Ontogeny of renal beta-adrenoceptor-mediated vasodilation in sheep: comparison between endogenous catecholamines

The renal hemodynamic response to renal arterial infusions of norepinephrine was compared to epinephrine infusions during renal alpha-adrenoceptor blockade in chronically instrumented and unanesthetized fetal (127-141 days gestation; term 145 days), newborn (6-10 days old), and nonpregnant adult sheep. Infusions of either catecholamines produced renal vasodilation which was of greater magnitude in fetal compared to newborn and adult sheep. Maximal increases in renal blood flow velocity during norepinephrine infusion were 64 +/- 5% in fetal, 23 +/- 4% in newborn, and 24 +/- 7% in adult sheep (p less than 0.001). Similar age-dependent increases in renal blood flow velocity were observed during epinephrine infusion, with maximal changes being 74 +/- 10% in fetal, 23 +/- 4% in newborn, and 19 +/- 4% in adult sheep (p less than 0.001). Increases in renal blood flow velocity produced by both norepinephrine and epinephrine infusions were completely inhibited by intrarenal infusion of ICI 118,551, a beta 2-adrenoceptor antagonist. Taken together, these results suggest that the renal vascular beta 2-adrenergic receptor that mediates vasodilation may be stimulated by both norepinephrine and epinephrine with equal potency. In addition, results of this study demonstrate that enhanced beta 2-adrenoceptor mediated renal vasodilatory capacity is observed during fetal life.