ARGININE VASOPRESSIN AND ATRIAL-NATRIURETIC-PEPTIDE DO NOT ALTER ION-TRANSPORT BY CULTURED FETAL DISTAL LUNG EPITHELIUM

Previous studies have shown that i.v. arginine vasopressin (AVP) decreases but does not stop lung fluid secretion in term fetuses not in labor. Although it has been presumed that the response to AVP results from augmented sodium transport, there is controversy whether AVP actually does affect sodium transport in mammalian lung epithelium. To determine if AVP or aldosterone could alone or together augment sodium transport in the perinatal lung, we studied primary cultures of fetal rat distal lung epithelium in Ussing chambers. The short circuit current of these sodium-transporting cells was not affected by the application of either 30 or 300 mU/mL AVP whether or not they were previously exposed to aldosterone (10(-6) M). Aldosterone also did not affect the baseline bioelectric properties. Short circuit current increased in response to 8-bromo cAMP (10(-4) M) and +/- 3-isobutyl-1-methylxanthine (10(-3) M) to levels 169 +/- 16 (SEM) and 172 +/- 7% of respective baseline values. AVP had no effect in cells pretreated with 3-isobutyl-1-methylxanthine. Monolayers also did not respond to atrial natriuretic peptide (10(-11) to 10(-8) M). Monolayers of Na-absorbing A6 renal epithelium did increase short circuit current with either aldosterone or AVP. AVP increased endogenous cAMP levels in A6 but not fetal rat distal lung epithelium cells, suggesting that fetal rat distal lung epithelium lacks V2 receptors. These studies demonstrate that AVP does not increase ion transport in cultured fetal distal lung epithelium although these cells possess the necessary second messenger system.