Effects of hypoxia on capillary orientation in anterior tibialis muscle of highly active mice.

The plasticity of capillary orientation in response to combined hypoxic hypoxia and high activity levels was investigated in anterior tibialis muscle of Japanese waltzing mice (Mus wagneri rotans). Following 2 weeks of normobaric, normothermic hypoxia (PIO2 congruent to 87 Torr), muscles were perfusion-fixed in situ with glutaraldehyde and analyzed morphometrically. Muscles from hypoxic waltzers, HW, were compared with those from normoxic waltzers, NW, and normoxic control mice, N. At sarcomere lengths from 2.84 to 1.69 microns, tortuosity and branching increased capillary length 3 to 38%. When capillary orientation was related to sarcomere length, muscles from HW were not different from NW or N. At group-averaged sarcomere lengths of 2.22 microns (HW), 2.33 microns (NW) and 2.35 microns (N), tortuosity and branching contributed 16,20 and 18% respectively, to capillary length. We conclude that high activity levels under normoxic or hypoxic conditions in Japanese waltzing mice do not augment muscle capillary length by means of increased capillary tortuosity and/or branching.