Evidence that the novel imidazoline compound FT005 is an alpha(2)-adrenoceptor agonist

1: The aim of this study was to determine whether the hyperglycaemic action of the novel imidazoline compound FT005 could be mediated by activation of alpha(2)-adrenoceptors, using a variety of in vivo and in vitro methods including radioligand binding. 2: FT005 produced a dose-dependent increase in blood glucose levels of CBA/Ca mice (0.125-25 mg kg(-1), i.p.). The time course of this hyperglycaemic effect matched that of adrenaline (1 mg kg(-1)) more closely than glucagon (1 mg kg(-1)) or the K(ATP) channel opener diazoxide (25 mg kg(-1)). The hyperglycaemic effect of FT005 (1 mg kg(-1)) was significantly reduced by the alpha(2)-adrenoceptor antagonist rauwolscine (0.5 mg kg(-1)). 3: FT005 produced a significant reduction in plasma insulin levels of mice 30 min after administration. The hyperglycaemic effect of FT005 (25 mg kg(-1)), although still present, was significantly less in fasted mice in which insulin levels are lower, suggesting that a reduction of insulin secretion contributes to the action of FT005. 4: When studied in the mouse isolated vas deferens preparation, FT005 produced a complete inhibition of neurogenic contractions, which was blocked by rauwolscine. This is consistent with activation of pre-synaptic alpha(2)-adrenoceptors. 5: In radioligand binding studies FT005 completely displaced the alpha(2)-adrenoceptor antagonist [(3)H]-RX821002 from mouse whole brain homogenates. The displacement was best described by a two-site model of interaction comprising high and low affinity components. 6: The results indicate that FT005 is an agonist at alpha(2)-adrenoceptors. A reduction in insulin secretion contributes to the hyperglycaemic action of FT005, although an additional mechanism can not be excluded.