Prenatal glucocorticoids stimulate neonatal juxtamedullary proximal convoluted tubule acidification

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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 μg/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 < 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 < 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 < 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)-carboxyflourescein 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 < 0.001). Basolateral Na(HCO3)3 symporter proton flux was 106.1 ± 10.0 pmol·mm-1·min-1 in control animals and 202.6 ± 17.8 pmol·mm-1·min-1 in the dexamethasone group (P < 0.001). Thus prenatal dexamethasone stimulates juxtamedullary PCT HCO3 absorption in part by increasing apical Na+-H+ antiporter and basolateral Na(HCO3)3 symporter activity. These data are consistent with a role for glucocorticoids in proximal tubular maturation.

Original languageEnglish (US)
Pages (from-to)F746-F752
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume261
Issue number5 30-5
DOIs
StatePublished - Jan 1 1991

Keywords

  • Bicarbonate absorption
  • In vitro microperfusion
  • Renal development
  • Volume absorption

ASJC Scopus subject areas

  • Physiology

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