Abstract
1. A material that powerfully inhibits the bovine retractor penis and rat anococcygeus muscles has been extracted from these muscles. The inhibitory activity is unaffected by atropine 10(-6) M, phentolamine 5 x 10(-6) M or propranolol 5 x 10(-6) M. 2. This inhibitory material exists in two forms, a stable but inactive form and an unstable inhibitory form. As isolated the material is in the stable, inactive form and is converted into the active form by a brief exposure to acid. The optimum for conversion is pH 2.0 and the active form, after neutralization, reverts with time to the inactive but can be reactivated by a further exposure to acid. The reversion to the inactive form is temperature sensitive, and is rapid at 37 degrees C. 3. The inhibitory material, both active and inactive, is irreversibly destroyed by 2 min in a boiling water bath or by exposure to U.V. irradiation. 4. The inhibitory material is not confined to tissues known to possess a non-adrenergic non-cholinergic innervation. Similar activity has been detected in extracts os skeletal and cardiac muscle and of the liver. The poorly innervated rat uterus and the non-innervated human umbilical artery, however, gave only small and variable amounts. The possible relationship of this material to non-adrenergic non-cholinergic nerves is discussed.