The role of coronary alpha 1-adrenoceptors of the dog heart in dopamine-induced cardiostimulation evidenced by treatment with prazosin.
To assess the participation of postjunctional coronary alpha 1-adrenoceptors in the dopamine-induced general circulatory stimulation, pentobarbital-anesthetized open chest dogs were infused with the agent (1-16 micrograms.kg-1.min-1 i.v.) before and after the administration of the alpha 1-selective adrenergic antagonist prazosin (0.15 mg.kg-1). Coronary responses were characterized by the changes of blood flow (electromagnetic flowmeter) and those of calculated vascular conductance. Left ventricular contractile force was measured with a strain gauge arch. In the control state, whereas coronary blood flow increased simultaneously with the dose-dependent hypertensive effect of dopamine, the calculated augmentation of coronary vascular conductance was relatively slight (maximum: greater than or equal to 50%) compared to the very great increase of cardiac inotropism (up to greater than or equal to 250%) and myocardial O2 consumption (up to greater than or equal to 250%). After blocking the alpha 1-adrenoceptors, in spite of the elimination of the hypertensive effect, the inotropic and blood flow actions of dopamine remained unaltered and the calculated value of vascular conductance indicated an enhanced vasodilation (up to 200%). The alpha 2-blocker yohimbine (0.5 mg.kg-1) failed to elicit actions of similar magnitude. It was concluded that postjunctional alpha-adrenoceptor-dependent coronary vasoconstrictor influences compete with metabolically coupled vasodilation during the cardiostimulatory action of dopamine.
Kékesi
V
V
Clinic of Cardiovascular Surgery, Semmelweis University Medical School, Budapest, Hungary.
Rabloczky
G
G
Mader
M R
MR
Juhász-Nagy
A
A
D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects*; D004285:Dogs; D004298:Dopamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006321:Heart / Q000187:drug effects*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D011224:Prazosin / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology*
D011942:Receptors, Adrenergic, alpha; D014662:Vasoconstrictor Agents; D015016:Yohimbine; D004298:Dopamine; D011224:Prazosin