Solute and Water Transport along an Inner-medullary Collecting Duct Undergoing Peristaltic Contractions.

In this study, we investigate the mechanism by which about half of the bolus volume is reabsorbed into the collecting duct cells despite the short contact time. To accomplish that, we develop a dynamic mathematical model of solute and water transport along a collecting duct of a rat papilla undergoing peristaltic contractions. The model predicts that, given pre-existing axial concentration gradients along the loops of Henle, approximately 40% of the bolus volume is reabsorbed as the bolus flows down the inner-medullary collecting duct. Additionally, simulation results suggest that while the contraction-induced luminal hydrostatic pressure facilitates water extraction from the bolus, that pressure is not necessary to concentrate the bolus. Also, neither the negative interstitial pressure generated during the relaxation phase nor the concentrating effect of the hyaluronic acid has a significant effect on bolus concentration. Taken together, these findings indicate the high collecting duct apical water permeability allows a substantial amount of water to be extracted from the bolus, despite its short transit time. However, the potential role of the peristaltic waves in the urine concentrating mechanism remains to be revealed. PMID: 31313955 [PubMed - as supplied by publisher]
Source: American Journal of Physiology. Renal Physiology - Category: Physiology Authors: Tags: Am J Physiol Renal Physiol Source Type: research