Summary: | 碩士 === 國立陽明大學 === 藥理學研究所 === 103 === Hydrogen sulfide (H2S) is the third member of gasotransmitter found in central nervous system (CNS). It is reported that H2S may play an important role in central regulation of cardiovascular function. The presence of cystathionine β synthase (CBS), the major H2S-synthesizing enzyme in CNS, was found to be located in the nucleus tractus solitarii (NTS), the principal nuclei for signal integration in baroreflex circuit. However, the effect of H2S in the NTS on baroreflex response (BRR) remains to be elucidated. Our previous study found that activation of PKA-PI3K/Akt-nNOS signaling pathway in the NTS could enhance BRR. Furthermore, H2S was reported to have interaction with the molecules in the signaling pathway. Thus, the aims of the present study were to investigate the effect of H2S and evaluate the involvement of PKA-PI3K/Akt-nNOS signaling pathway on BRR regulation by H2S in the NTS.
In this study, all experiments were carried out in anesthetized Sprague-Dawley rats. The result showed that BRR was enhanced by intravenous infusion 3-6 mg/kg of sodium hydrosulfide (NaHS), a well-known H2S donor, without change in hemodynamic balance. Intra-NTS microinjection of NaHS (2-4 nmol) could enhance BRR, indicating that NTS is the site of action for enhancement of BRR by H2S. Pharmacological results showed that H2S-induced enhancement of BRR was significantly blunted by intra-NTS microinjection of PKA inhibitor (Rp-8-br-cAMP, 1 nmol), PI3K inhibitor (Wortmannin, 5 fmol), Akt inhibitor (API-2, 50 pmol) or nNOS inhibitor (NPLA, 250 pmol). Biochemical evidence further showed that the protein level of PKAβ (active form of PKA), Akt phosphorylation on Ser473 and Thr308, nNOS phosphorylation on Ser1417, and PKG-1 (active form of PKG) in the NTS were increased after administration of NaHS. Moreover, H2S-induced increase in Akt phosphorylation was significantly attenuated by pretreatment with PKA or PI3K inhibitor. H2S-induced increase in nNOS phosphorylation in the NTS was significantly blocked by pretreatment with PKA, PI3K or Akt inhibitors. Finally, inhibition of synthesis of endogenous H2S in the NTS by AOAA (20-200 pmol) did not affect BRR, but intra-NTS microinjection with S-adenosyl-l-methionine (SAM, 100 pmol), an allosteric activator of CBS, could enhance BRR.
In conclusion, these results suggest that PKA- PI3K/Akt-nNOS signaling pathway in the NTS is involved in H2S-enhanced BRR. Although no physiological and tonical production of H2S was involved in BRR regulation, activation of CBS in the NTS results in comparable enhancing effect of exogenous H2S on BRR.
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