Effects of Captopril on Vascular Noradrenergic Transmission in SHR

The effects of captopril, 3 and 10 mg/kg, on vascular noradrenergic transmission were examined in vivo in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). These experiments were performed on mesenteric vascular beds perfused in situ. In WKY, 3 mg/kg captopril failed to significantly lower mean arterial blood pressure (MAP) and also failed to have a significant effect on the frequency-response curve to sympathetic nerve stimulation or doseresponse curve to norepinephrine (NE) in the mesentery of WKY. In SHR mesentery, 3 mg/kg captopril failed to alter the frequency-response curve or NE dose-response curve, while it significantly lowered MAP. The higher dose of captopril, 10 mg/kg, also failed to lower MAP in WKY mesentery, although it caused some reduction in pressor responses to sympathetic nerve stimulation and NE. In SHR mesentery, 10 mg/kg captopril significantly lowered MAP and reduced pressor responses to both nerve stimulation and NE. It should be noted, however, that captopril lowered responses to nerve stimulation and NE to a similar degree in both SHR and WKY, and there was no indication of a prejunctional action on vascular noradrenergic transmission. In conclusion, although captopril was more effective in lowering MAP in SHR than in WKY, no evidence was found for significantly greater facilitation of vascular sympathetic neurotransmission by endogenous angiotensin II in SHR than in WKY, and most of the actions of captopril on vascular neurotransmission appeared to be postjunctional in nature and unrelated to either the renin-angiotensin system or the kallikrein-kinin system.