S. Egginton et al., Differential effects of cold exposure on muscle fibre composition and capillary supply in hibernator and non-hibernator rodents, EXP PHYSIOL, 86(5), 2001, pp. 629-639
Changes in the composition of fibre types and the capillary supply of skele
tal muscle (tibialis anterior) were quantified in rats and hamsters subject
ed to 8-10 weeks of cold exposure and reduced photoperiod (10 degreesC, 1 h
light-23 h dark). Muscle mass decreased in both species (by 12% and 17%, r
espectively). 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 H, but not Type I fibres. In rat muscle ther
e was little difference between the two groups in average capillary to fibr
e 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 +/- 0.1
1, 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 gly
colytic cortex and angiogenesis in the oxidative core. Following acclimatio
n of rats to cold there was a reduction in the supply area of individual ve
ssels (capillary domain), particularly in the cortex (9310, N; 8938 mum(2),
H; P < 0.05). In contrast, hypothermic hamsters showed only a small decrea
se in mean domain area in the cortex (948 mum(2), N; 846 mum(2), H; n.s.) b
ut a marked reduction in the core (871 mum(2), N; 604 mum(2), H; P < 0.01).
Rats showed little or no change in local capillary supply (LC-FR) to fast
fibres on acclimation to cold, while in hamsters the LCFR of Type fib fibre
s showed a decrease in the cortex (2.7, NT, 2.3, H) and an increase in the
core (3.0, N; 3.3, H) during acclimation to cold. These data suggest that d
uring a simulated onset of winter rats maintain FCSA and capillary supply a
s part of an avoidance strategy, whereas hamsters increase muscle capillari
ty in part as a consequence of disuse atrophy.