia , Ratos , Ratos WistarRESUMO
The purpose of the present study was to determine the effect of treatment with leptin on gonadotrophin secretion and hypothalamic GnRH, excitatory and inhibitory amino acids release, in prepubertal (15 days old) and peripubertal (30 days old) male rats. Rats of both ages received a single (ip) injection of 30 microg/kg leptin 60 minutes previous to sacrifice. Serum LH was determined, and the hypothalamus dissected and incubated in Earle's medium. GnRH and amino acids release were determined in the media. LH and GnRH were measured by RIA. Amino acids were assessed by HPLC-UV detection. In the two prepubertal stages, (prepubertal and peripubertal, 15 and 30 days of age respectively) leptin increased plasmatic LH levels (p < 0.01) and hypothalamic GnRH release (p < 0.01). Glutamate (GLU) release showed an increment in leptin-treated rats (p < 0.01) at both ages, while only the 30 days old rats showed an increment of the aspartate (ASP) release. GABA secretion was not modified by leptin treatment. In conclusion, the results demonstrated that leptin stimulates the LH-GnRH axis during sexual development in male rats, increasing the secretion of both hormones. The hypothalamic excitatory amino acid neurotransmitter system appears to be involved in this change.
Assuntos
Aminoácidos/metabolismo , Hormônio Liberador de Gonadotropina/metabolismo , Hipotálamo/metabolismo , Leptina/farmacologia , Hormônio Luteinizante/sangue , Maturidade Sexual/fisiologia , Animais , Ácido Aspártico/metabolismo , Cromatografia Líquida de Alta Pressão/métodos , Ácido Glutâmico/metabolismo , Hipotálamo/efeitos dos fármacos , Masculino , Radioimunoensaio , Ratos , Ácido gama-Aminobutírico/metabolismoRESUMO
The purpose of the present study was to analyse the effect of leptin treatment on the hypothalamic release of GnRH, GABA, and the excitatory amino acids (EAA), aspartate (ASP) and glutamate (GLU) involved in NMDA neurotransmission in prepubertal (15 day old) and peripubertal (30 day old) female rats. The animals were treated with a single dose of leptin (30 microg/kg i.p.) and sacrificed 60 min later. Hypothalamic samples were incubated in Earle's medium; GnRH was determined by RIA and GLU, ASP and GABA by HPLC by UV detection. The hypothalamic release of GnRH was increased by leptin at both ages, the release being significantly higher in peripubertal than in prepubertal rats. The levels of hypothalamic GABA release were different in the two groups; whereas in prepubertal rats the hypothalamic release of GABA increased with leptin administration, the neurotransmitter release decreased in the peripubertal group. On the other hand, the release of ASP was modified only in the peripubertal group, where leptin significantly increased its hypothalamic release. No modifications in leptin-induced hypothalamic release of GLU were observed at the two ages studied. In conclusion, the results showed that leptin increased GnRH release by the hypothalamus of prepubertal and peripubertal rats. In peripubertal rats this increase was accompanied by a significant decrease in the hypothalamic release of GABA as well as an enhanced release of ASP. These results and previous reports suggest that at this stage of sexual maturation, leptin exerts an stimulatory effect on GnRH by inducing release of excitatory amino acids (ASP) and reducing release of inhibitory amino acids (GABA) involved in GnRH control. In prepubertal rats the stimulating effect of the adipocyte hormone on GnRH appears to be related to its stimulative action on GABA which at this age increases GnRH release.
Assuntos
Hormônio Liberador de Gonadotropina/metabolismo , Hipotálamo/metabolismo , Leptina/farmacologia , Maturidade Sexual/fisiologia , Aminoácidos/metabolismo , Animais , Feminino , Hipotálamo/efeitos dos fármacos , Neurotransmissores/metabolismo , Ratos , Ratos Wistar , Maturidade Sexual/efeitos dos fármacosRESUMO
GABAergic, serotoninergic and excitatory amino acid systems (EAAs) regulate the prolactin (PROL) secretion in prepubertal female rats. The aim of the present paper was to determine the interrelationships of these systems on the control of this pituitary hormone. It was carried out through the following scheme: 1. The participation of the EAAs and serotonin in the effect of GABAergic system on PROL release, determined by evaluating the GABA A and GABA B receptor agonists. It was carried out on animals that were previously treated with AAEs receptor antagonist or p-chlorophenylamphetamine (PCA), this one depleting serotonin in the hypothalamus. 2. The participation of GABAergic system in the effect of serotonin and EAAs systems, determined by the evaluation of the effects of EAAs receptor agonists and of 5-HTP, a serotonin precursor. With this purpose the rats were previously treated with GABA A and GABA B receptor antagonists. 3. The interrelationships between the EAAs and the serotoninergic systems in the control of PROL secretion, determined (a) by using EAAs agonists (in rats depleted of serotonin by PCA) and (b) using EAAs antagonists (in rats treated with 5-HTP, a serotonin precursor). The administration of GABAergic agonists significantly increased PROL secretion in prepubertal female rats. Neither EAAs antagonists nor the depletion of serotonin in the brain, modified the stimulatory effects of the GABAergic system on PROL levels. This is a clear indication that the activity of the GABAergic system is independent of the serotoninergic and of the EAAs system effects on the pituitary hormone. The EAAs neurotransmitter system agonists significantly increase PROL levels. This effect was blocked by the GABAergic system antagonists but was not modified by serotonin depletion. Taking into account these facts it may be considered that the GABAergic system is involved in the stimulatory effect of EAAs on PROL secretion, this effect being independent of the serotoninergic system. 5-HTP significantly increased PROL plasma levels, and this effect was modified neither by the GABAergic nor by the EAAs receptor antagonists. These results indicate that the stimulatory effect of serotonin on PROL release is independent of the GABAergic and EAAs systems. In conclusion it may be considered that in prepubertal female rats, the GABAergic and serotoninergic systems stimulate PROL secretion by independent mechanisms that do not include EAAs. On the other hand, the effects of EAAs neurotransmission are exerted via the GABAergic system.
Assuntos
Aminoácidos Excitatórios/fisiologia , Prolactina/metabolismo , Serotonina/fisiologia , Maturidade Sexual , Ácido gama-Aminobutírico/fisiologia , 5-Hidroxitriptofano/farmacologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Animais , Maleato de Dizocilpina/farmacologia , Feminino , Antagonistas de Receptores de GABA-A , Antagonistas de Receptores de GABA-B , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Ácido Caínico/farmacologia , N-Metilaspartato/farmacologia , Ratos , Receptores de Glutamato/efeitos dos fármacos , Receptores de Glutamato/fisiologia , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , p-Cloroanfetamina/farmacologiaRESUMO
The fasting-induced gonadotropin function decrease is unspecific, because in this situation there is a lack of all nutrients. We report here the effect of specific protein lack in the diet during 21 days, on pituitary gonadotropin synthesis and response to exogenous GnRH in adult male rats. We also studied the effect of the aproteic diet (AP) on the positive feedback mechanism in adult female castrated rats. The AP diet decreased significantly, both LH and FSH pituitary concentration and also basal gonadotropin plasma levels in male rats. GnRH produced a significantly increment in LH secretion in both treated and control groups, reaching similar levels after stimulation. Nevertheless, the percentile increment from basal levels in the aproteic group was almost four times the controls, suggesting an increased sensitivity in pituitary response to GnRH in rats fed with AP diet. In female castrated rats, the aproteic diet imposed 3 weeks after the surgery was unable to reduce basal gonadotropin secretion, and so also prolactin secretion. Estradiol/progesterone (EP) administration produced the activation of positive feedback mechanism, increasing significantly LH and FSH secretion in both controls and AP groups. Nevertheless, both gonadotropin responses to EP were significantly greater in rats fed with AP diet. Basal prolactin levels and response to EP were not different between both groups. This results suggest that selective protein lack in a diet, reduced pituitary LH and FSH synthesis and secretion. This type of diet also increments pituitary sensitivity to GnRH administration in male rats, and gonadotropin response to positive feedback mechanism in female rats.
Assuntos
Proteínas Alimentares/administração & dosagem , Estradiol/farmacologia , Hormônio Foliculoestimulante/metabolismo , Hormônio Liberador de Gonadotropina/farmacologia , Hormônio Luteinizante/metabolismo , Progesterona/farmacologia , Animais , Retroalimentação , Feminino , Masculino , Ovariectomia , Adeno-Hipófise/efeitos dos fármacos , Adeno-Hipófise/metabolismo , Deficiência de Proteína/fisiopatologia , Ratos , Ratos WistarRESUMO
The present studies were designed to study the interrelationships between GABAergic, serotoninergic and excitatory amino acids systems (EAAs) in the control of gonadotropin secretion in prepubertal female rats. For this purpose we determined the effects of N-methyl-D-aspartate (NMDA), an exogenous agonist of EAAs receptors, on LH and FSH secretion in 16-day-old female rats in which the GABA-A and GABA-B receptors were blocked by bicuculline and baclofen or serotonin (5-HT) depleted by p-choloroamphetamine (PCA). In addition the effects of the GABAergic and serotoninergic systems on LH and FSH secretion were evaluated in animals treated with dibenzocycloalkenimine (diocilpine MK-801), an antagonist of NMDA neurotransmission. While muscimol, a GABA-A agonist, induced a significant increase in LH and FSH levels (P < 0.01), baclofen, a GABA-B agonist, had an inhibitory effect on these hormones (P < 0.01). MK 801, a NMDA receptor antagonist, not only suppressed the stimulatory effect of NMDA on LH and FSH but also blocked the stimulatory effect of muscimol without modifying the inhibitory action of baclofen on both gonadotropins. Bicuculline, a GABA-A receptor antagonist, did not modify the release effect of NMDA on LH and FSH. 5-HTP, a precursor of 5-HT that increases the levels of this neurotransmitter in the central nervous system significantly increased (P < 0.01) the plasma levels of LH and FSH, and this effect was blocked by the NMDA receptor antagonist MK-801. We conclude that the stimulatory effects of GABAergic and serotoninergic systems in prepubertal female rats are connected with the activation of EAA neurotransmission, while the stimulatory effects of NMDA appear to be independent of serotoninergic and GABAergic actions on LH and FSH secretion. Since both GABA and serotonin systems change their effects on LH and FSH during sexual maturation from a stimulatory action in prepubertal to an inhibitory action in adult rats and since NMDA neurotransmission has a stimulatory effect on gonadotropin secretion both in prepubertal and adult rats, it is clear that the interrelationships between GABAergic and serotoninergic systems with EAAs in the gonadotropin control are different in prepubertal and in adult rats.