Mice with a melanocortin 1 receptor mutation have a slightly greater minimum alveolar concentration than control mice.

ANESTHESIA folklore includes a perception that patients with red hair have a greater MAC (the minimum alveolar concentration of anesthetic that prevents movement in response to noxious stimuli in 50% of subjects). In support of this perception, Liem et al. found that a greater concentration of the inhaled anesthetic desflurane was required to suppress movement in response to intense electrical stimulation in red haired humans. Such a finding has obvious clinical implications. In addition, a determination of the underlying cause might provide some insight into the mechanisms by which inhaled anesthetics act. Loss of function mutations in the melanocortin 1 receptor (MC1R) gene account for the majority of cases of red hair in humans. Mice with a melanocortin 1 receptor mutation (MC1R) resulting in a nonfunctional receptor have a yellow coat. These observations suggested the hypothesis that MC1R mice have greater MAC values than control mice. Accordingly, we determined desflurane, isoflurane, halothane, and sevoflurane MAC values for both MC1R and control mice.