Epinephrine Facilitates Neurogenic Responses in Isolated Segments of Dog Mesenteric Arteries

Summary: Epinephrine (EPI) bitartrate (10-9-10-8 M) significantly enhanced tension development in response to electrical field stimulation in isolated segments of dog mesenteric arteries. Responses to exogenous norepinephrine (NE) were generally unaffected, indicating that the EPI-induced increases in response to field stimulation are not explicable in terms of changes in postjunctional sensitivity. The facilitatory effects of EPI (5 × 10-9 M) were unaffected by atenolol (10-6 M) but were completely abolished by timolol (2 × 10-7 M), suggesting an involvement of β2-adrenoreceptors in mediating the EPI-induced facilitation of neurogenic responses. Responses to exogenous NE were usually unaffected by either β-adrenoreceptor antagonist. The results suggest that release of endogenous sympatheitc neurotransmitter, measured in terms of postjunctional effects on vascular smooth muscle tone, appears to be modulated by prejunctional facilitatory β2-adrenoreceptors and that these receptors may be a physiologic site of action of EPI.