Measurement of local cerebral blood flow with iodo [14C] antipyrine

TLDR

The autoradiographic diffusible tracer technique for measuring local cerebral blood flow was originally designed for the radioactive inert gas 131I‑labeled trifluoroiodomethane and requires tracers that diffuse freely across the blood‑brain barrier. The study sought a suitable nonvolatile tracer to replace gaseous tracers, leading to the development of iodo [14C]antipyrine, an analog with higher partition coefficients that should diffuse more freely through the barrier. Iodo [14C]antipyrine was selected because its higher partition coefficient between nonpolar solvents and water suggests enhanced diffusion across the blood‑brain barrier compared to [14C]antipyrine. When used in the local blood flow technique, iodo [14C]antipyrine produced values considerably higher than those obtained with [14C]antipyrine and essentially identical to the gas tracer, demonstrating it as a satisfactory nonvolatile tracer.

Abstract

The autoradiographic diffusible tracer technique for the measurement of local cerebral blood flow was originally designed for use with the radioactive, inert gas 131I-labeled trifluoroiodomethane and is applicable only with tracers that exhibit unrestricted diffusion through the blood-brain barrier. Because of the technical problems associated with the use of gaseous tracers, a suitable nonvolatile tracer has been sought. [14C] Antipyrine has been used previously and found to be unsuitable because of limitations in its diffusion through the blood-brain barrier. An analogue of [14C]antipyrine, iodo [14C]antipyrine, exhibits higher partition coefficients than [14C]antipyrine between nonpolar solvents and water and might, therefore, be expected to diffuse more freely through the barrier. Its use as the tracer in the local blood flow technique leads to values considerably above those obtained with [14C]antipyrine in the rat and cat and essentially the same as those obtained with the gas trifluoro[131I]iodomethane in the cat. Iodo[14C]antipyrine appears, therefore, to be a satisfactory nonvolatile tracer for the measurement of local cerebral blood flow.