Inhibition of norepinephrine release by presynaptic alpha 2-adrenoceptors in mesenteric vasculature preparations from chronic DOCA-salt hypertensive rats.

This study investigated norepinephrine release during electrical nerve stimulation and inhibitory characteristics of presynaptic alpha 2-adrenoceptors in perfused mesenteric vasculature from deoxycorticosterone acetate (DOCA)-salt hypertensive rats (7-8 weeks after surgery). Electrical stimulation of sympathetic innervation caused a significantly greater release of endogenous norepinephrine into the mesenteric vasculature of DOCA-salt hypertensive rats than in age-matched normotensive controls. Pressor responses to electrical nerve stimulation were also enhanced in DOCA-salt hypertension. Yohimbine, a potent alpha 2-adrenoceptor blocking agent, potentiated the stimulation-evoked release of norepinephrine into the vasculature in normotensive rats. This effect was blunted in DOCA-salt hypertension. These results suggest that increased norepinephrine release from the sympathetic nerve endings in DOCA-salt hypertension might partly reflect an impaired presynaptic alpha 2-adrenoceptor-mediated inhibition, which could enhance vascular sympathetic tone in this model of hypertension.