Hypotensive Action of Captopril in Spontaneously Hypertensive and Normotensive Rats

SUMMARY The effects of captopril and angiotensin II on adrenergic neurotransmission have been studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). In a pithed rat preparation, vasoconstrictor responses evoked by spinal stimulation were greater in SHR than WKY (p < 0.01). Captopril reduced responses to electrical stimulation and this reduction was greater in the SHR (p < 0.001). Bilateral nephrectomy reduced the vasoconstrictor responses to nerve stimulation in both strains of rat and abolished the effects of captopril. In an isolated perfused mesenteric artery preparation, responses to nerve stimulation in the absence of angiotensin II were greater in SHR than WKY (p < 0.05). Angiotensin II potentiated responses from both strains of rat, however the ampli-tude of the potentiation was greater in preparations from the SHR than those from WKY (p < 0.002). Captopril (30 mg/kg by mouth) reduced blood pressure in conscious SHR over a 5-day dosing period. In WKY rats, no hypotensive action of captopril was observed. However, in another normotensive strain, the Alderley Park Wistar rat (APW), captopril lowered blood pressure. Plasma renin activity was not significantly different among these three strains of rat. The APW have previously been shown to be very sensitive to the adrenergic potentiating actions of angiotensin II. Captopril thus lowers blood pressure in SHR and APW, and both these strains are sensitive to the adrenergic potentiatin