DOPAMINERGIC RECEPTOR-MEDIATED EFFECTS IN THE MESENTERIC VASCULATURE AND RENAL VASCULATURE OF THE CHRONICALLY INSTRUMENTED NEWBORN PIGLET

Objective: To determine the effects of stimulation of vascular dopamin ergic receptor subtype 1 (dopamine-1) receptors in the renal and mesen teric vascular beds of a neonatal model. Design: Prospective, unblinde d, dose response evaluation in an awake animal. Setting: University re search laboratory. Subjects: Thirty newborn piglets, obtained and inst rumented at 1 to 3 days of age and studied 48 hrs later. Interventions : Animals were chronically instrumented with transit time ultrasound f low probes around the left renal and superior mesenteric arteries. The y were then intravenously infused with either dopamine (2 to 32 mu g/k g/min) or fenoldopam (1 to 100 mu g/kg/min), which is a selective agon ist of the dopamine-1 receptor. Measurements and Main Results: Blood p ressure was only significantly increased by the highest infusion rate of dopamine (32 mu g/kg/min), from a mean of 78 mm Hg at baseline to 8 7 mm Hg. Mesenteric and renal vascular resistances were unchanged by d opamine at any dose. Dopamine at 32 mu g/kg/min decreased renal blood flow by 16.6 +/- 19.6 (SD) % and increased renal vascular resistance b y 39.6 +/- 41.1% (p < .05). Mesenteric blood flow in creased by 15% at 32 mu g/kg/min (p < .05) but mesenteric vascular resistance was not a ffected by dopamine. Fenoldopam reduced blood pressure at infusion rat es of 5, 10, and 100 mu g/kg/min. Fenoldopam had no effect on renal va scular resistance at any dose. Fenoldopam reduced mesenteric vascular resistance at 5 mu g/kg/min and at all higher doses. Conclusions: Thes e data demonstrate the absence of dopaminergic receptor-mediated vasod ilation in the porcine neonatal renal vascular bed. In the mesenteric artery, dopamine-1 receptor-mediated vasodilation may be obtained. Dop amine itself, probably because of stimulation of other receptors, caus es renal artery vasoconstriction and does not increase superior mesent eric artery blood flow.