LONG-TERM ELECTRICAL-STIMULATION OF RABBIT SKELETAL-MUSCLE INCREASES GROWTH OF PAIRED ARTERIES AND VEINS

We tested whether chronic stimulation of skeletal muscle can increase the growth of paired arteries and veins in rabbit extensor digitorum longus muscle (EDL). The right EDL of female New Zealand White rabbits was stimulated via the common peroneal nerve at 10 Hz using 300 mu s square waves at 3-4 V. Two-hour periods of stimulation were alternated with 4-h periods of rest, 7 days/wk for similar to 60 days. The left EDL served as control. The hindlimb vascular system was maximally dilated and perfuse-fixed with 3% glutaraldehyde and 2% paraformaldehyde at arterial and venous pressures of 80-100 and 15-20 mmHg, respectively. Muscles were postfixed in OsO4 and embedded in EPOX 812 resin. One millimeter-thick transverse sections were cut at uniform locations through the entire breadth of the muscle and analyzed using videomicroscopy along with computerized morphometric and stereological techniques. All paired arteries and veins on each full muscle section were analyzed. Chronic muscle stimulation caused the wall volume of paired arteries and veins to increase by an average of approximately twofold and the lumen volume to increase by an average of approximately threefold compared with the contralateral control muscles. The wall-to-lumen area ratio of the arteries and veins was not affected. Muscle stimulation also caused the numerical density of arteries having a diameter > 100 mu m to increase by approximately fourfold and the density of veins having a perimeter >500 mu m to increase by similar to 10-fold. The length of paired arteries and veins increased by an average of approximately twofold during the similar to 60 days of stimulation, but the tortuosity of the arteries did not increase. Increased length in the absence of increased tortuosity indicates that new artery-vein pairs were formed. The results therefore support the hypothesis that long-term stimulation of skeletal muscle causes a structurally based increase in diameter along with proportionate growth of the media and the formation of entirely new artery-vein pairs.