PRESYNAPTIC α_2-ADRENOCEPTOR MEDIATED REGULATION OF NOREPINEPHRINE RELEASE IN PERFUSED MESENTERIC VASCULATURES IN YOUNG AND ADULT SPONTANEOUSLY HYPERTENSIVE RATS

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The present study was designed to evaluate the role of the presynaptic α_2-adrenoceptor in the pathogenesis of hypertension. Norepinephrine overflow during sympathetic nerve stimulation and its changes by presynaptic α_2-adrenoceptor inhibition were examined in the perfused mesenteric vasculatures of young and adult spontaneously hypertensive rats (SHR) compared with age-matched Wistar Kyoto rats (WKY). Electrical sympathetic nerve stimulation caused significantly greater overflow of endogenous norepinephrine from the adrenergic nerve terminals in young SHR than in age- matched WKY. Yohimbine, an α_2-adrenoceptor blocking agent, facilitated norepinephrine overflow from the adrenergic nerve terminals. The effects of yohimbine on norepinephrine overflow and pressor responses to electrical nerve stimulation were less in young SHR than in age-matched WKY. Norepinephrine overflow in adult SHR was similar to that in adult WKY, and differences in the effect of yohimbine on norepinephrine overflow between SHR and WKY were not marked at this chronic stage. These results suggest that enhanced norepinephrine overflow in the mesenteric vasculatures can be observed only in young SHR; this may be due in part to an impaired negative feed-back mechanism on the nerve terminals by presynaptic _2-adrenoceptors.
社団法人日本循環器学会の論文
1987-01-20