Functional capillary density in skeletal muscle during vasodilation induced by isoprenaline and muscular exercise

Abstract

Functional capillary density in skeletal muscle was studied in an isolated, autoperfused preparation of the abdominal muscles of the rat during different forms of vasodilation. The macromolecule hydroxyethyl starch (MW 450,000), labeled with the fluorochrome lissamine-rhodamine B 200, was intravenously injected. When a certain volume of blood had passed the muscle the tissue was fixed by snap freezing. In histological sections those capillaries which had been perfused by the dye could be visualized in the fluorescence microscope. Increase in total muscular blood flow, measured by arterial drop counting, was induced by intraarterial infusion of isoprenaline and by muscular work (control 30.0 ± 2.6, isoprenaline 48.2 ± 4.4, postcontraction hyperemia 44.2 ± 7.4 ml/min × 100 g). During hyperemia the functional capillary density (stained capillaries per muscle fiber) was affected in a different way: 0.81 ± 0.02 control, 0.71 ± 0.03 isoprenaline, and 0.93 ± 0.04 postcontraction hyperemia. The data support the view that a rise in total blood flow is not necessarily associated with an increase in functional capillary density.