Water transport in the immature rabbit collecting duct

Abstract

 Immature animals have limited ability to concentrate the urine. This is in part the result of end-organ resistance to arginine vasopressin (AVP). To characterize this response, we measured water absorption in microperfused cortical collecting ducts (iCCD) and outer medullary CD (iOMCD) derived from 2- to 12-day-old rabbits. The roles of adenosine 3′,5′-cyclic monophosphate (cAMP) and prostaglandins were investigated. Baseline osmotic water permeability (L_p, 10⁻⁷ cm/atm per s) in the iCCD (20.3±2.4) and iOMCD (19.7±5.6) was not different from mature CCD (mCCD) (14.6±3.1). After AVP, L_p in the iCCD (46.7±10.0) was significantly lower than in the mCCD (114.3±21.8). Neither stimulation with cAMP (85.6±51.3) nor inhibition of endogenous prostaglandin production with indomethacin (57.6±29.8) abolished the blunted response to AVP in the iCCD. We conclude that AVP-stimulated water transport in the iCCD is impaired. The disruption in AVP response is, at least in part, localized distal to cAMP, and is not mediated by prostaglandins.