Morphological and physiological characteristics of pancreas-specific venular permeability induced by Monastral blue B

Leaky blood vessels in the microcirculation can be detected in vivo by injecting an animal with colloidal pigments such as Monastral blue B (MbB) or carbon black. We have previously used the MbB labeling method in the spontaneously diabetic BB/W or rat and detected increased vascular permeability restricted to the venules of the pancreas. We now report the morphological and physiological characteristics of this phenomenon in additional rat strains. Susceptibility to pancreatic labeling with MbB among strains was found to be a highly variable, heritable characteristic, but in no strain did vessels label in any organ other than the pancreas. Pancreatic labeling by MbB was dose dependent, was observed in both inbred and outbred rats, and was not related to major histocompatibility complex haplotype. Enhanced permeability was induced by MbB within minutes of its administration as a result of the formation of gaps between endothelial cells; these gaps then closed within 15 min. Pretreatment with silica or carrageenan, agents known to affect macrophage function, completely blocked pancreatic MbB venular labeling, but the effect was reversible over a period of several days. We hypothesize that presence of MbB in the pancreatic circulation induces organ-specific venular leakage either by a direct effect on pancreatic endothelial cells or via the local release of a mediator.