COMPARATIVE-ANALYSIS OF INSULO-ACINAR PORTAL SYSTEM IN RATS, GUINEA-PIGS, AND DOGS

The insulo-acinar portal system in the rat, guinea pig, and dog was co mparatively analyzed using corrosion casting method in scanning electr on microscopy and confocal laser scanning microscopy. In all animals e xamined, there were three types of arterioles according to their desti nation: 1) the arteriole which supplied the capillary glomerulus of th e islet, 2) the arterioles which directly branched out into capillarie s around the acini, and 3) the arterioles which supplied the duct syst em. In the rat, the afferent vessel usually ended in the cortical laye r of the islet and its main branches ran along this layer before givin g secondary capillary branches into the deeper regions, while in the d og and guinea pig, the region where the afferent arterioles branched o ut into secondary capillary branches varied among individual islets. T here were three types of efferent vessels of the islet: 1) the insulo- acinar portal vessels that radiated from the islet to join the capilla ry network in the exocrine pancreas, 2) the emissary venules of the is let, leading directly into the systemic circulation, and 3) the insulo -ductal portal vessels which drained into the peri-ductal capillary ne twork. In the rat and guinea pig, the intralobular islets possessed bo th the insulo-acinar portal vessels and the emissary venules, while th e interlobular islets possessed emissary venules with occasionally occ urring insulo-acinar portal vessels. In the dog, most of the islets we re located within the lobule and possessed preferentially the insulo-a cinar portal vessels. In this animal, the lobule was supplied by sever al microvascular units, in the center of which was located the capilla ry glomerulus of the islet. The peri-insular zone of the unit was main ly supplied by the insulo-acinar portal vessels, while the periphery, the tele-insular zone, was directly supplied by arterioles as well. Th e venules originated at the periphery of the unit. The islet in the do g had virtually no emissary venules. Confocal laser scanning microscop y of the rat islets showed that B cells occupied the core of all islet s. The microvascular architecture within the rat islet appeared to be organized as to drain blood from the A and D cell area to the B cell a rea of the islet. (C) 1997 Wiley-Liss, Inc.