Effects of morphine and acetylsalicylic acid on kinin forming enzyme in rat paw.

Coaxial perfusion was carried out in the rat paw; pinching the instep of the foot and electrical stimulation of the sciatic nerve caused an increase in the release of a bradykinin-like substance and kinin forming enzyme into the perfusate. Release of the latter was noted with pinching even independently of the release of the bradykinin-like substance. Acetylsalicylic acid (200 mg/kg i.p.) inhibited the release of kinin forming enzyme due to pinching or to sciatic nerve stimulation, while morphine (5 mg/kg i.m.) inhibited only the release of the enzyme due to sciatic nerve stimulation. Our results suggest that production of localized pain may be largely due to the activity of the released kinin forming enzyme and the bradykinin-like substance. In addition, the mechanism of inhibition by morphine on release of kinin forming enzyme appears to differ from that of acetylsalicylic acid.