title: Presynaptic modulation of heart rate responses to cardiac nerve stimulation in pithed rats.
abstract: The effects of presynaptic alpha-adrenoceptor blockade with phentolamine, before and after inhibition of uptake-1 with cocaine, on the positive chronotropic response to cardiac sympathetic nerve stimulation in pithed rats was investigated. Phentolamine or cocaine each enhanced the cardiac responses to stimulation at 1 Hz for 15 sec by 10-25%; the combination of the drugs caused no greater enhancement than did either drug alone. Cocaine considerably potentiated the tachycardia produced during prolonged stimulation at 0.1 but not at 0.2-1 Hz. Phentolamine potentiated the responses to stimulation at 0.2 and 0.5 Hz by 21 and 12%, respectively, but not those at 0.1 or 1 Hz. After cocaine, phentolamine caused a further small increase in the response at 0.1 Hz but not other frequency. It is concluded that presynaptic alpha-adrenoceptors exert only modest control over the responses of the rat heart to cardiac nerve stimulation and that this modulation is little influenced by uptake-1.
mesh_terms: D000818:Animals; D003042:Cocaine / Q000494:pharmacology; D003891:Desipramine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006321:Heart / Q000294:innervation*; D006339:Heart Rate; D008297:Male; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D003042:Cocaine; D003891:Desipramine; D009638:Norepinephrine; D010646:Phentolamine