Static contraction of hindlimb muscles in cats reflexly relaxes tracheal smooth muscle

Static contraction of skeletal muscle is associated with increased ventilation. Although chemical stimulation of afferents from skeletal muscle causes relaxation of tracheal smooth muscle, it is not known if skeletal muscle contraction also causes tracheal relaxation. Therefore, in 10 chloralose-anesthetized cats, I examined the hemodynamic and tracheal smooth muscle responses to hindlimb skeletal muscle contraction induced by stimulating the L7 and S1 ventral roots. Isometric tension was measured in the transverse cervical trachea. During contraction average gastrocnemius tension increased from 0.7 +/- 0.1 to 4.9 +/- 0.6 kg, blood pressure and heart rate increased from 100 +/- 8 to 128 +/- 9 mmHg and from 192 +/- 11 to 202 +/- 13 beats/min, respectively, whereas tracheal tension decreased from 19.7 +/- 0.4 to 17.5 +/- 0.7 g (all P less than 0.02). There were significant (P less than 0.01) linear correlations between change in tracheal tension and maximal developed tension (r = -0.65), tension time (r = -0.68), and average developed tension (r = -0.76). Transection of the L7 and S1 dorsal roots in six cats reduced the tracheal relaxation associated with muscle contraction (pre: 19.9 +/- 0.3 to 17.5 +/- 0.3 g vs. post: 20.3 +/- 0.4 to 20.3 +/- 0.6 g) while average developed gastrocnemius muscle tension was not altered (pre: 1.1 +/- 0.1 to 6.4 +/- 1.1 kg vs. post: 1.2 +/- 0.2 to 6.8 +/- 1.2 kg). Thus static contraction of hindlimb muscles in cats reflexly lowers tracheal tension. This response is related to muscle mass and total tension generated by the contracting skeletal muscle.