Ontogeny of alpha-adrenoceptor responses in renal vascular bed of sheep.
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.
Matherne
G P
GP
Department of Pediatrics, University of Iowa College of Medicine, Iowa City 52242.
Nakamura
K T
KT
Robillard
J E
JE
D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure / Q000187:drug effects; D005333:Fetus / Q000502:physiology; D006143:Guanabenz / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics; D007668:Kidney / Q000098:blood supply* / Q000196:embryology / Q000254:growth & development; D010656:Phenylephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012016:Reference Values; D012039:Regional Blood Flow / Q000187:drug effects; D012756:Sheep; D014661:Vasoconstriction / Q000187:drug effects
D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D006143:Guanabenz