Probable role of spinal purinoceptors in the analgesic effect of Trigonella foenum (TFG) leaves extract

In our previous work, we demonstrated that Trigonella foenum (TFG) leaves extract can exert analgesic effects in both formalin (F.T.) and tail flick (T.F.) tests. Spinal serotonergic system, but not endogenous opioid system, was involved in TFG induced analgesia (in the second phase of formalin test). Some reports concern the similarity between NSAIDs and TFG extract in many pharmacological effects or the interaction between NSAIDs and purinergic system; so the present study was designed to investigate the relationship between TFG extract and purinergic system or the inhibition of cyclo-oxygenase (COX). We examined the effect of TFG extract on: (1) the response of rabbit platelets to ADP induced aggregation, (2) the contraction of mouse vas deferens induced by α,β-Me-ATP (a P2 receptor agonist; this receptor mediates the rapid phase of ADP- and ATP-evoked influx of Ca2+ through a non-specific cation channel in platelets), (3) α,β-Me-ATP induced hyperalgesia in tail flick test in male rats and (4) the specific inhibition of COX-1 and COX-2. Our results showed that TFG extract (0.5, 1, 1.5, 3 mg/ml) inhibited ADP (10−5 mol) induced platelet aggregation (IC50 = 1.28 mg/ml). α,β-Me-ATP (30 μM) induced isometric contraction in vas deferens while suramin (a P2 receptor antagonist, 50, 150, 300 μM) or TFG extract (0.5, 1, 2, 3 mg/ml) inhibited this effect significantly (IC50 were 91.07 μM and 1.57 mg/ml, respectively). Moreover, α,β-Me-ATP (3 μg/rat, i.t.) induced hyperalgesia in tail flick test, but it was prevented by co-injection of α,β-Me-ATP with suramin (120 μg/rat, i.t.) or TFG extract (1 mg/rat, i.t.). Effective concentrations of TFG extract in the above mentioned experiments did not inhibit COX enzymes in EIA tests. In conclusion, these results indicate that the blocking of spinal purinoceptors may contribute in the analgesic effect of TFG leaves extract.