AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 4 990-R998, Copyright © 1994 by American Physiological Society
Ontogenic changes in renal response to alpha 1-adrenoceptor stimulation in sheep
E. N. Guillery, J. L. Segar, D. C. Merrill, K. T. Nakamura, P. A. Jose and J. E. Robillard
Department of Pediatrics and Cardiovascular Center, University of Iowa College of Medicine, Iowa City 52242.
The present study was designed to examine the effect of direct intrarenal
infusion of the alpha 1-adrenoceptor agonist, phenylephrine, on urinary
flow rate (UFR) and on renal Na and Cl excretion in conscious and
chronically instrumented fetal (128-133 days gestation, term 145 days),
newborn (6-12 days), and adult sheep. Five different renal concentrations
of phenylephrine, varying from 5 +/- 1 to 72 +/- 2 ng/ml, were studied. Low
renal phenylephrine concentration (< or = 12 +/- 1 ng/ml) induced a
significant renal vasoconstrictor response in fetuses but not in newborn
and adult sheep. The effects of intrarenal phenylephrine infusion on UFR
and fractional excretion of Na (FENa) was greater (P < 0.05) in newborn
lambs than in fetal and adult sheep. At a renal concentration of
phenylephrine between 9 +/- 1 and 12 +/- 1 ng/ml, the percent decrease in
UFR was greater (P < 0.05) in newborn lambs (-19.1 +/- 4.7%) than in
fetal (9.8 +/- 8.9%) and adult sheep (-3.3 +/- 3.9). The percent decrease
in FENa at renal concentration of phenylephrine between 18 +/- 1 and 24 +/-
1 ng/ml was also significantly (P < 0.05) larger in newborn lambs (-20.2
+/- 2.8%) than in fetal (-8.0 +/- 3.1%) and adult sheep (-11.2 +/- 2.6%).
In summary, the present results indicate that the fetal kidney has a
limited ability to increase sodium reabsorption in response to stimulation
of alpha-adrenoceptors and that the effect of renal alpha-adrenoceptor
stimulation on urinary volume and urinary sodium excretion increases during
the newborn period.
