In vitro release of substance P from spinal cord slices by capsaicin congeners.

The in vitro release of immunoreactive substance P (I-SP) by capsaicin and three congeners was studied on slices of rat spinal cord upper dorsal horn. Capsaicin and its congeners were all able to stimulate I-SP release, indicating that they act on chemosensitive primary afferents terminating in this region. A positive correlation was found between the I-SP releasing and pain-producing potencies of these compounds. This is in agreement with the concept that primary afferents containing substance P (SP) are involved in the transmission of nociceptive information.