Structural organization of the initial lymphatics in the monkey mesentery and intestinal wall as revealed by an enzyme-histochemical method.

The structure and distribution of the initial lymphatics in whole mount preparations of the mesentery and intestinal walls of the Japanese monkey (Macaca fuscata) were studied using an enzyme-histochemical method (Kato et al., 1991, 1993). The lymphatic walls, colored dark brown by their positive 5'-nucleotidase (5'-Nase) activity, were clearly distinguished from the blood vessels (especially capillaries and arterioles) which were colored blue due to their positive alkaline phosphatase activity. The specificity and localization of both enzyme reactions were confirmed by comparative histochemical studies of the same specimen under a light microscope and scanning or transmission electron microscopes. Application of this staining method takes advantages of the overview preparation of flat membranous organs. The mesenterial area was generally lobulated in distribution with collecting lymphatics and blood vessels. At about the center of each lobule enclosed by the vessels, 5'-Nase-positive initial lymphatics assumed tubulo-saccular shapes, branching antler-like figure to form dense networks in the main lymph vascular pathway. Their apical parts revealed marked knob-like blind endings demarcated by a thin endothelial wall. No direct interconnection was recognizable between the lymphatic space and the tissue interstitium as a prelymphatic fluid pathway. In such preparations, 5'-Nase-positive lymphatic islands could be found isolated from the lymphatic network.