Autoradiographic method for quantitative evaluation of the blood-brain barrier effects of contrast media

Opening of the blood-brain barrier after intravenous injection of different contrast media has been investigated by a quantitative autoradiographic technique using 14C-aminoisobutyric acid (AIB) as the blood-brain barrier radiotracer. In this study, experiments were carried out in adult rats. Animals were injected intravenously with 2 ml/kg of the tested contrast medium, and immediately afterward with the blood-brain radiotracer AIB. The following contrast media have been tested: diatrizoate 38%, ioxithalamate 38%, ioxaglate 38%, the nonionic product metrizamide 40%, and a new nonionic product P-297, 400 mg l/ml. Control animals were injected intravenously with saline 0.9% (2 ml/kg) before the injection of the tracer. The degree of blood-brain barrier opening was quantitatively assessed by calculating the capillary rate constant for blood-to-brain transfer of AIB (ki) from the brain activity and the arterial integral for a 6 min experiment. Preliminary data seem to indicate that the intravenous injection of 2 ml/kg of a constant medium may produce a tiny opening of the blood-brain barrier. But, if this is so, this blood-brain barrier opening is of a very low magnitude in the normal brain and there are no obvious differences between the test contrast agents injected intravenously.