This experiment was performed to determine the causes Of circulatory activities during muscular work, to evaluate the effect of various kinds of painful stimuli to the knee joint on the Cardiovascular system, and to compare the effect ofjoint pain on the cardiovascular system with that of skeletal muscle pain on the cardiovascular system.

In this experiment, blood pressure, heart rate and the impulse discharges of cardiac sympathetic efferents were recorded to evaluate the changes of circulatory activities in the baroreceptor of denervated cats anesthetized with α-chloralose.

The results are summarized as follows;

1. Rhythmic flexions and extensions of a knee joint in its physiological working range have an influence on circulatory activities in 11 out of 14 units. This effect disappeared after the cutting of the posterior and medial articular nerve.

2. Inward and outward rotations were extended into the noxious range, significant increase in the circulatory activities were elicited. The increases in circulatory activities induced by noxious outward rotation exceeded those elicited by noxious inward rotation.

3. Injection of KCI into the knee joint triggered circulatory reflexed that may indicate a nociceptive response in 17 out of 22 units. An injection of bradykinin into the knee joint elevated the circulatory activities in 11 out of 23 units, it produced biphasic responses or a fall in blood pressure, and on the other hand, it increased heart rate and impulse discharges of cardiac sympathetic efferents.

4. The increases in circulatory activities induced by the injection of KCI and bradykinin into the gastrocnemius muscle exceeded those induced by the injection of KCI and bradykinin into the knee joint.

5. A IV stimulus to the medial articular nerve. which could not excite the Group IV units, induced increases in circulatory activities at a 20V stimulus. which Could excite all medial articular nerve afferents.

It can be coiiclued thatpassive movements of the knee joint activate a sympathetic otittlo%k to the cardiovascular system as various kinds of painful stimuli (mechanical, chemical. electrical) in baroreceptor denervated cats anesthetized with α-chloralose.