1623 RENAL ALPHA (α) AND BETA (β) ADRENERGIC RESPONSE IN FETAL AND ADULT SHEEP: DEMONSTRATION OF BETA-2 (β₂) VASODILATION IN FETUSES

Abstract

Effects of intrarenal boluses of epinephrine (E) (0.00625 to 0.2 ug/kg of B.W.) on renal blood flow (RBF) were studied in chronically catheterized fetal (F) lambs (125-137 days; term 145 days) and adult (A) sheep using a doppler flowmeter. Effects of E alone and during α, α1, and β2 adrenergic blockade were studied. Blood pressure was unchanged during E infusion. The E dose that reduced RBF (%ΔRBF) by 50% (ED₅₀) was 0.0014 ug/kg/ml RBF in F and 0.0001 ug/kg/ml RBF in A; this response was blocked by the α₁ antagonist prazosin. Following α blockade with phentolamine, E produced vasodilation (%Δ RBF-α) in F and A which was blocked by the β₂ antagonist butoxamine. When E was given during α blockade at a dose equal to ED₅₀ for vasoconstriction, E produced a 33% rise in RBF in F and 10% in A (p<0.05).

Present results demonstrate that: 1) the E dose required for vasoconstriction, which is α1 mediated, is 10 times greater in F than A, 2) the lower α receptor response in F may be secondary to the greater β₂ receptor activity than in A.

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