Effect of prazosin on the cardiopulmonary response to dopamine in awake lambs: comparison with phentolamine and tolazoline.
Combination vasodilator and cardiotonic therapy may help infants with pulmonary vasospasm and low cardiac output. We previously have shown that the alpha 1- and alpha 2- blocking agents tolazoline and phentolamine, plus dopamine, improved cardiac output relative to dopamine alone, without changing pulmonary vascular resistance. To similarly test an agent with selective alpha 1-receptor blocking action, prazosin, we instrumented 6 newborn lambs to measure the pressure in the pulmonary artery, aorta and left atrium and cardiac output. After recovery, the lambs were studied while awake and breathing room air. The response to dopamine, at doses of 2.7, 27 and 270 micrograms/kg/min, was measured alone, and again on a different day after prazosin (1 mg/kg). Dopamine alone raised systemic, pulmonary and left atrial pressure, and systemic vascular resistance at high doses. Pulmonary vascular resistance did not change. Prazosin prevented the dopamine-induced systemic resistance increase and permitted cardiac output to rise relative to dopamine alone (p less than 0.0125), but barely blunted the dopamine-induced pulmonary pressure increase (p less than 0.005 vs. base in both groups). These results are similar to those previously found with tolazoline and phentolamine. Thus, all the tested alpha-blockers facilitate the cardiotonic effect of dopamine, but none ablates its pulmonary pressure effect.
Drummond
W H
WH
Department of Pediatrics, University of Florida, Gainesville.
Williams
B J
BJ
Dailey
W A
WA
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001784:Blood Gas Analysis; D004298:Dopamine / Q000494:pharmacology*; D006321:Heart / Q000187:drug effects*; D008168:Lung / Q000187:drug effects*; D010646:Phentolamine / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology*; D011652:Pulmonary Circulation / Q000187:drug effects; D012756:Sheep; D014043:Tolazoline / Q000494:pharmacology*
D014043:Tolazoline; D004298:Dopamine; D011224:Prazosin; D010646:Phentolamine