Lithium-induced hyperpolarization of the human rectum in vivo.

The transmucosal potential difference across the rectal mucosa was measured in 30 healthy subjects and in 13 psychiatric patients on lithium treatment for manic-depressive psychosis. It was significantly greater in the lithium-treated patients. A highly significant correlation was found between the potential difference and the serum lithium, and in all eight patients in whom it was measured before and one week after starting lithium treatment a rising potential difference was found. This phenomenon may possibly be explained in terms of resistance of the rectal mucosa to vasopressin.