RESUMO
Melatonin can contribute to glucose homeostasis either by decreasing gluconeogenesis or by counteracting insulin resistance in distinct models of obesity. However, the precise mechanism through which melatonin controls glucose homeostasis is not completely understood. Male Wistar rats were administered an intracerebroventricular (icv) injection of melatonin and one of following: an icv injection of a phosphatidylinositol 3-kinase (PI3K) inhibitor, an icv injection of a melatonin receptor (MT) antagonist, or an intraperitoneal (ip) injection of a muscarinic receptor antagonist. Anesthetized rats were subjected to pyruvate tolerance test to estimate in vivo glucose clearance after pyruvate load and in situ liver perfusion to assess hepatic gluconeogenesis. The hypothalamus was removed to determine Akt phosphorylation. Melatonin injections in the central nervous system suppressed hepatic gluconeogenesis and increased hypothalamic Akt phosphorylation. These effects of melatonin were suppressed either by icv injections of PI3K inhibitors and MT antagonists and by ip injection of a muscarinic receptor antagonist. We conclude that melatonin activates hypothalamus-liver communication that may contribute to circadian adjustments of gluconeogenesis. These data further suggest a physiopathological relationship between the circadian disruptions in metabolism and reduced levels of melatonin found in type 2 diabetes patients.
Assuntos
Antioxidantes/farmacologia , Gluconeogênese/efeitos dos fármacos , Hipotálamo/metabolismo , Fígado/metabolismo , Melatonina/farmacologia , Proteína Oncogênica v-akt/metabolismo , Receptor MT1 de Melatonina/efeitos dos fármacos , Receptor MT2 de Melatonina/efeitos dos fármacos , Animais , Western Blotting , Imunofluorescência , Teste de Tolerância a Glucose , Hipotálamo/efeitos dos fármacos , Injeções Intraventriculares , Fígado/efeitos dos fármacos , Masculino , Fosfatidilinositol 3-Quinases/metabolismo , Ácido Pirúvico/metabolismo , Ratos , Ratos Wistar , Receptores Muscarínicos/efeitos dos fármacosRESUMO
BACKGROUND: Melatonin is associated with direct or indirect actions upon female reproductive function. However, its effects on sex hormones and steroid receptors during ovulation are not clearly defined. This study aimed to verify whether exposure to long-term melatonin is able to cause reproductive hormonal disturbances as well as their role on sex steroid receptors in the rat ovary, oviduct and uterus during ovulation. METHODS: Twenty-four adult Wistar rats, 60 days old (+/-250 g) were randomly divided into two groups. Control group (Co): received 0.9% NaCl 0.3 mL+95% ethanol 0.04 mL as vehicle; Melatonin-treated group (MEL): received vehicle+melatonin [100 µg/100 g BW/day] both intraperitoneally during 60 days. All animals were euthanized by decapitation during the morning estrus at 4 a.m. RESULTS: Melatonin significantly reduced the plasma levels of LH and 17 beta-estradiol, while urinary 6-sulfatoximelatonin (STM) was increased at the morning estrus. In addition, melatonin promoted differential regulation of the estrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR) and melatonin receptor (MTR) along the reproductive tissues. In ovary, melatonin induced a down-regulation of ER-alpha and PRB levels. Conversely, it was observed that PRA and MT1R were up-regulated. In oviduct, AR and ER-alpha levels were down-regulated, in contrast to high expression of both PRA and PRB. Finally, the ER-beta and PRB levels were down-regulated in uterus tissue and only MT1R was up-regulated. CONCLUSIONS: We suggest that melatonin partially suppress the hypothalamus-pituitary-ovarian axis, in addition, it induces differential regulation of sex steroid receptors in the ovary, oviduct and uterus during ovulation.
Assuntos
Estradiol/sangue , Tubas Uterinas/metabolismo , Hormônio Luteinizante/sangue , Melatonina/farmacologia , Ovário/metabolismo , Receptores de Esteroides/metabolismo , Útero/metabolismo , Animais , Tubas Uterinas/efeitos dos fármacos , Feminino , Ovário/efeitos dos fármacos , Ovulação , Ratos , Ratos Wistar , Receptor MT1 de Melatonina/efeitos dos fármacos , Reprodução/efeitos dos fármacos , Útero/efeitos dos fármacosRESUMO
Background: Melatonin receptors are widely distributed in human tissues but they have not been reported in human adrenal gland. Aim: To assess if the human adrenal gland expresses melatonin receptors and if melatonin affeets cortisol response to ACTH in dexamethasone suppressed volunteers. Material and methods: Adrenal glands were obtained from 4 patients undergoing unilateral nephrectomy-adrenalectomy for renal cáncer. Expression of mRNA MT1 and MT2 melatonin receptors was measured by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The effect of melatonin on the response to intravenous (i.v.) ACTH was tested (randomized cross-over, double-blind, placebo-controlled tríal) in eight young healthy males pretreated with dexamethasone (1 mg) at 23:00 h. On the next day at 08:00 h, an i.v. Une was inserted, at 08:30 h, and after a blood sample, subjeets ingested 6 mg melatonin or placebo. At 09:00 h, 1-24 ACTH (Cortrosyn, 1µg/1.73 m² body surface área) was injected, drawing samples at 0, 15, 30, 45 and 60 minutes after. Melatonin, cortisol, cortisone, progesterone, aldosterone, DHEA-S, testosterone and prolactin were measured by immunoassay. Results: The four adrenal glands expressed only MT1 receptor mRNA. Melatonin ingestión reduced the cortisol response to ACTH from 14.6+1.45µg/dl at 60 min in the placebo group to 10.8+1.2µg/dl in the melatonin group (p <0.01 mixed model test). It did not affect other steroid hormone levels and abolished the morningphysiological decline of prolactin. Conclusions: The expression ofMTl melatonin receptor in the human adrenal, and the melatonin reduction of ACTH-stimulated cortisol production suggest a direct melatonin action on the adrenal gland .
Assuntos
Adulto , Humanos , Masculino , Adulto Jovem , Glândulas Suprarrenais/efeitos dos fármacos , Hormônio Adrenocorticotrópico/farmacologia , Hidrocortisona/biossíntese , Melatonina/farmacologia , Receptor MT1 de Melatonina/análise , /análise , Glândulas Suprarrenais , Hormônio Adrenocorticotrópico/administração & dosagem , Estudos Cross-Over , Dexametasona/farmacologia , Método Duplo-Cego , Glucocorticoides/farmacologia , Imunoensaio , Melatonina/administração & dosagem , RNA Mensageiro/análise , Receptor MT1 de Melatonina/efeitos dos fármacos , /efeitos dos fármacos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de Tempo , Adulto JovemRESUMO
BACKGROUND: Melatonin receptors are widely distributed in human tissues but they have not been reported in human adrenal gland. AIM: To assess if the human adrenal gland expresses melatonin receptors and if melatonin affects cortisol response to ACTH in dexamethasone suppressed volunteers. MATERIAL AND METHODS: Adrenal glands were obtained from 4 patients undergoing unilateral nephrectomy-adrenalectomy for renal cancer. Expression of mRNA MT1 and MT2 melatonin receptors was measured by Reverse TranscriPtase Polymerase Chain Reaction (RT-PCR). The effect of melatonin on the response to intravenous (i.v.) ACTH was tested (randomized cross-over, double-blind, placebo-controlled trial) in eight young healthy males pretreated with dexamethasone (1 mg) at 23:00 h. On the next day, at 08:00 h, an i.v. line was inserted, at 08:30 h, and after a blood sample, subjects ingested 6 mg melatonin or placebo. At 09:00 h, 1-24 ACTH (Cortrosyn, 1 microg/1.73 m2 body surface area) was injected, drawing samples at 0, 15, 30, 45 and 60 minutes after. Melatonin, cortisol, cortisone, progesterone, aldosterone, DHEA-S, testosterone and prolactin were measured by immunoassay. RESULTS: The four adrenal glands expressed only MT1 receptor mRNA. Melatonin ingestion reduced the cortisol response to ACTH from 14.6 +/- 1.45 microg/dl at 60 min in the placebo group to 10.8 +/- 1.2 microg/dl in the melatonin group (p < 0.01 mixed model test). It did not affect other steroid hormone levels and abolished the morning physiological decline of prolactin. CONCLUSIONS: The expression of MT1 melatonin receptor in the human adrenal, and the melatonin reduction of ACTH-stimulated cortisol production suggest a direct melatonin action on the adrenal gland.
Assuntos
Glândulas Suprarrenais/efeitos dos fármacos , Hormônio Adrenocorticotrópico/farmacologia , Hidrocortisona/biossíntese , Melatonina/farmacologia , Receptor MT1 de Melatonina/análise , Receptor MT2 de Melatonina/análise , Glândulas Suprarrenais/metabolismo , Hormônio Adrenocorticotrópico/administração & dosagem , Adulto , Estudos Cross-Over , Dexametasona/farmacologia , Método Duplo-Cego , Glucocorticoides/farmacologia , Humanos , Imunoensaio , Masculino , Melatonina/administração & dosagem , RNA Mensageiro/análise , Receptor MT1 de Melatonina/efeitos dos fármacos , Receptor MT2 de Melatonina/efeitos dos fármacos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de Tempo , Adulto JovemRESUMO
Melatonin, a derivative of tryptophan that is present in all vertebrates, was first described in bovine pineal gland. It is known that melatonin is a highly conserved molecule, present also in unicellular organisms and plants. Several effects of melatonin have been described, including receptor- and non-receptor-mediated actions. Herein, we studied the effects of melatonin on in vitro and in vivo cell proliferation of Cloudman S-91 murine melanoma cells. We demonstrated that melatonin treatment significantly inhibits S-91 melanoma cell proliferation in vitro (EC50 = 10-7 m) as well as reduces tumor growth in vivo. We also demonstrated that melatonin directly increases the activity of the antioxidant enzymes catalase and glutathione peroxidase. These effects are most likely triggered through the direct intracellular action of melatonin, since the presence of receptors could not be demonstrated in this cell line. Expression of MT-1 melatonin receptor by stable transfection, mediated a dramatic antiproliferative melatonin effect (EC50 = 10-10 m) in S-91 cells. The expressed receptor is negatively coupled to the adenylyl cyclase/cyclic AMP signaling pathway via Gi protein. These results suggest that expression of the MT-1 melatonin receptor in melanoma cells is a potential alternative approach to specifically target cells in cancer therapeutic treatment.