Effects of endothelin on neuroeffector junction in mesenteric arteries of hypertensive rats.

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Abstract
The effect of endothelin, a novel vasoconstrictor peptide, on the adrenergic neuroeffector junction was investigated in isolated perfused mesenteric arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The vasoconstrictor responses to periarterial sympathetic nerve stimulation and exogenous norepinephrine were determined. Infusion of endothelin-1 increased the baseline perfusion pressure dose dependently to similar extents in the two strains. A subpressor dose of endothelin-1 (10(-10) M) enhanced the pressor response to norepinephrine; its effect was greater in WKY rats than in SHR. Endothelin-1 (10(-12) to 10(-10) M) attenuated the pressor response to sympathetic nerve stimulation, and the degree of inhibition tended to be less in SHR than in WKY rats. Higher doses (3 x 10(-10) and 10(-9) M) of endothelin-1 enhanced the pressor response to nerve stimulation in both WKY rats and SHR. Endothelin-1 inhibited norepinephrine release from rat mesenteric arteries; the inhibition was significantly less in SHR than in WKY rats. These results suggest that endothelin enhances the responsiveness of alpha-adrenergic receptors to catecholamines, whereas it inhibits presynaptic adrenergic neurotransmission. Thus, endothelin can interact with the neuroeffector junction in addition to having a vasoconstricting effect in peripheral vessels. The difference in the mode of modulation by endothelin at the vascular neuroeffector junction in SHR from that in WKY rats might explain the maintenance of hypertension.