Effects of alpha-human atrial natriuretic peptides on neurosecretion and vascular responsiveness in spontaneously hypertensive rats

Effects of alpha-human atrial natriuretic peptides (alpha-hANP) on the norepinephrine overflow from the sympathetic nerve endings and vascular responsiveness were investigated in the perfused mesenteric intestinal loop preparations from 7- to 9-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY). Pressor responses to electrical nerve stimulation or exogenous norepinephrine were inhibited by alpha-hANP (3.4 X 10(-7) to 1.0 X 10(-6) mol/l), and norepinephrine overflow during the nerve stimulation was concomitantly suppressed by alpha-hANP. The pressor responses and norepinephrine overflow by nerve stimulation were greater in SHR than the age-matched WKY, while the inhibition of these responses by alpha-hANP was significantly less in SHR than in WKY. These results demonstrate that alpha-hANP could affect both pre- and post-synaptic sites of the resistance vessels, and less reduction in the pressor responses and norepinephrine overflow by alpha-hANP in SHR suggests insufficient regulation of adrenergic neurotransmission by cardiac peptide in hypertension.