Ontogeny of renal beta adrenoceptors in the sheep

The renal vasodilatory response to beta-2 adrenoceptor stimulation is greater in fetal than adult sheep. Since this phenomenon could not be explained by differences in cAMP-mediated events, we examined the ontogeny of renal beta adrenoceptor subtypes by radioligand binding using the beta adrenergic antagonist 125I-pindolol. The specific binding of 125I-pindolol was saturable, reversible, and stereoselective. Competition studies using the selective beta-1 and beta-2 adrenergic antagonists (ICI 89406 and ICI 118551, respectively) revealed two beta adrenoceptor subtypes in adult kidneys but only the beta-2 subtype in fetal kidneys. Preincubation of renal cortical membranes with either the beta-1 or the beta-2 adrenergic antagonist prior to competition studies in adult kidneys decreased specific binding and resulted in the detection of only one beta adrenoceptor subtype. Preincubation of fetal kidneys with the beta-1 adrenergic antagonist did not affect binding characteristics; preincubation of fetal kidneys with the beta-2 adrenergic antagonist markedly decreased specific binding from 64 +/- 2% (n = 4) to 29 +/- 2% (n = 3) (P less than 0.05). Analysis of Rosenthal plots revealed similar beta adrenoceptor densities and affinities between fetal and adult kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)