Effects of alpha- and beta-adrenoceptor blockade on the neurally evoked overflow of endogenous noradrenaline from the rat isolated heart.
beta-Adrenoceptor blockade by propranolol (4 X 10(-6)M) was without effect on the overflow of endogenous noradrenaline from the isolated heart of the rat induced by stimulation of sympathetic nerves for 1 min at 1 and at 4 Hz. The increase in heart rate in response to such stimulation was abolished by propranolol treatment. alpha 2-Adrenoceptor blockade by yohimbine (10(-6)M) induced approximately a two fold increase in the overflow of endogenous noradrenaline induced by stimulation of sympathetic nerves for 1 min at 1 and at 4 Hz. A combination of yohimbine (10(-6)M) and desipramine (10(-7)M) induced a more than 3 fold increase in the overflow of endogenous noradrenaline produced by sympathetic nerve stimulation at 1 and at 4 Hz. Heart rate increases produced by such stimulation were intensified. These results provide no evidence for the feedback stimulation of presynaptic beta-adrenoceptors in this preparation. The action of alpha-2-blockade was equipotent at stimulation frequencies of 1 and 4 Hz.
D000818:Animals; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000378:metabolism*; D011433:Propranolol / Q000494:pharmacology*; D051381:Rats; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism*; D015016:Yohimbine / Q000494:pharmacology*
D015016:Yohimbine; D011433:Propranolol; D009638:Norepinephrine