Regulation of thick ascending limb transport by vasopressin

Body fluid tonicity is controlled largely through the regulation of renal w ater excretion mediated by the peptide hormone vasopressin (1). Renal water conservation occurs as a result of the combined functions of the loop of H enle and the collecting duct, both of which are regulated by vasopressin. T he loop of Henle is responsible for countercurrent multiplication, a proces s that concentrates the interstitial fluid of the renal medulla relative to the systemic plasma. The collecting duct is the site at which water permea bility is regulated by vasopressin to result in variable osmotic equilibrat ion with the hypertonic medullary interstitium. In this brief review, we su mmarize current knowledge regarding the role of the thick ascending limb in the regulation of renal water excretion by vasopressin.