Time-Dependent Changes of Lumped and Rate Constants in the Deoxyglucose Method in Experimental Cerebral Ischemia

Abstract

Time-dependent changes in the lumped and rate constants in a bilateral middle cerebral artery (MCA) occlusion in cats were evaluated. These variables were measured in 11 cats after a sham operation, in five after a 1-h occlusion, in two after a 2-h occlusion, in five after a 4-h occlusion, and in four after a 16-h occlusion. The time course of the cerebral tissue radioactivity [C_i* ( t)] was monitored by external coincidence counting during a programmed infusion of [¹⁸F]2-fluorodeoxyglucose (FDG). Arterial plasma concentration [C_p* ( t)] of tracer was kept constant during the first 45 min. Comparison of k₂* and k₃* in the sham-operated group, estimated by external coincidence counting, and by the ratio of extraction fractions of glucose and [¹⁸F]2-FDG, demonstrated no significant difference between these rate constants in these two groups of animals. The rate and lumped constants were also estimated from C_i* ( t) and C_p* ( t), as well as from the ratio of extraction fractions of glucose and [¹⁸F]2-FDG, respectively, in the MCA occlusion group. Significant decrease in k₃* was observed after 1 h of occlusion (20% lower than in the sham operation, p < 0.05); in k_i* decrease occurred within 4 h of occlusion (21% lower than in the sham operation, p < 0.05). However, decrease in k₂* was observed only after 16 h of occlusion (26% lower than in the sham operation, p < 0.05). Namely, decrease of rate constants occurred first in k₃* then in k₁* and k₂*. In contrast to the rate constants where decrease was observed, a significant increase in the lumped constant occurred between 1 and 4 hours after occlusion (55% higher than in the 1-h occlusion, p < 0.05). However, the values of the lumped constant were not significantly different between the 4-h occlusion group and the 16-h occlusion group.