Effects of epinephrine on the renal vascular bed of fetal, newborn, and adult sheep.

The renal hemodynamic response to renal artery infusions of epinephrine were compared in conscious and chronically instrumented fetal (125-139 days gestation; term 145 days), newborn (5-13 days postnatal), and nonpregnant adult sheep. Epinephrine produced similar dose related decreases in renal blood flow velocity in all three groups. The mean estimated concentration of epinephrine in renal blood producing a 50% decrease in renal blood flow velocity, ED50, was 0.008 microgram/ml. Epinephrine infusions during renal alpha-adrenoceptor blockade with phentolamine produced increases in renal blood flow velocity that were of greater magnitude in fetal compared to newborn and adult sheep. The maximal increase in renal blood flow velocity observed were 57 +/- 11%, 22 +/- 3%, and 18 +/- 3% in fetal, newborn, and adult sheep, respectively (p less than 0.001). This vasodilation produced by epinephrine during alpha-adrenoceptor blockade was completely inhibited by ICI 118,551, a beta 2-adrenoceptor antagonist. Inhibition of renal vascular beta-adrenoceptors with propranolol in fetal sheep did not enhance alpha-adrenoceptor-mediated renal vasoconstriction with epinephrine infusions. Results of the present study demonstrate similar renal vasoconstrictor responses to renal artery infusion of epinephrine in fetal, newborn, and adult sheep. In contrast, the renal vasodilator responses observed with epinephrine infusions during renal alpha-adrenoceptor blockade were greater in fetal compared to newborn and adult sheep. However, epinephrine-mediated renal vasoconstriction was not enhanced by blockade of beta-adrenoceptors in fetal sheep.