Regional Differences in Rates of Insorption of Sodium and Water from the Human Large Intestine

Abstract

Regional differences in sodium and water fluxes across the mucosa of the human colon were sought by comparing the arterial appearances of isotopes of sodium and water after instillation of test solutions containing them into four parts of the large intestine. Deuterium oxide and 24Na, in isotonic sodium chloride (154 mM), were placed in the cecum, transverse colon, descending colon, or rectum. The times of appearance and concentration of isotopes in serial samples of arterial blood were integrated with known plasma–disappearance curves to obtain rates of unidirectional flux from colonic lumen to blood (insorption). A gradient of insorption was found. Insorption was most rapid in the cecum and decreased progressively in the transverse colon, descending colon, and rectum. During steady-state perfusion of the entire large intestine the insorption rates of sodium and water, calculated by disappearance of isotopes from the lumen, were intermediate between those observed in the cecum and transverse colon during regional studies. Perfusion studies also revealed a close correlation between insorption and net absorption of sodium and water, implying that a regional gradient of net absorption may exist in the large intestine, analogous to the observed insorption gradient.