Maturation of HCO3- transport in rabbit collecting duct.
Newborn rabbits maintain a state of hypochloremic metabolic alkalosis with plasma HCO3- concentrations generally exceeding 27 mM. The large amounts of potential net base in mother's milk probably contribute to the generation of this alkalosis. We surmised that immature handling of H+ or HCO3- by the neonatal collecting duct helps maintain this alkalosis. Net HCO3- transport was measured in perfused collecting ducts taken from maturing rabbits, in solutions simulating adult rabbit plasma ultrafiltrate and then in presence of Cl(-)-free bathing solution. Cortical collecting ducts (CCD) from newborn and 4-wk-old rabbits failed to secrete HCO3- under baseline conditions and could not be stimulated to secrete HCO3- in Cl(-)-free bath. Neonatal segments perfused at very slow flow rates showed significant HCO3- absorption; inhibition of HCO3- secretion by removal of luminal Cl- revealed a substantial HCO3- absorptive flux. Segments from 6-wk-old and mature animals secreted net HCO3- and generally showed more than a fivefold increase in HCO3- secretion after Cl- removal from the bath. Outer medullary collecting ducts (OMCD) from newborn rabbits absorbed HCO3- at rates approaching that of mature segments. We conclude that relatively high rates of HCO3- absorption in OMCD and lack of HCO3- secretion in CCD may contribute to the metabolic alkalosis of the neonatal rabbit.
Mehrgut
F M
FM
Department of Pediatrics, Albert Einstein College of Medicine, Bronx, New York 10461.
Satlin
L M
LM
Schwartz
G J
GJ
D000042:Absorption; D000375:Aging / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001639:Bicarbonates / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000494:pharmacology; D066298:In Vitro Techniques; D007672:Kidney Cortex; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D010477:Perfusion; D011817:Rabbits
D001639:Bicarbonates; D002712:Chlorides