Extracellular catechol and indole turnover in the nucleus of the solitary tract of spontaneously hypertensive and Wistar-Kyoto normotensive rats in response to drug-induced changes in arterial blood pressure

Drug-induced alterations in arterial blood pressure are reflected in the extracellular fluid neurotransmitter levels of the nucleus of the solitary tract (NTS). Urethane-anesthetized spontaneously hypertensive rats (SHRs) and Wistar-Kyoto normotensive (WKY) rats were used in this study. The extracellular neurochemical profile of the NTS was quantified using the in vivo microdialysis technique. In SHR, phenylephrine-induced hypertension produced no significant changes in the extracellular norepinephrine (NE) and dihydroxyphenylacetic acid concentrations, whereas a significant increase in the serotonin metabolite 5-hydroxyindoleacetic acid (B-HIAA) concentration was observed. Wistar normotensive rats, in response to phenylephrine-induced hypertension, showed a significant increase in extracellular NE and 5-HIAA concentrations. Hypotension produced by the intravenous infusion of nitroprusside failed to show significant changes in the extracellular neurotransmitters in both SHR and WKY rats. However, there was a significant increase in B-HIAA concentration in SHRs during the rebound hypertension, which followed the nitroprusside-infused hypotension. No such change was observed in the case of the WKY rats. These results suggest the possible involvement of the serotonergic mechanisms of NTS in the regulation of normal arterial blood pressure in these two rat strains.