Interdependency of local capillary density, blood flow, and metabolism in rat brains

Previous investigations have established a strong correlation between local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU). In the present study the relationship between density of perfused brain capillaries and LCBF or LCGU was investigated in conscious and anesthetized rats. Perfused capillaries were stained by labeling the plasma with the gamma globulin-coupled fluorochromes, fluorescein isothiocyanate (FITC) and lissamine-rhodamine B 200 (RB 200). The density of perfused capillaries was determined in 12 different brain structures by fluorescence microscopy of embedded brain sections following coronal sectioning in a cryostat. Significant differences were found among brain structures investigated; the lowest density of perfused capillaries was found in the white matter (e.g., corpus callosum 162 fragments/mm2), whereas the highest values were determined in the structures of the auditory system (e.g., inferior colliculus 810 fragments/mm2). LCBF and LCGU were measured in two separate groups of rats using standard autoradiographic methods. In all three experimental groups, the same structures were identified and measured with a high degree of accuracy and local resolution. Density of perfused capillaries correlated well with LCBF (r = 0.93) and even better with LCGU (r = 0.97). In addition to the relationship between LCGU and LCBF established by earlier studies, these data show the intimate interrelationship between LCGU, density of perfused capillaries, and LCBF.