Increased capillary tortuosity and pericapillary basement membrane thinning in skeletal muscle of mice undergoing running wheel training.

To work out which microvascular remodeling processes occur in murine skeletal muscle during endurance exercise, we subjected C57BL/6 mice to voluntary running wheel training for 1 week (1 wk-t) or 6 weeks (6 wks-t). By means of morphometry, the capillarity as well as the compartmental and sub-compartmental structure of the capillaries were quantitatively described at the light microscopy level and at the electron microscopy level, respectively, in the plantaris (PLNT) muscle of the exercising mice in comparison to untrained littermates. In the early phase of the training (1 wk-t), angiogenesis [32% higher capillary/fiber (C/F) ratio; P<0.05] in PLNT muscle was accompanied by a tendency for capillary lumen enlargement (30%; P=0.06) and a reduction of the pericapillary basement membrane thickness [(CBMT) 12.7%; P=0.09] as well as a 21% shortening of intraluminal protrusion length (P<0.05), all compared with controls. After long-term training (6 wks-t), when the mice reached a steady state in running activity, additional angiogenesis (C/F ratio: 76%; P<0.05) and a 16.3% increase in capillary tortuosity (P<0.05) were established, accompanied by reversal of the lumen expansion (23%; P>0.05), further reduction of the CBMT (16.5%; P<0.05) and additional shortening of the intraluminal protrusion length (23%; P<0.05), all compared with controls. Other structural indicators, such as capillary profile sizes, profile area densities, perimeters of the capillary compartments and concentrations of endothelium-pericyte peg-socket junctions, were not significantly different between the mouse groups. Besides angiogenesis, increase of capillary tortuosity and reduction of CBMT represent the most striking microvascular remodeling processes in skeletal muscle of mice that undergo running wheel training.

Proteoglycans and collagen in the intervertebral disc of the rhesus monkey (Macaca mulatta).

The different varieties of supportive tissues in the intervertebral discs of the rhesus monkeys (Macaca mulatta) were investigated with regard to morphology of the collagen fibrils and distribution and localization of proteoglycans (PG). The annulus fibrosus and the nucleus pulposus of the intervertebral disc were structurally closely integrated into the cartilaginous endplates of the vertebral bodies. The collagen fibrils in the intervertebral disc fell into two categories; i.e. thick (70-110 nm) and thin (40-50 nm) ones. In the outer zone of the annulus fibrosus only thick fibrils occurred, while in the regions of the inner part of the annulus fibrosus, in the periphery of the nucleus pulposus and in the cartilaginous endplates both types of fibrils were found. PG were found free in the matrix and in great numbers in association with collagen fibrils in all regions of the intervertebral disc. They interconnected neighbouring fibrils and decorated the surface of the collagen fibrils in irregular orientation. Only the thick fibrils of the annulus fibrosus contained small regularly arranged intrafibrillar PG precipitates. The free precipitates were usually longer and thicker than the collagen-associated PG, in addition they could be branched. Since rhesus monkeys are closely related to humans, they can serve as model organisms and the findings presented may be of relevance to the understanding of the human intervertebral discs.