Selective Venoconstriction by Dopamine in Comparison with Isoproterenol and Phenylephrine

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Abstract
Patients [73] who underwent aortocoronary saphenous-vein bypass graft of 1 to 3 vessels were selected for study. Ten patients given no drug served as controls. Small and insignificant changes in perfusion pressure and blood level in the oxygenator were recorded between 15 and 30 min of perfusion. Phenylephrine (0.3 mg) significantly increased perfusion pressure and the volume of blood in the oxygenator, whereas 0.08 mg isoproterenol decreased perfusion pressure without altering reservoir volume significantly. Dopamine was initially administered to 4 patients by i.v. infusion at 0.01 mg/kg per min. A marked increase in reservoir volume (mean 875 ml) occurred, without change in perfusion pressure. Since dose was less precisely controlled by this method, single intra-arterial injections of 0.2 mg dopamine increased reservoir volume in the oxygenator without change in perfusion pressure. In subsequent patients doses of dopamine were increased in incremental fashion to identify a dose that would also increase perfusion pressure. Single doses of 0.4, 0.8, 1.0, 1.2, 2.4 and 4.0 mg diluted to 20 ml were each given to 2 or 3 patients. No consistent increase in perfusion pressure was observed until the 4.0-mg dose was administered. After all doses of dopamine, blood reservoir volume increased. To determine whether the venoconstriction of dopamine was mediated by stimulation of .alpha.-adrenergic or dopaminergic receptors, an additional 5 patients were given 10 mg phentolamine before dopamine and phenylephrine. Phentolamine tended to reduce perfusion pressure and reservoir volume, but these changes were small. Dopamine (0.2 mg) was administered 2 min after phentolamine. The characteristic rise in reservoir volume was not observed. Phenylephrine (0.3 mg) was then administered within 5 min after phentolamine, and also had no significant effect on perfusion pressure or reservoir volume. When drugs were administered intra-arterially, peak effect was observed within 30 s and duration was short. The effects of phenylephrine lasted 15-20 min, dopamine, 12-15 min and isoproterenol, 8-10 min.
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