Structural relationship between microlymphatic and microvascullar blood vessels in the rabbit ventricular myocardium

We investigated the distribution and relationship between draining lymphatic vessels, lymphatic capillaries, and microvascular blood vessels in rabbit ventricular tissue. The left and right ventricular tissue from 15 healthy adult rabbits was obtained, processed, and sectioned for analysis. 5'-nucleotidase-alkaline phosphatase (5'-Nase-Alpase) double staining was first used to identify lymphatic and blood vessels. Dual fluorescent immunohistochemical technique was then utilized with lymphatic endothelial cell marker podoplanin and blood vascular marker PAL-E. In addition, five ventricular samples were examined for ultrastructure using transmission electron microscopy (TEM). Draining lymphatic vessels and both lymphatic and blood capillaries were observed in the ventricular tissue. The lumens of draining lymphatic vessels were larger and irregular while the lymphatic capillaries were small in diameter and abundant. All lymphatic vessels were located among blood capillaries in the myocardium and aligned with the longitudinal axis of myocardial cells. The immunofluorescence double staining demonstrated that draining lymphatic vessels, lymphatic capillaries, and microvascular blood vessels were adjacent to each other and the cardiac myocyte with a ratio of lymphatic to microvascular blood vessels of approximately 1:1. This study suggests that lymphatic and blood capillaries exist in abundance and in nearly identical numbers in the ventricular myocardium and that they interweave with each other to comprise a complicated vessel network.