title: Estrogen, but not progesterone, induces the activity of nitric oxide synthase within the medial preoptic area in female rats.
abstract: The control of gonadotropin-releasing hormone (GnRH) secretion depends on the action of ovarian steroids and several substances, including nitric oxide (NO). NO in the medial preoptic area (MPOA) stimulates the proestrus surge of luteinizing hormone (LH). We studied the effect of estrogen (Tamoxifen-TMX) and progesterone (RU-486) antagonists on mRNA and protein expression of NO synthase (NOS), the enzyme that produces NO, as well as its activity within MPOA. Female rats received s.c. injections of TMX (3mg/animal) on first and second days of the estrous cycle (9 am), RU-486 (2mg/animal) on first, second, (8 am and 5 pm) and third days of the estrous cycle (8 am) or oil (controls) and were killed on the third day (5 pm). Real time-PCR and western blotting were performed to study NOS mRNA and protein expressions. The NOS activity was indirectly assessed by measuring the conversion from [(14)C]-L-arginine into [(14)C]-L-citrulline. TMX significantly decreased neuronal NOS (nNOS) mRNA expression (90%), and the activity of NOS, but did not alter nNOS protein expression. Also, TMX significantly decreased LH, FSH, estrogen and progesterone plasma levels. RU-486 nor affected NOS mRNA and protein expressions neither the NOS activity in the MPOA, but reduced FSH levels. The nitrergic system in the MPOA can be stimulated by estrogen whereas TMX decreased NOS activity and mRNA expression. In conclusion, the involvement of the nitrergic system in the MPOA to induce the surge of LH on proestrus depends on the estrogen action to stimulate the mRNA-nNOS expression and the activity of nNOS but it does not seem to depend on progesterone action.
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil; Universidade Federal de Santa Catarina, Centro de Ciências Biológicas, Florianópolis, SC, Brazil.
authors.forename: Fernanda Barbosa
authors.initials: FB
authors.lastname: Lima
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil.
authors.forename: Fábio Honda
authors.initials: FH
authors.lastname: Ota
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil; Instituto de Ciências Biomédicas, São Paulo, SP, Brazil.
authors.forename: Fernanda Jankur
authors.initials: FJ
authors.lastname: Cabral
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil.
authors.forename: Bruno
authors.initials: B
authors.lastname: Del Bianco Borges
authors.affiliation: Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Ribeirão Preto, SP, Brazil. Electronic address: crfranci@fmrp.usp.br.
authors.forename: Celso Rodrigues
authors.initials: CR
authors.lastname: Franci
mesh_terms: D000818:Animals; D004958:Estradiol / Q000378:metabolism*; D004965:Estrogen Antagonists / Q000494:pharmacology; D030762:Estrous Cycle / Q000378:metabolism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism; D015735:Mifepristone / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D011301:Preoptic Area / Q000201:enzymology* / Q000378:metabolism; D011374:Progesterone / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013629:Tamoxifen / Q000494:pharmacology
chemical_list: D004965:Estrogen Antagonists; D013629:Tamoxifen; D015735:Mifepristone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D019001:Nitric Oxide Synthase
keywords: Estrogen; Medial preoptic area; Nitric oxide; Progesterone; RU-486; Tamoxifen