Spatial distribution of nutritive and nonnutritive vascular routes in perfused rat hindlimb muscle using microspheres

Skeletal muscle appears to have two vascular flow routes, nutritive and non nutritive, where the balance of flow is controlled by vasoconstrictors. In the present study, spatial distributions of the two flow routes in muscles of the perfused rat hindlimb were attempted using fluorescent microspheres (15 mum in diameter). Microspheres were injected during steady-state perfus ion with norepinephrine (proposed recruiter of nutritive flow), serotonin ( proposed recruiter of nonnutritive flow), or vehicle. The three-dimensional location of individual microspheres in representative muscles was determin ed using a Fluorescent Imaging CryoMicrotome. Norepinephrine and serotonin each increased perfusion pressure (P < 0.05) but stimulated and inhibited o xygen consumption (P < 0.05), respectively. The distribution of microsphere s lodged in muscle was independent of the agent used. Spatial perfusion ind ices for norepinephrine, serotonin, and vehicle did not differ from each ot her. Similarly, there was no difference in these indices for a theoretical distribution where microspheres were deliberately positioned in muscle bund le capillaries or interfibrillar connective tissue vessels. We conclude tha t the nutritive and nonnutritive flow routes are distributed throughout mus cle sections consistent with their locations in muscle bundle capillaries a nd interfibrillar connective tissue, respectively, (C) 2000 Academic Press.