EVIDENCE THAT HETEROGENEITY OF CEREBRAL BLOOD-FLOW DOES NOT INVOLVE VASCULAR RECRUITMENT

Recent studies indicate that blood flow to cerebral cortex is not homo geneous but may vary both spatially and temporally. In addition, some investigators have reported that capillaries and arterioles can be rec ruited to increase cerebral blood flow, an issue that is extremely con troversial. The goal of this study was to determine whether recruitmen t of cerebral blood vessels is an important mechanism in spatial and t emporal heterogeneity of cerebral blood flow. In seven anesthetized ve ntilated rats, different fluorescent tracers were injected 45 and 10 s before decapitation. In addition, [C-14]iodoantipyrine also was injec ted 10 s before decapitation. After the brains were sectioned, fields in the cerebral cortex were examined microscopically for fluorescence and processed for measurement of cerebral blood flow with techniques o f quantitative autoradiography and image analysis. With examination of 24 +/- 2 (SE) points in cerebral cortex of each rat, similar numbers of small blood vessels (less-than-or-equal-to 10 mum) were counted tha t contained fluorescent tracers injected 45 and 10 s before decapitati on (346 +/- 48 and 355 +/- 42 vessels/mm2, respectively; P > 0.05). La rge blood vessels (20-60 mum; 73 +/- 6 vessels in each rat) contained both fluorescent tracers. In addition, adjacent regions of high and lo w blood flow contained similar numbers of small and large vessels. Our findings indicate that vascular recruitment is not an important mecha nism in temporal or spatial heterogeneity of cerebral blood flow.