Inhibitory action on alpha-human atrial natriuretic polypeptide on vascular adrenergic neurotransmission is attenuated in spontaneously hypertensive rats.

The purpose of the present study is twofold, firstly to investigate the effects of alpha-human atrial natriuretic polypeptide (alpha-hANP) on norepinephrine overflow from sympathetic nerve endings, and secondly to compare vascular responsiveness in perfused mesenteric preparations in spontaneously hypertensive rats (SHR, Okamoto and Aoki, 7-9 weeks old) and a cohort of Wistar Kyoto rats (WKY). In preliminary studies using normotensive Wistar rats, the pressor responses to electrical nerve stimulation or exogenous norepinephrine application were inhibited by alpha-hANP. Norepinephrine overflow was also suppressed by alpha-hANP, during nerve stimulation. The pressor responses and norepinephrine overflow during nerve stimulation were significantly greater in SHR than in WKY rats. The inhibitory effect of alpha-hANP on these responses was reduced in SHR. These results indicate that alpha-hANP could affect both pre- and post-synaptic sites of the resistance vessels. Further, the reduced inhibition of pressor responses and norepinephrine overflow by alpha-hANP in SHR suggests an insufficient regulation of adrenergic transmission by alpha-hANP in hypertension.