Nociceptive and edematogenic responses elicited by a crude bristle extract of Lonomia obliqua caterpillars.

Lyophilized Lonomia obliqua crude bristle extract (LOCBE) diluted in physiological saline (15, 35 and 50 microg of protein/paw) was injected in the plantar surface of the hind paw of the rat, causing a nociceptive response which lasted from 30 to a maximum of 50 min, peaking in the first 5 min. The animals also presented hematuria and nasal bleeding. Nociception was inhibited by indomethacin pretreatment (2.5 mg/kg, i.p., 60 min before), but not by guanethidine (30 mg/kg/day, s.c., for 3 days) or loratadine (5 mg/kg, p.o., 60 min before). LOCBE injection also produced paw edema peaking 1 h after injection and lasting for 6 h. Loratadine pretreatment, but neither guanethidine nor indomethacin, reduced edema. After the period of overt nociception, a nociceptive aftersensation response could be evoked up to 6 h after by immersing the paw into cold water (15 degrees C) for 10 s. Capsaicin (1.6 microg), formalin (0.5%) or prostaglandin E(2) (500 ng) did not produce the same aftersensation phenomenon. These results suggest that LOCBE-induced nociception is largely facilitated by prostaglandin production, and edematogenic response seems to be facilitated by prostanoids and histamine. Finally, LOCBE induced a state of sensitization to cold, which seemed to be specific as it was not caused by other noxious chemicals.