Nifedipine prevents sympathetic vasoconstriction distal to severe coronary stenoses.
Cardiac sympathetic nerve stimulation ( CSNS ) can induce vasoconstriction distal to severe coronary stenoses by activation of vascular alpha 2-adrenoceptors. Whether nifedipine can antagonize this CSNS -induced vasoconstriction was tested in 11 anesthetized, vagotomized dogs. CSNS decreased the end-diastolic resistance of intact coronary arteries from 0.76 +/- 0.07 to 0.56 +/- 0.05 mm Hg x min x 100 g/ml (p less than 0.05). In contrast, the resistance distal to severe stenoses, which were defined by a reduction of the postocclusive reactive hyperemia to almost zero, was increased during CSNS from 0.52 +/- 0.06 to 0.87 +/- 0.14 mm Hg x min x 100 g/ml (p less than 0.05). This increase in resistance was associated with severe ischemia, as indicated by a net lactate production of the circumflex-perfused myocardium and a decrease in systolic segment shortening from 8.4 +/- 0.7 to 7.0 +/- 0.7% (p less than 0.05). Both intracoronary (10 micrograms) and intravenous (10 micrograms/kg) administration of nifedipine did not change the poststenotic resistance at rest, but did prevent the CSNS -induced increase in resistance, the decrease in regional contraction, and the net lactate production. We conclude that nifedipine can prevent the deleterious role of alpha-adrenoceptor-mediated vasoconstriction in the genesis of myocardial ischemia.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001157:Arterial Occlusive Diseases / Q000503:physiopathology*; D003327:Coronary Disease / Q000503:physiopathology*; D003331:Coronary Vessels / Q000502:physiology; D004285:Dogs; D004558:Electric Stimulation; D006321:Heart / Q000294:innervation* / Q000502:physiology; D009543:Nifedipine / Q000008:administration & dosage / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects*; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009543:Nifedipine