Metabolism of vasopressin.

The clearance of vasopressin (VP) by the kidneys and splanchnic viscera was studied in the anesthetized dog. VP is bound to plasma protein, 10% at basal plasma VP levels and 40% at plasma VP concentrations greater than 20 microU/ml. The urinary clearance of VP is 70-100% of the glomerular filtration rate; the renal organ clearance of the hormone is 20-30% greater than its urinary clearance. There is evidence that the renal organ clearance of VP is affected by changes in both glomerular filtration rate and renal blood flow. The renal clearance of VP is a result of glomerular filtration, degradation, or reabsorption in the proximal nephron, and secretion into the distal nephron. In the short term, the renal clearance of VP is unaffected either by changes in the plasma VP concentration over a broad range or by moderate hemorrhage. The splanchnic clearance of VP is accomplished almost equally by the intestine and the liver. Because the sum of the splanchnic and renal clearances of VP is less than estimates of its metabolic clearance rate, there may be a physiologically significant clearance of VP by organs in addition to the kidneys and splanchnic viscera.