Interference by inhibitors of the renin-angiotensin system with neurogenic vasoconstriction

In the pithed rat preparation captopril, enalapril, teprotide and saralasin given intravenously attenuated pressor responses to both spinal sympathetic nerve stimulation and exogenous noradrenaline, indicating that angiotensin has a potent adrenergic facilitating action. Bi-lateral nephrectomy abolished the effects of captopril on nerve stimulation but responses to noradrenaline were still inhibited following nephrectomy, indicating that part of the post-junctional actions of captopril might not be angiotensin dependent. Both phenylephrine and clonidine are also inhibited by captopril in the pithed rat. It is thus not clear whether captopril is interacting with post-junctional alpha 1- or alpha 2-adrenoceptors. Vasoconstrictor responses to nerve stimulation are greater in SHR than WKY and captopril is more effective at inhibiting responses in the SHR than it is in WKY. These interactions between captopril and the sympathetic nervous system could explain the effectiveness of ACE inhibitors as antihypertensive agents.