Measurement of local cerebral blood flow with iodo 14C antipyrine

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 14Cantipyrine, iodo 14Cantipyrine, exhibits higher partition coefficients than 14Cantipyrine 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 14Cantipyrine in the rat and cat and essentially the same as those obtained with the gas trifluoro131Iiodomethane in the cat. Iodo14Cantipyrine appears, therefore, to be a satisfactory nonvolatile tracer for the measurement of local cerebral blood flow.