Effects of aspirin and morphine on the release of a bradykinin-like substance into the subcutaneous perfusate of the rat paw.

The effects of aspirin and morphine on the release of bradykinin-like substance into the substaneous perfusate following various noxious stimuli were investigated in rat paw preparation. Subcutaneous perfusion was performed with saline or with saline containing o-phenanthroline or soy bean trypsin inhibitor at a rate of 3--4 drops/min. Ten drops per fraction were assayed for bradykinin activity. Pressure on the instep, application of heat to the foot and stimulation of the sciatic nerve were employed as noxious stimuli. Aspirin (200 mg/kg i.p.) inhibited the release of bradykinin due to heat, pressure and sciatic nerve stimulation, while morphine (5 mg/kg i.m.) inhibited only the release of bradykinin due to sciatic nerve stimulation. Results suggest that analgesics, such as aspirin and morphine, have a depressant action on pain by inhibiting the release of bradykinin locally. They also suggest that aspirin inhibits the release of bradykinin regardless of the type of noxious stimuli, while morphine inhibits the release of bradykinin which is mediated by neural mechanisms.