The effect of lumbar sympathectomy on fiber composition, contractility of skeletal muscle and regulation of central circulation in dogs

It has been speculated upon that the sympathetic activity might be of significance for fiber composition in skeletal muscle and by similar features indirectly affecting muscle contractility and regulation of circulation. To further study this hypothesis unilateral lumbar sympathectomy from L-2 and down was applied on 5 female dogs. After 14 weeks the gracilis muscle on the sympathectomized and the control side as well were examined for their muscle fiber compositions, endurance capacity and how heart rate and blood pressure responses were affected. Muscle fiber composition decreased to 28% slow twitch fibers as compared to 41% on the control side (p less than 0.01). The relative cross-sectional area of the fast twitch fibers increased simultaneously from 57 (control side) to 71% (p less than 0.05). Endurance performance measured as contraction time at 50% of peak tension decreased from 55 to 29 s (p less than 0.05). On an individual bases including both control and sympathectomized muscles it was found that heart rate increased with percent fast twitch muscle fibers (p less than 0.01) and a tendency was present for a similar relationship between blood pressure and fiber types (p less than 0.1).