title: An analysis of some factors influencing alpha-adrenoceptor feed-back at the sympathetic junction in the rat heart.
abstract: 1 The effects of the selective prejunctional alpha-adrenoceptor antagonist, yohimbine, on the cardioacceleration responses to sympathetic stimulation were examined in the pithed rat. 2 Yohimbine reversed the inhibitory effects of the alpha-adrenoceptor agonist, clonidine, on the stimulation-induced tachycardia. 3 Yohimbine failed to potentiate significantly responses to stimulation in the absence of clonidine when stimulation was applied at the optimal level for cardiac responses (C6-T1). 4 When the pithing rod electrode was moved to T2-T6, cardioaccelerator responses were smaller and yohimbine produced potentiation at frequencies of greater than or equal to 1 Hz. This potentiation was prejunctional since responses to exogenous noradrenaline (NA) were not increased by yohimbine. 5 In the presence of cocaine, potentiation by yohimbine could be shown at the lower frequency of 0.1 Hz. 6 The possible physiological significance of a negative feed-back effect of noradrenaline on cardiac sympathetic nerves is discussed.
mesh_terms: D000315:Adrenalectomy; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D004558:Electric Stimulation; D005246:Feedback; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009469:Neuromuscular Junction / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D003042:Cocaine; D003000:Clonidine; D009638:Norepinephrine