THE MICROVASCULAR STRUCTURE OF THE NORMAL COLON IN RATS AND HUMANS

The colonic microcirculation may be expected to have a central role in the absorptive, secretory, and protective functions of the colon, To characterize the microvascular structure of the colon in rats and huma ns, microvascular casts were prepared and examined by scanning electro n microscopy. Quantitative measures of the microvasculature were obtai ned from histological sections, The overall organization of microvesse ls was found to be similar in the rat and human colon, Capillaries in the colonic mucosa formed a honeycomb-like network around each of the mucosal glands. This capillary plexus was supplied by arterioles which divide into their capillary branches at the level of the submucosa, M ucosal capillaries drain into venules at the luminal surface of the mu cosa. Venules then pass to submucosal veins without receiving further capillary branches. Examination of vascular casts also showed that in both the rat and the human colon, there was an increased density of su bluminal capillaries in the cecum and proximal colon compared to that of the rest of the colon, This was supported by quantitative measures which indicated a significantly greater microvascular surface area in the rat cecum (24.1 mm(2)/mm(3)) compared to that of the midcolon (19. 8 mm(2)/mm(3)) (P = 0.04) and the distal colon (19.1 mm(2)/mm(3)) (P = 0.03), Similarly in the human colon there was a significantly greater total microvascular volume in the proximal colon (13.4%) compared to that of the distal colon (7.7%) (P < 0.0005) and there was a significa ntly greater total microvascular surface area in the proximal colon (2 2.4 mm(2)/mm(3)) compared to that of the distal colon (17.5 mm(2)/mm(3 )) (P = 0.032), This study details quantitative vascular data for the colon in rats and humans which has not previously been documented, des pite its important role in the absorptive function of the colon and in many disease processes affecting the colon, These data provide the no rmal values with which pathological conditions of the colon which affe ct the vasculature can be compared. (C) 1996 Academic Press, Inc.