In vivo observation of the lymphatic system in the rat stomach.

The anatomy of the lymphatic system in the rat stomach was studied by means of fluorescent in vivo microscopy. A fluorescein-albumin conjugate was injected via a micropipette into the mucosa, submucosa, or muscularis externa. The movement of the conjugate was visualized using a closed-circuit television system. When injected into the base of the mucosa, the conjugate was seen to flow from the deposited pool. These fluorescent streams, 21-53 micron in diameter, formed a network in the base of the mucosa and superficial submucosa. They were in close approximation to, but separate from, the arterioles and venules. These fluorescent channels are probably lymphatic microvessels, as they were connected to larger lymphatic vessels running parallel to the large arterioles and venules in the deep submucosa. These larger lymphatic vessels passed through the muscularis externa and drained into extragastric lymphatic vessels on the lesser or greater curvature. There was no network of lymphatic microvessels in the deep submucosa or muscularis externa. The extragastric lymphatic vessels, 50-340 micron in diameter, had valves and displayed spontaneous contractions, moving the conjugate toward the lymph nodes.