[Site of action of analgesics: the peripheral site of action of these drugs].

This review describes: recent findings about the peripheral site of action and mechanism of the algesic action of narcotic and nonnarcotic analgesics. Special attention was given to the stimulatory or inhibitory actions of opiates and opioid peptides on the polymodal receptor of the sensory afferent fibers. Bradykinin, a pain producing substance, augmented the production of opioid peptides, for example, methionine and leucine enkephalins in in vitro and in vivo experiments. It was demonstrated that a pharmacological feed back reaction, the antinociceptive response, took place in the peripheral site of the primary afferent fibers.