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 Phyllant hus urinaria, P. tenellus, P, niruri and P. sellowianus have been inve stigated in several models of nociception in mice. The HE of four spec ies of Phyllanthus (1-90 mgkg(-1), i.p.) caused a dose-related inhibit ion of acetic acid-induced abdominal constriction in mice with ID50 va lues 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, t he 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, ho wever, more potent in relation to the second phase of the pain. The ID 50 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, res pectively, and percentages of maximal inhibition were 63 +/- 2, 70 +/- 2, 41 +/- 3 and 46 +/- 4, respectively. The ID50 values (mgkg(-1)) fo r 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 antinoc iceptive profile, but they were about one-tenth to one-twentieth as po tent when given intraperitoneally. However, the HEs of Phyllanthus fai led to affect formalin-induced paw oedema and did not interfere with t he 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 Phylla nthus. Furthermore, the HEs Phyllanthus in contrast to morphine had no analgesic effect in either tail-flick or hot-plate tests. Taken toget her, these findings confirm and extend our previous results and indica te that all studied HE of species of plant belonging to the genus phyl lanthus exhibit potent and long-lasting antinociceptive activity in se veral models of pain, including the neurogenic algesic component of th e formalin test. The mechanism underlying their analgesic profile is p resently unknown.