Cerebral blood flow in rats during physiological and humoral stimuli

The technique for estimating cerebral blood flow (CBF) in anesthetized rats by injecting 133Xe into the internal carotid artery represents a potentially useful and inexpensive model for screening cerebral vascular responses to pathophysiological and pharmacological stimuli. We have examined associated neuropathology, the validity and the reproducibility of the method, and made comparisons of initial slope estimates of CBF with those obtained by stochastic analysis. Initial slope estimates (CBF = 1.62 +/- 0.04 ml min-1g-1, X +/- SE, N = 38) were linearly related to stochastic measurements (CBF = 1.42 +/- 0.09 ml min-1g-1, N = 6), and overestimated mean CBF by about 15%. A reactivity to CO2 of 0.05 ml min-1g-1 per mm Hg, and an auto-regulation range of 70 to 180 mm Hg were found. CBF responses to the intra-arterial infusion of aminergic drugs were determined before and after opening of the blood-brain barrier with hypertonic urea. Serotonin reduced CBF after, but not before, the administration of urea. Acetylcholine increased CBF when the barrier was intact, the effect being augmented when the barrier was disrupted; these responses were reduced by atropine. Histamine increased CBF only after barrier opening, and this response was attenuated by the H2-receptor antagonist, metiamide. These studies indicate that initial slope estimates of CBF derived in rats from intracarotid 133Xe injection, which represents an inexpensive and simplified approach for screening cerebral circulatory adjustments, may facilitate the characterization of stimuli affecting CBF.