Permeability of pancreatic capillaries to small molecules

The permeability of capillaries in the isolated, blood-perfused canine pancreas was studied with the double-indicator dilution technique. The permeability-surface area products (PS) for inulin and beta-lactoglobulin A were determined at different plasma flows (attained by pump perfusion). The PS for inulin increased with increasing plasma flow, while the PS for beta-lactoglobulin A was relatively independent of plasma flow. At the highest plasma flow acquired, PS for inulin and beta-lactoglobulin A were approximately 23 and 3.5 ml X min-1 X 100 g-1, respectively. The ratio of the PS values for these two solutes was greater than the ratio of their free diffusion coefficients, indicating restricted diffusion of beta-lactoglobulin A relative to inulin. The degree of restriction was consistent with a maximum equivalent pore radius of 67 A for pancreatic capillaries. An ultrastructural analysis revealed that ductal as well as acinar and islet capillaries were fenestrated. The permeability characteristics of fenestrated pancreatic capillaries are similar to those previously reported for the small intestine.