EFFECTS OF INTRARENAL ADMINISTRATION OF DOPAMINE (DA) ON RENAL BLOOD FLOW (RBF) IN CONSCIOUS FETAL AND ADULT SHEEP IN VITRO DA RECEPTOR FINDINGS

Abstract

Effects of intrarenal boluses of OA (0.125 to 16 ug/kg of body wt.) on RBF were studied in chronically catheterized fetal (F) lambs (129-137 days; term 145 days) and adult (A) sheep. Changes in RBF were continuously monitored by doppler flowmeter. Effects of DA alone and during α and β adrenergic blockade were studied. Blood pressure was unchanged during DA infusion. DA alone in F produced no change in RBF (%ΔRBF) at doses 2 ug/kg decreased RBF in a dose response relation (r=0.84). Decreased RBF in A was seen only at >8 ug/kg. F were less sensitive to DA than A when DA was corrected for RBF (ug/kg/ml RBF). Following adrenergic blockade (%ΔRBF-B), DA produced vasodilation in F and A; the DA dose required for vasodilation was 10 times greater in F than A. In vitro DA-receptor characterization was done using the opposite kidney removed at surgery. Similar DA receptor affinity between F (Kd 66.3±10.4 nM) and A (Kd 70.5±6.4 nM) as well as DA receptor density (1.08±0.13 and 0.90±0.22 pM/mg protein respectively) were found. Present results demonstrate that DA has less vasodilatory effect in F than A during adrenergic blockade but this effect is not secondary to a difference in receptor affinity or density, suggesting a post-receptor phenomenon.