Vocalization response to close-arterial injection of bradykinin and other algesic agents in guinea pigs and its application to quantitative assessment of analgesic agents.

A method for determining the vocalization response to algesic agents in conscious guinea pigs is described. Retrograde injection of small amounts of algesic agents into the femoral artery caused transient but obvious vocalization response in a dose-dependent manner. The vocal sound was converted into electrical signals and the envelope of the sound obtained by a peak detector circuit was recorded on an ink-writing oscillograph. The area of the vocalization response circumscribed by a base line and the envelope tracing of the vocal sound was also recorded. Bradykinin, kallidin, acetylcholine (ACh) and nicotine caused the vocalization response, while substance P, histamine, bethanechol, methacholine, serotonin, kallikrein and prostaglandins E1 and E2 caused no or little response. No detectable tachyphylaxis to bradykinin, ACh and nicotine was observed. The pretreatment with hexamethonium abolished the response induced by ACh or nicotine but not the response induced by bradykinin. These results suggest that the paravascular pain receptor of the femoral artery excited by ACh is nicotinic in character. Subcutaneous injection of morphine, pentazocine, diclofenac and aminopyrine inhibited the vocalization response induced by bradykinin in a dose-dependent manner.