THE EFFECTS OF IDAZOXAN AND OTHER ALPHA-2-ADRENOCEPTOR ANTAGONISTS ON FOOD AND WATER-INTAKE IN THE RAT

1 Idazoxan (1, 3, 10 mg kg-1, i.p.) produced a significant increase in food an 2 The more selective and specific alpha-2-adrenoceptor antagonists, RX811059 (0.3, 1, 3 mg kg-1, i.p.) and RX821002 (0.3, 1, 3 mg kg-1, i.p.), did not produce hyperphagia in rats, however, the highest dose produced a significant increase in water intake. 3 The peripherally acting alpha-2-adrenoceptor antagonist, L-659,066 (1, 3, 10 mg kg-1, i.p.), did not affect food intake in the 4 h following injection, but the highest dose (10 mg kg-1), produced a large increase in water intake. 4 These results indicate that alpha-2-adrenoceptor antagonists may increase water intake by a peripherally mediated mechanism. 5 The lack of effect of RX811059 and RX821002 on food intake contrasts with the large dose-related increases induced by idazoxan and suggests that the hyperphagic effects of idazoxan are not due to alpha-2-adrenoceptor blockade but may instead reflect its affinity for a non-adrenoceptor site, a property not shared by the other alpha-2-antagonists.