Intestinal capillary filtration in experimental diabetes mellitus.

There is indirect evidence that indicates that intestinal transcapillary fluid and solute exchange is significantly altered in diabetes mellitus. To directly assess the dynamics of microvascular fluid and solute exchange in the small intestine (jejunum-ileum), we measured lymph flow, capillary pressure, capillary filtration coefficient, plasma and lymph oncotic pressures, and the osmotic reflection coefficient in anesthetized, fasted control rats and in rats in which diabetes was induced by a single injection of streptozotocin (65 mg/kg ip) 4 wk before the experiments. Diabetes was associated with an increase in lymph flow (by 120%), capillary pressure (by 34%), and capillary filtration coefficient (by 75%) when compared with values from control rats. The transcapillary oncotic pressure gradient was not altered by diabetes. Interstitial fluid pressure, calculated from the measured parameters in the Starling equation, was increased from -1.6 mmHg in control rats to +2.5 mmHg in diabetic animals. Analysis of lymph-to-plasma protein concentration ratios at various lymph flows suggests that the osmotic reflection coefficient in the diabetic intestine is comparable to that obtained in control animals. The results of this study indicate that experimental diabetes mellitus is associated with increases in intestinal capillary pressure and capillary filtration rate but that intestinal capillary permeability is not altered in this disorder.