Absence of abundant saturable binding sites for halothane or isoflurane in rabbit brain: inhaled anesthetics obey Henry's law.

We tested whether the existence of saturable binding sites for anesthetics causes the solubility of halothane or isoflurane in rabbit brain not to obey Henry's law. For each anesthetic, we measured brain/gas partition coefficients (paired samples) at approximately 0.05 MAC and 5 MAC at 38.5 degrees C. In addition, for halothane, brain/gas partition coefficients (paired samples) were determined at 0.05 MAC and 2 MAC. The values for halothane at 0.05 MAC, 2 MAC, and 5 MAC did not differ; values for isoflurane at 0.05 MAC and 5 MAC did not differ. Over the range of anesthetic partial pressures studied, no evidence for saturable binding was found. We conclude that the solubility of halothane and isoflurane in brain is independent of the partial pressure applied; inhaled anesthetics obey Henry's law.