Electrical pulses appear in the inferior vena cava and abdominal aorta at contraction of leg muscles.

A vascular-interstitial neuromuscular closed circuit is described anatomically and electrically. The neuromuscular unit has a high resistance due to its axons. The "outer" vascular-interstitial branch has a low resistance due to a large cross section area. When a rat spontaneously contracts leg muscles after pinching a toe, electric potential pulses appear inside the inferior vena cava, between vena cava and peritoneum, between aorta and peritoneum, between vena cava and peritoneum and between aorta and subcutis. Minor pulses between electrodes in the peritoneal fluid are interpreted as induced by the intravascular potential pulses. The use of Ag-AgCl electrodes or platinum electrodes does not appreciably change the results.