Coronary vascular smooth muscle responses to swimming challenges in juvenile salmonid fish

Using ( 3 H)thymidine to measure the mitotic activity of medial vascular smooth muscle (VSM) from salmonid coronary arteries, we tested the hypothesis that periodic anaerobic swimming induces greater VSM mitotic activity than sustained aerobic swimming. Juvenile chinook salmon were swum either at a submaximal speed of 1.5 body lengths/s for 8 months alone, or at a combination of forced swims to exhaustion (critical swimming speed) on alternate days in addition to a continuous low speed of 0.5 body lengths/s for 3 months. Fish swum at a continuous low speed (0.5 body lengths/s) for either 3 or 8 months acted as controls. Rainbow trout were forced to burst swim to exhaustion twice daily for 3 days. Mitotic activity in coronary arterial explants was measured at the end of each of the regimes using ( 3 H)thymidine. Compared with controls, the combination of exhaustive swimming on alternate days and continuous submaximal swimming at 1.5 body lengths/s stimulated coronary VSM mitosis. Neither submaximal swimming alone nor burst swimming stimulated coronary VSM mitosis. We conclude that some but not all forms of periodic anaerobic swimming induce coronary VSM mitosis, with the duration and number of swimming events likely being important considerations.

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