Capillary tortuosity in skeletal muscles of mammals depends on muscle contraction.

The study explores the relationship between capillary tortuosity (twisting or curving of capillaries, the smallest blood vessels in the body) in skeletal muscle tissues of various mammalian species and muscle contraction. They find that capillary orientation changes in response to muscle fiber shortening and is not linked to the size of the organism, its athletic ability, or aerobic capacity.

Study Design and Methodology

• The research worked on hindlimb muscles of different mammals, namely dog, goat, pony, and calf. The variety in size and aerobic capacity of these creatures helped facilitate a comprehensive study.
• All muscle specimens underwent a fixation through vascular perfusion – a process of preserving tissues by injecting a fixative solution into their blood vessels – at different sarcomere (basic unit of a muscle) lengths.
• The capillary count per fiber cross-section was estimated at two different section sets (0 and 90 degrees to the muscle fiber axis). This measure enabled the calculation of the capillary anisotropy and the coefficient c(K,0).

Findings

• The orientation of capillaries was found to decrease significantly with the shortening of muscle fibers.
• In muscles fixed at sarcomere lengths of 2.69 microns (dog vastus intermedius) and 1.52 microns (dog gastrocnemius), capillary tortuosity and branching increased capillary length density by 7% and 64% respectively.
• The findings were consistent with prior research involving the study of capillary anisotropy and sarcomere length in extended vs. contracted rat muscles.

Conclusion

• The study concludes that capillary anisotropy in mammalian skeletal muscles is related to sarcomere length in a curvilinear manner.
• There is no discernible systematic difference in capillary tortuosity based on body size, athletic ability, or aerobic capacity of the examined mammals.
• Importantly, it is established that capillary tortuosity is a consequence of fiber shortening, and is not an indicator of the oxygen requirements of the muscle tissue.