Algesiogenic and analgesic activities of synthetic substance P

The objective of our study was to determine whether the pure synthetic substance P(SP) is algesiogenic or analgesic when administered centrally or peripherally. The relationships between SP-induced analgesia and the content of morphine-like factor (MLF) in the brain were also studied. Intracarotid arterial administration of SP (20-200 microgram) produced no pseudoaffective responses to pain in six out of nine rats, but in the remaining three, there was an exhibition of these responses. Chlorpheniramine pretreatment antagonized these responses. On cantharidin blister base experiments in humans, SP (10(-3) g/ml) produced slight pain and an itchy sensation. SP given intracerebroventricularly produced an analgesia in mice in a dose of 5 ng/mouse, as determined by the acetic acid-induced writhing and hot plate methods. These SP-induced analgesia were antagonized by naloxone pretreatment. SP did not alter the content of MLF in the mouse whole brain. However, SP5-11 not only produced an analgesia but also increased the content of MLF. These results suggest that SP has a slight algesiogenic activity which might be mediated by histamine and a slight analgesic activity which might be mediated by MLF.