STIMULATION OF GROUP-III AND GROUP-IV AFFERENT NERVES FROM THE HINDLIMB BY THROMBOXANE-A(2)

These experiments were designed to test the hypothesis that the TxA(2) mimetic, U46,619, would stimulate group III and IV afferent nerve end ings from the hindlimb of the anesthetized cat. Nerve impulses were re corded from the dorsal rootlets of the L7-S1 segments of the spinal co rd, and afferent units identified by measurement of conduction velocit ies, mechanical probing of hindlimb muscles, and local injection of ch emical stimulants (capsaicin and bradykinin). Five of the 15 group III fibers were stimulated by U46,619 (2-10 mu g injected into the abdomi nal aorta; mean baseline impulse frequency increasing from 7.3 (+/-3.2 ) impulses/s to 16.0 (+/-3.1)), while 7 of the 12 group IV fibers resp onded to U46,619 (impulse frequency increasing from 4.3 (+/-3.2) to 8. 8 (+/-3.6)). The average latency for the response (20-30 s) did not di ffer between the two groups of afferent fibers. We conclude that group III and IV afferent fibers originating from the skeletal muscle of th e hindlimb are stimulated by TxA(2) and that the release of TxA(2) in skeletal muscle could evoke cardiorespiratory reflexes known to be act ivated by stimulation of these afferent nerves.