CHRONIC HYPOXIA AFFECTS CAPILLARY DENSITY AND GEOMETRY IN PIGEON PECTORALIS-MUSCLE

We examined fiber capillarization and ultrastructure in pectoralis mus cle of 11 pigeons (Columba livia; body mass, 603 +/- 12 (SE) g) i.e. n ine birds kept at 3800 m for 5 months (three in a small aviary (Al) an d five in smaller cages, A2) compared to three sea-level (SL) controls . There was no difference between groups in either the relative area o r number of aerobic and glycolytic fibers per total fibers, fiber size or mitochondrial volume density. Hematocrit was significantly greater in Al and A2 (59 +/- 1%) than SL (50 +/- 2%). In Al, capillary densit y relative to the sectional area of aerobic/total fibers, capillary di ameter and the contribution of tortuosity and branching to capillary l ength were significantly greater than Si,, yielding greater capillary length and surface area per volume of fiber. Capillary length and surf ace densities very close to those in Al and significantly greater than SL for the relative sectional area of aerobic/total fibers were also found in four out of five A2 birds, without alteration in capillary ge ometry or diameter. The size of the capillary-fiber interface (i.e. ca pillary-to-fiber surface ratio) in aerobic fibers was also greater in Al and A2 than Si,, indicating a greater capacity for oxygen supply of the muscle fibers in the altitude groups. (C) 1997 Elsevier Science B .V.