Measurement of cerebral vascular extraction fractions in the rat using intracarotid injection techniques.

A small volume (5 microliters) common carotid arterial injection method is described for the quantitation of cerebral vascular extraction fractions (Et) of diffusion limited tracer molecules in the rat. The method is a modification of a technique introduced by Oldendorf and widely used for the study of blood-brain barrier phenomena. While the Oldendorf technique has proven valuable for estimating the relative permeabilities of substances, it is limited in measuring Et under conditions of physiologically or pharmacologically altered permeability or blood flow. The method described in this paper--using a small volume (5 microliters) common carotid injection, a freely diffusible reference tracer, [14C]butanol, and a 5 sec circulation time--allows for measurements of Et that reflect changes in blood flow and small differences in permeability. The modified method is important for the study of the regulation of cerebral vascular permeability and flow in an inexpensive animal model.