Temperature and angiogenesis: the possible role of mechanical factors in capillary growth

This review examines the effect of prolonged cold exposure on muscle capillary supply in mammals and fishes. In rats and hamsters, the response to a simulated onset of winter is to conserve the microcirculation and maintain a constant capillary to fibre ratio (C:F), implying either an unaltered vacular bed or angiogenesis matched by muscle hyperplasia, while chronic acclimation to low environmental temperature induces a variable degree of muscle atrophy, which in turn increases capillary density (CD). In striped bass and rainbow trout, cold-induced angiogenesis results in an increase in C:F, but also a cold-induced fibre hypertrophy that is accompanied by a powerful angiogenic response such that CD is much less sensitive to changes in fibre size. Endothelial cells can act as mechanotransducers such that angiogenesis may be initiated by changes in their physical environment. It is hypothesised that in mammals, the metabolic consequences of cold exposure increases the luminal shear stress, while in fishes the stimulus for angiogenesis is abluminal stretch following an increase in fibre size.