New morphological evidence for a mechanism of lymph formation in skeletal muscle.

A new mechanism of lymph formation associated with pulsation and vasomotion of arterioles is proposed in skeletal muscle. To provide evidence for this proposal, an investigation of the lymphatic vessels in the spinotrapezius muscle of the rat was undertaken. The lymphatics were visualized by microinjection of a contrast medium (Evans blue albumin), and histological sections of the muscle were prepared and examined with the light and the electron microscope. The studies indicated that lymphatics ranging in size from 20 to 200 micron in this skeletal muscle have no smooth muscle but only a thin lining of endothelium. All lymphatics lie in immediate proximity to the arcading and transverse arterioles and occasional muscular venules, and appeared to be wrapped around them. It was further observed that when the arterioles were dilated, the contiguous lymphatics were partially or completely collapsed, whereas lymphatics around contracted arterioles were wide open. No significant deformation of the adjacent skeletal muscle cells was observed. These results suggest that the contraction of vascular smooth muscle, as well as pulsatile elastic distension of arterioles, may cause periodic changes in lymphatic volume and thereby serve as peristaltic mechanisms for lymph transport. Vascular smooth muscle may thus influence not only blood flow in the microcirculation, but also water transport in the interstitium and into the lymphatics.