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Effects of chronic captopril treatment on the electrical-microstimulation-induced blood pressure changes and electrophysiological properties of cardiovascular neurons in the rostral ventrolateral medulla of the spontaneously hypertensive rat.

The effects of chronic treatment with captopril, an angiotensin-converting enzyme inhibitor, on various properties of the rostral ventrolateral medulla (RVL) were studied in spontaneous hypertensive rats (SHR) given captopril (orally at a dose of 30 mg/kg) or vehicle from the age of 4-5 weeks to 19-20 weeks. In SHR, such a treatment with captopril resulted in an arterial blood pressure similar to that of normotensive Wistar Kyoto rats (WKY). Upon electrical microstimulation of the RVL, the minimal threshold current required to elicit a pressor response in captopril-treated SHR was significantly higher than that observed in SHR. Furthermore, analysis of the discharge pattern of RVL spinal projecting cardiovascular neurons showed a significant difference between captopril-treated and untreated SHR with respect to the proportion of double discharge units and the regularity of single discharge units. These properties of the RVL in captopril-treated SHR were, however, similar to those of WKY. Upon withdrawal of electrical microstimulation, the secondary sustained pressor response characteristic of SHR, but not of WKY, persisted in captopril-treated SHR at a smaller magnitude and a shorter duration. These results indicate that the normalization of arterial blood pressure in SHR upon chronic oral treatment with angiotensin-converting enzyme inhibitor is associated with changes in properties of RVL cardiovascular neurons towards those of WKY. This suggests that brain angiotensin and RVL cardiovascular neurons play interactive roles in the development of hypertension in SHR.