A study of capillaries in equine skeletal muscle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Anatomy and Physiology at Massey University

Abstract

Four horses of varying ages, breeds and sex were used to evaluate the variation in capillary supply and fibre type proportions in a range of equine skeletal muscles. A total of 100 muscles were sampled from the four horses. These samples were stained for myosin ATPase activity from which fibres were classified as ATPase low or ATPase high. Visualisation of capillaries was also achieved by the use of this stain. The 100 muscle samples were assessed for capillary/fibre ratio and for capillary density. From these muscles, 22 were chosen for more detailed analysis on the number of capillaries surrounding each fibre and the fibre area for ATPase low and ATPase high fibres individually. Fibre type distribution was found to vary from 0% to 100% ATPase low fibres and therefore a complete range of muscle fibre type proportions were obtained. An extensive range was found within a muscle or between adjacent muscles. There was no significant difference in mean fibre area between the two fibre types in the muscles examined. The percentage of ATPase low fibres and capillary/fibre ratio showed a significant regression (regression coefficient = 0.36, p < 0.05) For both the ATPase low fibres and the ATPase high fibres, larger fibres were surrounded by more capillaries. It was concluded that, although fibre size is the primary determinant for capillary supply, the contractile properties of the muscle in which a fibre is found will also determine the number of capillaries it should have at its disposal.