Interaction between endothelin and angiotensin II in the up-regulation of vasopressin messenger RNA in the inner medullary collecting duct of the rat

Recent studies in our laboratory have demonstrated that angiotensin (ANG) II and endothelin (ET) 1 up-regulate the expression of arginine vasopressin V2 receptor in the inner medullary collecting duct (IMCD) of the rat. The present studies were performed to explore the interaction between ANG II and ET-1 in up-regulating the expression of arginine vasopressin V2 receptor in the IMCD of the rat. Two sets of studies were done. In the first set of studies, rat IMCD tissue was isolated and incubated with ANG II in combination with ETA or ETB antagonist. In the second set of experiments, rat IMCD tissue was incubated with ET-1 with ANG receptor antagonist saralasin. Tissue samples were then analyzed by means of quantitative reverse transcriptase polymerase chain reaction and Western blotting. The ANG II treatment resulted in increased V2 messenger RNA (mRNA) from control level of 138 ± 12 amol/μg of total RNA to 385 ± 63 amol/μg of total RNA (P < .01). The ANG II/ETA treatment resulted in no significant decrease in V2 mRNA expression (319 ± 59 amol/μg of total RNA), whereas ET-1/ETB antagonist and ET-1/ETA/ETB antagonist treatments resulted in reducing V2 mRNA to control levels of 214 ± 25 and 176 ± 22 amol/μg of total RNA, respectively. The ET-1 treatment increased V2 mRNA expression from control level of 221 ± 25 amol/μg of total RNA to 383 ± 43 amol/μg of total RNA (P < .02). The ET-1-induced increase in V2 mRNA expression was significantly reduced to control level (210 ± 36 amol/μg of total RNA) after saralasin treatment. Western blotting revealed that changes in protein expression in the different treatment conditions were comparable with changes in V2 mRNA expression. These data suggested that the up-regulation of V2 receptor induced by ANG II and ET-1 is mediated by both vasoconstricting hormones. These 2 systems interact in up-regulating the expression of V2 receptors in the kidney.