title: Prenatal glucocorticoids stimulate neonatal juxtamedullary proximal convoluted tubule acidification.
abstract: The rate of neonatal proximal convoluted tubule (PCT) HCO3 absorption is lower than that of adult animals. The present in vitro microperfusion study examined whether prenatal dexamethasone (60 micrograms/kg daily to the doe for 3 days before delivery) would accelerate the maturation of neonatal juxtamedullary PCT acidification. Control neonates studied within 48 h of birth had a urine pH of 7.06 +/- 0.15 and a urine HCO3 concentration of 34.3 +/- 7.0 meq/l. Animals receiving dexamethasone had a urine pH of 6.47 +/- 0.11 and a urine HCO3 concentration of 10.1 +/- 4.0 meq/l, both of which were significantly lower than control (P less than 0.01). In juxtamedullary PCTs perfused in vitro, volume absorption was 0.27 +/- 0.03 nl.mm-1.min-1 in controls and 0.39 +/- 0.02 nl.mm-1.min-1 in dexamethasone-treated animals (P less than 0.05). HCO3 absorption was stimulated in the dexamethasone group (52.6 +/- 4.6 vs. 34.1 +/- 6.3 pmol.mm-1.min-1, P less than 0.05); however, glucose transport was not significantly affected (24.8 +/- 1.3 in dexamethasone vs. 21.5 +/- 3.5 pmol.mm-1.min-1 in controls). Intracellular pH was measured using 2',7'-bis(carboxyethyl)-5(6)-carboxyflourescin to examine whether prenatal dexamethasone stimulated the apical Na(+)-H+ antiporter and the basolateral Na(HCO3)3 symporter. Apical Na(+)-H+ antiporter proton flux was 108.5 +/- 14.2 pmol.mm-1.min-1 in the control group and 250.7 +/- 31.3 pmol.mm-1.min-1 in the dexamethasone group (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235-9063.
authors.forename: M
authors.initials: M
authors.lastname: Baum
authors.forename: R
authors.initials: R
authors.lastname: Quigley
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001639:Bicarbonates / Q000097:blood / Q000652:urine; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007606:Juxtaglomerular Apparatus / Q000187:drug effects / Q000502:physiology*; D007684:Kidney Tubules / Q000187:drug effects / Q000502:physiology*; D008431:Maternal-Fetal Exchange; D011247:Pregnancy; D011817:Rabbits; D012016:Reference Values
chemical_list: D001639:Bicarbonates; D003907:Dexamethasone