Long-term regulation of inner medullary collecting duct urea transport in rat

Facilitated urea transport is regulated acutely by arginine vasopressin (AVP) and hyperosmolality in rat terminal inner medullary collecting duct (IMCD). This study tested whether chronic diuresis or antidiuresis regulates facilitated urea transport. Basal and AVP-stimulated urea permeabilities (P-urea) were measured in perfused IMCD subsegments, Rats were made: (1) diuretic by giving them sugar water (with or without food) or furosemide; or (2) antidiuretic by water deprivation. They were then compared with untreated rats given food and water ad libitum. Terminal TMCD from untreated rats had a high basal P-urea that was significantly increased by AVP. Diuresis significantly increased basal P-urea in terminal IMCD in all five diuresis protocols. Water deprivation for 1 or 3 d bad no effect on basal or AVP-stimulated P-urea in the IMCD2 subsegment of the terminal IMCD, In contrast, 3 d of water deprivation significantly increased both basal and AVP-stimulated P-urea in the IMCD, subsegment; 1 d of water deprivation had no effect on basal or AVP-stimulated P-urea. Next, initial IMCD (IMCD1) were studied. Initial IMCD from untreated rats had a low basal P-urea that was not increased by AVP (10 nM). Water diuresis (with or without food) for 3 to 5 d had no effect on basal P-urea but significantly increased AVP-stimulated P-urea. Furosemide diuresis and water diuresis for 1 or 7 d had no effect on either basal or AVP-stimulated P-urea in initial IMCD. Water deprivation for 2 to 3 d, but not for 1 d, significantly increased basal P-urea in initial IMCD, whereas water deprivation for 1 d increased AVP-stimulated P-urea. It is concluded that chronic changes in hydration cause heterogeneous changes in facilitated urea transport in rat IMCD subsegments.