title: Prenatal programming of rat proximal tubule Na+/H+ exchanger by dexamethasone.
abstract: Prenatal administration of dexamethasone causes hypertension in rats when they are studied as adults. Although an increase in tubular sodium reabsorption has been postulated to be a factor programming hypertension, this has never been directly demonstrated. The purpose of this study was to examine whether prenatal programming by dexamethasone affected postnatal proximal tubular transport. Pregnant Sprague-Dawley rats were injected with intraperitoneal dexamethasone (0.2 mg/kg) daily for 4 days between the 15th and 18th days of gestation. Prenatal dexamethasone resulted in an elevation in systolic blood pressure when the rats were studied at 7-8 wk of age compared with vehicle-treated controls: 131 +/- 3 vs. 115 +/- 3 mmHg (P < 0.001). The rate of proximal convoluted tubule volume absorption, measured using in vitro microperfusion, was 0.61 + 0.07 nl.mm(-1).min(-1) in control rats and 0.93+ 0.07 nl.mm(-1).min(-1) in rats that received prenatal dexamethasone (P < 0.05). Na(+)/H(+) exchanger activity measured in perfused tubules in vitro using the pH-sensitive dye BCECF showed a similar 50% increase in activity in proximal convoluted tubules from rats treated with prenatal dexamethasone. Although there was no change in abundance of NHE3 mRNA, the predominant luminal proximal tubule Na(+)/H(+) exchanger, there was an increase in NHE3 protein abundance on brush-border membrane vesicles in 7- to 8-wk-old rats receiving prenatal dexamethasone. In conclusion, prenatal administration of dexamethasone in rats increases proximal tubule transport when rats are studied at 7-8 wk old, in part by stimulating Na(+)/H(+) exchanger activity. The increase in proximal tubule transport may be a factor mediating the hypertension by prenatal programming with dexamethasone.
authors.affiliation: Department of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9063, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Dagan
authors.forename: Jyothsna
authors.initials: J
authors.lastname: Gattineni
authors.forename: Vodi
authors.initials: V
authors.lastname: Cook
authors.forename: Michel
authors.initials: M
authors.lastname: Baum
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology*; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D010477:Perfusion; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D005938:Glucocorticoids; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers; D003907:Dexamethasone