| Summary: | 碩士 === 國立中山大學 === 生物醫學科學研究所 === 90 === Carbon monoxide (CO) has been identified as an endogenous biological messenger in the brain. Heme oxygenase (HO) catalyzes the metabolism of heme to CO and biliverdin. CO has been shown to act as a neurotransmitter and neuronal messenger in the brain. We reported recently that CO was involved in central cardiovascular regulation, modulated the baroreflex, may affect glutamatergic neurotransmission, and metabotropic glutamate receptors (mGluRs) may be coupled to the activation of HO in the nucleus tractus solitarii (NTS) of rats. We also reported previously that adenosine can increase the release of glutamate in the NTS. The present study was designed to investigate the possible interaction of CO, adenosine, and mGluRs groups in the NTS. Male Sprague-Dawley rats were anesthetized with urethane, and blood pressure were monitored intra-arterially. Unilateral microinjection of ascending doses of hemin (0.01 to 3.3 nmol), a heme molecule cleaved by HO to yield CO, produced decreases in blood pressure and heart rate dose-dependently. In addition, similar cardiovascular effects were observed in adenosine (2.3 nmol) and several agonists for mGluRs groups such as DHPG (group Ⅰ) (0.03 nmol), APDC (group Ⅱ) (0.3 nmol)and L-AP4 (group Ⅲ) (0.3 nmol). These cardiovascular effects of hemin were attenuatd by prior administration of the adenosine receptor antagonist DPSPX (0.92 nmol). Similarly, pre-treatment of HO inhibitor ZnPPⅨ or ZnDPBG (1 nmol) also attenuated the depressor and bradycadic effects of adenosine. Among the mGluRs agonists, prior administration of ZnPPⅨ (1 nmol), an inhibitor of HO activity, significantly attenuated the cardiovascular effects of APDC and L-AP4, and failed to prevent the cardiovascular responses of DHPG. These results indicated an interaction between CO and adenosine, and group Ⅱ and Ⅲ mGluRs may be coupled to the activation of HO in central cardiovascular regulation.
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