The potency of fluorinated ether anesthetics correlates with their 19F spin-spin relaxation times in brain tissue

In this study, four fluorinated ether anesthetics and one non-anesthetic fluorinated alkane were observed in rat brain and adipose tissue using 19F-NMR spectroscopy. Measurements of 19F spin-spin relaxation times (T2) of the anesthetics in brain revealed T2 values (0.5-4.5 msec) that correlated linearly with the anesthetic potency (ED50) of the drugs. The non-anesthetic was present at very low concentrations in brain and had a T2 value (18.5 msec) far longer than that of any of the anesthetics. All of the drugs were present at high concentration in peripheral adipose tissue. 19F T2 values for these drugs in adipose tissue (200-400 msec) were far larger than the values observed in brain and did not correlate with anesthetic potency. These results indicate that volatile anesthetic molecules have a specific affinity for neural tissue and that immobilization of anesthetic molecules in brain correlates with anesthetic potency. The results with adipose tissue suggest that the interaction of anesthetic with brain tissue cannot be explained by a simple partition of these drugs into lipid.