Water transport in the immature rabbit collecting duct

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.