The functional characteristics of tendon blood circulation in the rabbit hindlimbs.

Neurohormonal, mechanical, and muscle exercise effects on tendon blood flow were studied in thirty-five rabbits. After anesthesia by urethane, experiments were performed on in situ preparation of the hindlimb under stable state in systemic blood pressure. Tendon and muscle blood flow were measured simultaneously by the hydrogen gas clearance method, and their temperature and PO2 were continuously observed by thermocouple and oxygen sensor, respectively. The resting blood flow in the denervated tendon tibialis anterior, gastrocnemius, and soleus (ml/(100 g.min] was 39.0 +/- 4.0, 34.5 +/- 8.2, and 30.2 +/- 4.3, respectively, whereas in their muscles it was 17.8 +/- 1.5, 17.1 +/- 2.1, and 12.6 +/- 1.1, respectively. The tendon tissue temperature and PO2 increased gradually until 15-20 min after cutting the sciatic nerve, and the increasing rate depended upon the initial control level before denervation. Intravenous injection of noradrenaline in the dose of 1-9.9 micrograms/kg produced a marked decrease in the tendon tissue temperature of the tibialis anterior, but a mild one in the muscle. The longitudinal tension force produced a decrease in the tendon tissue temperature of the tibialis anterior, but no change in the muscle. During muscle exercise, tendon blood flow and temperature tended to decrease, whereas the muscle blood flow and temperature increased markedly from the beginning of muscle exercise. There was no evidence to demonstrate the existence of exercise hyperemia in the tendon tissue. These data suggest that tendon blood circulation can be modified by many factors, and that mechanical and exercise effects may play a role in regulation of tendon blood flow channels and fluid transfer for the lubrication of tendon fiber movements.