In Vivo Documentation of an Arteriovenous Shunt in Rat Pancreatic Acinar Tissue

With the use of epiilumination fluorescence microscopy, we demonstrate for the first time in vivo the existence and function of direct arteriovenous communication (arteriovenous shunt) in rat pancreatic acinar tissue. In eight Sprague-Dawley rats the corpus and tail of the pancreatic gland were reviewed for arteriovenous anastomoses. In seven animals the technique did not allow us to visualize completely the arteriolar and venular vascular system due to overlying pancreatic tissue. In one animal, however, the vascular trees could be identified in their continuity over a length of several millimeters, including an arteriovenous shunt with a diameter of 12.0 microns. Analysis of volumetric blood flow revealed that 86.2% (15.61 nl/min) of the arteriolar blood volume was shunted into the venule, while only 13.8% (2.50 nl/min) of the blood volume was carried by the arteriole distal to the arteriovenous shunt to the nutritive capillary bed. There were no changes in diameter, i.e., vasoconstriction, vasodilation, or vasomotion, over an observation period of 30 min, indicating that, at least under physiological conditions, this arteriovenous communication functioned as a real "fare-through" channel.