The effect of alpha-adrenergic blockade on the pulmonary vascular response to dopamine in neonatal lambs.
The effect of alpha-adrenergic blockade by phentolamine on the pulmonary vascular response to dopamine was studied in chronically prepared newborn lambs. Dopamine was administered at doses of 2.7 micrograms . kg-1 . min-1, 27 micrograms . kg-1 . min-1 and 270 micrograms . kg-1 . min-1 with and without alpha-adrenergic blockade. Dopamine infusion at 270 micrograms . kg-1 . min-1 caused a rise in the mean pulmonary artery pressure from 22 +/- 3.2 mmHg (mean +/- S.E.) at baseline to 36 +/- 4.1 mmHg (P less than 0.001). This rise was unaffected by alpha-adrenergic blockade. Dopamine infusion alone did not change pulmonary blood flow, but, in the presence of alpha-adrenergic blockade, pulmonary blood flow rose from 190 +/- 12 ml . min-1 . kg-1 at baseline to 280 +/- 13 ml . min-1 . kg-1 at the maximum dopamine infusion rate (P less than 0.001). Pulmonary vascular resistance was the same before and after alpha-adrenergic blockade and did not change from the baseline value during dopamine infusion.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D004298:Dopamine / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology*; D011651:Pulmonary Artery / Q000187:drug effects*; D014655:Vascular Resistance / Q000187:drug effects*
D000317:Adrenergic alpha-Antagonists; D004298:Dopamine; D010646:Phentolamine