Impaired intestinal absorption of vitamin D3 in azotemic rats.

Changes in vitamin D metabolism and their effect on calcium and bone metabolism in uremia have been extensively studied. However, the possible effect of uremia on intestinal absorption of vitamin D has not been investigated. We determined the rate of intestinal absorption of vitamin D3 in uremic and normal rats using a well-defined in vivo perfusion technique under identical experimental conditions. The rate of jejunal absorption of vitamin D3 in uremic animals (5.09 +/- 1.87 pmol/100 cm/h) was significantly less (p less than 0.001) than that found in the control animals (11.5 +/- 1.6 pmol/100 cm/h). While the underlying mechanism(s) of the observed reduction in vitamin D absorption in uremia is not known, its recognition adds another dimension to the previously recognized abnormalities of vitamin D metabolism in uremia.

Selective impairment of nutrient absorption from intestines with chronic venous hypertension.

Malnutrition is frequently associated with advanced cirrhosis. To investigate the role of portal hypertension in nutritional impairment, we developed an animal model to isolate and characterize the effects of chronic intestinal venous hypertension on intestinal nutrient absorption. We performed mesenteric arteriovenous anastomosis combined with portal vein banding in rats. Hepatic architecture and excretory function (bile flow and bile salt output) were unaltered, while severe and persistent intestinal venous hypertension was produced. We then measured in vivo absorption rates of three test nutrients (vitamin D3, valine, and tryptophan) and water. Vitamin D3 absorption was significantly impaired by intestinal congestion, while amino acid absorption was unaffected. Splanchnic hypertensive rats absorbed less water than controls. We conclude that chronic intestinal venous hypertension alone selectively impairs nutrient absorption.