Local cerebral blood flow in the conscious rat as measured with 14C-antipyrine, 14C-iodoantipyrine and 3H-nicotine.

Abstract

Local cerebral blood flow (LCBF) in the conscious rat was estimated with 1 of 3 radiotracers, 14C-antipyrine, 14C-iodoantipyrine or 3H-nicotine. A tracer was infused i.v. at a constant rate and blood concentration was followed until the animal was killed by decapitation. Tracer concentration was then measured in 14 brain regions. The Kety-Schmidt analysis was applied to the data with 14C-antipyrine and 14C-iodoantipyrine. The results confirmed findings that 14C-iodoantipyrine provides LCBF that are twice those obtained with 14C-antipyrine and that LCBF found with an inert gas. LCBF was calculated from the 3H-nicotine data by assuming complete extraction of tracer from blood by brain. This assumption was approximated for infusion times of 50 s or less when LCBF derived with 3H-nicotine did not differ significantly from LCBF obtained with 14C-iodoantipyrine. The 50 s 3H-nicotine-derived flows for the pineal and pituitary glands were, respectively, 2.59 .+-. 0.36 (SEM [standard error of the mean]) cm3/g min-1 and 1.28 .+-. 0.08 cm3/g min-1. LCBF calculated for 70-240 s 3H-nicotine infusion were lower than 50 s values due to back-diffusion, but nevertheless were as high as 14C-antipyrine LCBF due to the marked binding of tracer by brain tissue. The results supported the conclusion that iodoantipyrine is the non-gaseous agent of choice for measuring LCBF precisely short infusion schedules with nicotine provided good estimates of LCBF.