Evidence for a countercurrent exchanger in the intestinal villi of suckling swine

Abstract

The possible existence of a countercurrent exchanger (multiplier) in the intestinal villi of suckling swine was investigated with three different methods: (1) Comparing venous appearance of oxygen and red cells in the mesenteric vein after close i.a. injection of a blood sample equilibrated with pure oxygen and containing methaemoglobinaemic red cells. (2) Determining sodium (micrograms) over protein (mg) ratios along villi. (3) Estimating tissue osmolality in the villus tissue from measurements of freezing-point depression. It was observed that oxygen appeared earlier than red cells in the mesenteric vein after i.a. injection. Furthermore, both the chemical measurements of sodium/protein ratios in the villi and the estimations of tissue osmolality indicate that there exists a gradient of osmolalities along the villus length, the villus tip being hyperosmolar as compared to the villus base. We conclude that a countercurrent exchanger (multiplier) exists in the villi of suckling swine. Its possible pathophysiological significance is discussed.