Indian Journal of Experimental Biology Vol. 40 , November 2002 , pp . 1314-1316 Anti-nociceptive effect of synthesized di-hydroxy flavones: Possible lnechanism K Girija*, M Kannappa Reddy & S Viswanathan** *College of Pharmacy , Mother There sa Institute of Health Sciences , Pondicherry, India and Medicinal Ch emistry Re search Centre, Institute of Pharmac ology, Madra s Medical Coll ege, Chennai 60000 3, India Received 4 March 2002; revised 30 May 2002 Renewed interest on the research on the fl avonoids is gaining more importance. Earlier literature on fla vonoid s indicated a significant anti-nociceptive action for tlavon es and mono-substituted fl avone s. However, they exhibited a ceiling effect. The present study was undertaken by new synthesiz in g s ix disubstituted flavones (DHFs) since poly s ubstituted on es are expected to produce more potent effect. Their anti-nociceptive eff e ct and the rol e of opioid involveme nt were studied using acetic acid induced abdominal constriction assay. All the six DHFs administered in elicited a dose related inhibition of abdominal con strictions indicating th e presence of the anti-no ciceptive response. Ho we ver, these sub stances also showed a similar ceiling effect. Like other flavonoid substances, they also utilized opioid pathways. It is sugges ted th at these newly synthesized DHFs can be included along with other nav ono id s while attempting clinical trial for analgesic use. Flavonoids have been extensively investigated for their anti-nociceptive, anti-inflammatory and anti- ulcer properties. A combination of these pharmacol- ogical properties in a single substance is unique since most of the available anti-inflammatory analgesics are ulcerogenics. With the report of Ramaswamy et al. on the anti-nociceptive effect on hydroxyethyl rutoside' , further studies with gossypin 2.4 , epicatechin, flavone s were carried out. It ha s been observed that these fla- vonoid substances produced significant opioid and ATP sensitive (K+ ATP) channel mediated anti-nociceptive response like morphine. However , they exhibited a ceiling effect of 60-70% of the activity. A detailed structure activity relationship using mono-substituted flavone derivatives s indicated only a marginal differ- ence in the anti-nociceptive efficacy of different fla- vone substances. In the present study, attempts have been made to explore more efficacious group of tlavonoid sub- stances by synthesizing di-hydroxyflavones (DHFs) and investigate them for their anti-nociceptive activity and its mechanism. Male Swiss albino mice weighing between 2S-30 g, purchased from King Institute, Ch e nn a i, were housed under normal 12 hr: J 2 hI' li ght dark cycle at Llom temperature (28°-30°C) with fr ee access to food (pel- lets obtained from Gold Moh :: r Lt d .. Banga lore) and water. The experiments we re co nducted between 10.00 and 12.00 hrs. ** Corres pondent author: E- mail: vi su5 3@ hotmail.com The protocol was approved by Institute Ethical Committee, Madras Medical College, Chennai. Measurement of anti-nociception-The acetic acid induced abdominal constriction assal was used. The number of abdominal constrictions for a period of IS min following ip injection of 0.6 % acetic acid (10 mllkg) was counted. A significant reduction in num- ber of constrictions when compared with vehicle treated animals was considered as anti-nociceptive response . Each animal was used only once for the study. Prior to this testing, the effect of DHFs on the motor activity was tested using rota rod. Drug treatment-The newly synthesized six DHFs were suspended in 1% carboxymethyl cellulose (CMC) and were administered 60 min prior to acetic acid challenge in varying doses of 2S-400 mg/kg, s.c. Vehicle treated animals served as control. Role of opioid system-The role of opioid system was studied by administering naloxone (S mg/kg ip) 4S min after DHF administration. Role of K+ ATP channels-This was studied by administering glibenclamide 00 mg/kg , ip) as known K+ ATP sensitive blocker (dose related based on earlier studies) 7.8 . 40 min after DHFs treatment and anti- nociception was measured . D rllg s and chemicals used-The following six DHFs were synthesized at Herborganics , Chcnnal following the standard procedure . Their physico- chemical authentication was also carried out.