Introduction
ICl 154,129 is a new compound that shows selectivity as an antagonist of [Leu5]enkephalin and [D-AIa2, D-Leu5]enkephalin at opiate receptors in the mouse vas deferens preparation. The recent finding shows that ICI 154,129 is active in rats in a novel model of delta receptor activation.
Pharmacologic action
ICI 154,129 shows selectivity as an antagonist of [Leu5]enkephalin and [D-AIa2, D-Leu5]enkephalin at opiate receptors. At s.c. doses of 30 and 100 mg/kg, ICl 154,129 had no marked effect on the gastrointestinal transit of a charcoal meal in rat. And in the rat, ICI 154,129 microinjection was given at 1300h, and the amount of corpus luteinizing hormone (LH) formation increased in the early stage. Then the amplitude was larger, the peak time was earlier than 1h, and the peak amplitude was about 100% larger than the control group. ICI 154,129 reverses the effect of leu-enkephalin (delta agonist) more effectively than normorphine (mu agonist), whereas naloxone is the opposite of a range of other antagonists. When ICI 154,129 tested a series of opioid agonists, it was shown to be more effective against leu-enkephalin and [D-AIa2, D-Leu5]enkephalin, thought to act at delta sites, than against the mu receptor agonist normorphine and the kappa agonist ethylketocyclazocine. The pharmacological effects of ICI 154,129 require further investigation, but it may be necessary to synthesize compounds with greater selectivity and potency before reaching conclusions about their selective antagonistic properties in vivo.
Function
A positive impact of ICI 154129 is an increase in recorded feeds in the food intake test. ICI 154,129 prevents the bradycardia produced by opioid agonists, but its actions are not selective for the agonist subtype and requires doses of 40 μmol/kg. ICI 154,129 produced an advance in and augmentation of the surge of LH secretion when administered in-traventricularly just before the critical period for the surge of LH secretion. The effects of ICI 154,129 on the LH secretion in proestrus seemed somewhat different from those of naloxone.
References:
Shaw, J.S., Miller, L., Turnbull, M.J., Gormley, J.J. and Morley, J.S., Selective antagonists at the opiate delta-receptor, Life Sci., 31 (1982) 1259-1262.
Holaday, J.W., Ruvio, B.A., Robles, L.E., Johnson, C.E. and D'Amato, R.J., M154,129: A putative delta antagonist reverses endotoxic shock without altering morphine analgesia, Life Sci., 31 (1982) 2209-2212.
Litchfield, J.T. and Wilcoxon, F., A simplified method of evaluating dose-effect experiments, J. Pharmacol. Exp. Ther., 96 (1949) 99-I13.
