Analysis of tropalgin effects in an inflammation pain model in rats with different pain threshold

Abstract

Individual pain sensitivity of male Wistar rats was determined in a tail-flick model after action of focused thermal ray (flick) on tail. Rats with latency less than 5 sec were qualified as high sensitive (HS) to pain, more than 10 sec as low sensitive (LS) to pain. Effects of a new nonopioid analgetic tropalgin 2 mg/kg (ED50) i.p. was studied in both groups of rats. Tropalgin was effective as an analgetic in aseptic inflammation model (formaldehyde test). The analgetic effects of tropalgin were same as after administration of methamizol sodium (50 mg/kg) or diclofenac sodium (7 mg/kg). Tropalgin did not change individual pain sensitivity in both HS and LS rats without inflammation. In HS to pain rats, the common time of pain behavioral reactions was decreased by 53% in an acute phase of pain and by 58% in a tonic phase of pain in inflammation pain model. In LS to pain rats, the time of leaking of inflamed paw was decreased by 42% in the first phase and by 66% in the second phase. We suggest that analgetic effect of tropalgin is connected with adenosine release in purinergic neurons that has been demonstrated earlier for drugs of tropin structure.