FURTHER-STUDIES ON THE ANTINOCICEPTIVE ACTION OF THE HYDROALCOHOLIC EXTRACTS FROM PLANTS OF THE GENUS PHYLLANTHUS

The analgesic effects of the hydroalcoholic extracts (HEs) of Phyllanthus urinaria, P. tenellus, P, niruri and P. sellowianus have been investigated in several models of nociception in mice. The HE of four species of Phyllanthus (1-90 mgkg(-1), i.p.) caused a dose-related inhibition of acetic acid-induced abdominal constriction in mice with ID50 values of 5.4, 8.5, 18.2 and 53.0 mgkg(-1) and maximal inhibition (%) of 80 +/- 2, 67 +/- 8, 63 +/- 8 and 50 +/- 4 for P. urinaria, P. niruri, P. tenellus and P. sellowianus, respectively. In the formalin test, the HE of all Phyllanthus species (0.3-60 mgkg(-1), i.p.) caused graded inhibition of both phases of formalin-induced pain, but they were, however, more potent in relation to the second phase of the pain. The ID50 values (mgkg(-1)) for the first phase were 20.0, 23.0, > 60, and > 60 for the P. urinoria, P. tenellus, P. niruri and P. sellowianus, respectively, and percentages of maximal inhibition were 63 +/- 2, 70 +/- 2, 41 +/- 3 and 46 +/- 4, respectively. The ID50 values (mgkg(-1)) for the second phase were 0.71, 4.87, 7.7, 33.0, with maximal inhibition (%) of 91 +/- 6, 97 +/- 3, 97 +/- 3 and 92 +/- 6, respectively. Given orally the HEs of species of Phyllanthus caused a significant antinociceptive profile, but they were about one-tenth to one-twentieth as potent when given intraperitoneally. However, the HEs of Phyllanthus failed to affect formalin-induced paw oedema and did not interfere with the performance of animals in the rota-rod test. Naloxone (5 mgkg(-1)) completely reversed the analgesic effect caused by morphine (5 mgkg(-1)), but had no effect against the analgesic effect of the HE of Phyllanthus. Furthermore, the HEs Phyllanthus in contrast to morphine had no analgesic effect in either tail-flick or hot-plate tests. Taken together, these findings confirm and extend our previous results and indicate that all studied HE of species of plant belonging to the genus phyllanthus exhibit potent and long-lasting antinociceptive activity in several models of pain, including the neurogenic algesic component of the formalin test. The mechanism underlying their analgesic profile is presently unknown.