17ß-Estradiol Stimulates Ascorbic Acid and LHRH Release from the Medial Basal Hypothalamus in Adult Male Rats

Abstract

In the present investigation, 17ß-estradiol (E₂) and tamoxifen, an antiestrogen, were evaluated for their effects on the release of ascorbic acid (AA) and luteinizing hormone-releasing hormone (LHRH). Medial basal hypothalami (MBH) from adult male rats were incubated with graded concentrations of E₂ (10-⁹ to 10-⁶ M) or a combination of E₂ (10-⁷ M) and tamoxifen (10-⁷ and 10-⁶ M) in 0.5 ml of Krebs Ringer bicarbonate buffer for 1 hr. AA and LHRH in the incubation medium were measured by high-performance liquid chromatography and radioimmunoassay, respectively. E₂ significantly elevated both AA and LHRH release and the minimal effective dose was 10-⁷ M. A combination of E₂ (10-⁷ M) and tamoxifen (10-⁶ M) totally blocked E₂-induced AA and LHRH release. The stimulatory effect of E₂ was also suppressed in the presence of N^G-monomethyl-l-arginine, a competitive inhibitor of nitric oxide synthase (NOS), illustrating that the release is mediated by nitric oxide (NO). To further characterize the role of NO, the tissues were incubated with E₂ or a combination of E₂ + (6 anllino-5, 8-quinolinedione) LY 83583 (10-⁶ and 10-⁵ M), an inhibitor of NOS. LY 83583 was effective in suppressing E₂-induced AA and LHRH release, demonstrating that the effect was mediated by cyclic GMP. Incubation of the tissues with E₂ or a combination of E₂ + 1H-[1, 2, 4] oxadiazolo [4, 3-a] quinoxalin-1-one (O.D.Q.) (10-⁵ and 10-⁴ M), a specific inhibitor of soluble guanylyl cyclase failed to alter AA release but significantly suppressed LHRH release. The role of a prostaglandin synthesis blocker in E₂-lnduced AA and LHRH release was tested by incubating the tissues with E₂ or a combination of E₂ + Indomethacin (1.8 × 10-⁷ or 1.8 × 10-⁶ M). Indomethacin produced a significant decrease in E₂-induced AA and LHRH release, suggesting that the release process required prostaglandins as an intracellular mediator. In conclusion, E₂ stimulated both AA and LHRH release and the effect was mediated by NO and prostaglandins.