AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 2 277-R283, Copyright © 1988 by American Physiological Society
Ontogeny of alpha-adrenoceptor responses in renal vascular bed of sheep
G. P. Matherne, K. T. Nakamura and J. E. Robillard
Department of Pediatrics, University of Iowa College of Medicine, Iowa City 52242.
The renal hemodynamic response to renal arterial infusions of guanabenz
(alpha 2-adrenoceptor agonist) and phenylephrine (alpha 1-adrenoceptor
agonist) were compared in conscious and chronically instrumented fetal
(132-140 days gestation; term 145 days), newborn (6-15 days postnatal), and
nonpregnant adult sheep. Phenylephrine produced similar dose-related
decreases in renal blood flow velocity in all three groups at low
concentrations (less than 1.8 X 10(-7) M) of drug in renal blood, whereas
at the highest concentration adults demonstrated the most vasoconstriction
and newborns the least (P less than 0.05 ANOVA). Responses to phenylephrine
infusion during renal alpha 1-adrenoceptor blockade with prazosin were
completely inhibited. Guanabenz produced greater renal vasoconstriction in
adult sheep (P less than 0.05 ANOVA) at all concentrations (0.6 X 10(-6) to
8 X 10(-6) M) when compared with fetal and newborn sheep.
Guanabenz-mediated vasoconstriction was not affected by alpha
1-adrenoceptor blockade with prazosin but was completely inhibited by the
addition of an alpha 2-adrenoceptor antagonist idazoxan. Results of the
present study demonstrate that renal vasoconstriction is mediated by both
alpha 1- and alpha 2-adrenoceptors in fetal, newborn, and adult sheep.
Moreover, these results suggest that renal alpha 1- and alpha
2-adrenoceptor-mediated vasoconstrictor responses mature at different
rates.
