Differential effects of cold exposure on muscle fibre composition and capillary supply in hibernator and non-hibernator rodents
|S. Egginton a1, J. Fairney a1 and J. Bratcher a1|
a1 Angiogenesis Research Group, Department of Physiology, University of Birmingham Medical School, Birmingham B15 2TT, UK
Changes in the composition of fibre types and the capillary supply of skeletal muscle (tibialis anterior) were quantified in rats and hamsters subjected to 8-10 weeks of cold exposure and reduced photoperiod (10 °C, 1 h light-23 h dark). Muscle mass decreased in both species (by 12 % and 17 %, respectively). Following acclimation to cold there were no specific changes in fibre cross-sectional area (FCSA) in rats, whereas in hamsters there was a substantial atrophy of Type II, but not Type I fibres. In rat muscle there was little difference between the two groups in average capillary to fibre ratio (C:F) (1.76 ± 0.15, normothermia, N; 1.69 ± 0.05, hypothermia, H) and average capillary density (CD) (188 ± 14 mm-2, N; 201 ± 12 mm-2, H). Similarly, the average C:F was unaltered in hamsters (2.75 ± 0.11, N; 2.72 ± 0.15, H), although the 30 % smaller fibre size observed with hypothermia resulted in a corresponding increase in average CD, to 1539 ± 80 mm-2 (P < 0.01). However, there was a coordinated regional adaptation to cold exposure in hamsters resulting in capillary rarefaction in the glycolytic cortex and angiogenesis in the oxidative core. Following acclimation of rats to cold there was a reduction in the supply area of individual vessels (capillary domain), particularly in the cortex (9310, N; 8938 µm2, H; P < 0.05). In contrast, hypothermic hamsters showed only a small decrease in mean domain area in the cortex (948 µm2, N; 846 µm2, H; n.s.) but a marked reduction in the core (871 µm2, N; 604 µm2, H; P < 0.01). Rats showed little or no change in local capillary supply (LCFR) to fast fibres on acclimation to cold, while in hamsters the LCFR of Type IIb fibres showed a decrease in the cortex (2.7, N; 2.3, H) and an increase in the core (3.0, N; 3.3, H) during acclimation to cold. These data suggest that during a simulated onset of winter rats maintain FCSA and capillary supply as part of an avoidance strategy, whereas hamsters increase muscle capillarity in part as a consequence of disuse atrophy. Experimental Physiology (2001) 86.5, 629-639.
(Received May 14 2001)
(Accepted June 20 2001)