Ontogenic changes in renal response to alpha 1-adrenoceptor stimulation in sheep.
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.
Guillery
E N
EN
Department of Pediatrics and Cardiovascular Center, University of Iowa College of Medicine, Iowa City 52242.
Segar
J L
JL
Merrill
D C
DC
Nakamura
K T
KT
Jose
P A
PA
Robillard
J E
JE
D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure / Q000187:drug effects; D002712:Chlorides / Q000652:urine; D004305:Dose-Response Relationship, Drug; D005314:Embryonic and Fetal Development; D005260:Female; D005865:Gestational Age; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006340:Heart Rate, Fetal / Q000187:drug effects; D007262:Infusions, Intravenous; D007668:Kidney / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009638:Norepinephrine / Q000378:metabolism; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology*; D011247:Pregnancy; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D012016:Reference Values; D012079:Renal Circulation / Q000187:drug effects* / Q000502:physiology; D012756:Sheep; D012964:Sodium / Q000652:urine; D014556:Urine / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects
D002712:Chlorides; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; D012964:Sodium; D009638:Norepinephrine