u-50488 and normorphine

The mu antagonist property of the kappa agonist U50,488H was studied at the spinal level, using motility of the rat urinary bladder as an endpoint in vivo. Intrathecal (i.th.) administration of the mu agonists [D-Ala2,NMePhe4,Gly-ol]enkephalin (DAGO), [N-MePhe3,D-Pro4]enkephalin (PL017), morphine and normorphine, as well as the delta agonist [D-Pen2,D-Pen5]enkephalin (DPDPE), resulted in an equieffective inhibition of volume-initiated contractions of the urinary bladder. In contrast, i.th. administration of U50,488H, a highly selective kappa agonist, had no effect on bladder motility. Pretreatment of rats with i.th. U50,488H prior to agonist administration, blocked the suppression of spontaneous bladder activity induced by equieffective i.th. does of morphine and normorphine, but failed to alter the inhibitory effect of the mu agonists DAGO and PL017, or that of the delta agonist DPDPE. The finding that U50,488H differentially antagonized the identical bladder effects of several mu agonists suggests the presence of mu receptor subtypes (mu isoreceptors) in the rat spinal cord, which may be involved in the regulation of bladder function.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Endorphins; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Morphine; Morphine Derivatives; Muscle Contraction; Pyrrolidines; Rats; Receptors, Opioid; Receptors, Opioid, kappa; Receptors, Opioid, mu; Urinary Bladder

In the mouse isolated vas deferens the amplitude of excitatory junction potentials (e.j.p.s) recorded intracellularly from smooth muscle cells varied with the strength of stimulation. Receptor type selective opioids were tested in this preparation. The mu-agonist normorphine (2,000 nmol/l) reduced the amplitude of e.j.p.s and shifted the stimulus-response curve in a parallel way to the right. By contrast, the kappa-agonist U-50488 (1,000 nmol/l) and the delta-agonist [D-Ala2,D-Leu5]-enkephalin (2 nmol/l) caused a non-parallel shift of the curve. In addition, opioids having a lower selectivity for one type of receptor were also used. The preferential kappa-agonists ethylketocyclazocine (40 nmol/l) and dynorphin A1-13 (100 nmol/l) produced parallel and non-parallel shifts, respectively. Thus, normorphine and ethylketocyclazocine were more effective in depressing e.j.p.s evoked by low intensities of stimulation than those evoked by high intensities of stimulation. U-50488, dynorphin A1-13 and [D-Ala2,D-Leu5]-enkephalin caused an equal depression of e.j.p.s evoked by either intensity of stimulation. The preferential mu- and delta-antagonists naloxone (1,000 nmol/l) and ICI 154129 (10,000 nmol/l), reversed the action of the respective agonists normorphine and [D-Ala2, D-Leu5]-enkephalin. In addition, ICI 154129 (10,000 nmol/l) reversed the action of dynorphin A1-13, as well. The preferential kappa-antagonist MR-2266 (1,000 nmol/l) prevented the effect of both ethylketocyclazocine and U-50488. It is concluded that under the conditions of these experiments normorphine and ethylketocyclazocine acted at mu-, U-50488 at kappa-, and dynorphin A1-13 and [D-Ala2,D-Leu5]-enkephalin at delta-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Cyclazocine; Dynorphins; Electric Stimulation; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Ethylketocyclazocine; In Vitro Techniques; Male; Mice; Morphine Derivatives; Muscle, Smooth; Neuromuscular Junction; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Synaptic Transmission

The irreversible non-selective opioid antagonist beta-chlornaltrexamine (beta-CNA) was used in combination with selective mu receptor protection by [D-Ala2, MePhe4, Gly(ol)5]enkephalin (DAGO) to produce an effective kappa receptor antagonism in the guinea-pig field-stimulated ileum preparation. Using a standard pre-treatment of 10(-7) M beta-CNA incubated for 15 min, DAG (10(-6)-10(-4) M) protected the response to the mu agonist normorphine while reducing the antagonism of the kappa agonist U50488 to a lesser extent. The concentration of DAGO which produced the most selective protection was 10(-5) M. This method was used to find the kappa selectivity of a series of opioid agonists. Of the compounds tested, butorphanol, dynorphin-(1-17), U50488, tifluadom, bremazocine and Mr 2034 were the most kappa-selective. The correlation with kappa agonist selectivity in vitro and effects in vitro on urine output in the rat is demonstrated.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Diuresis; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Guinea Pigs; Ileum; In Vitro Techniques; Male; Morphine Derivatives; Naltrexone; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, kappa

Extraluminal strain gage transducers were sutured along the transverse axis of the duodenum in order to monitor circular muscle contractile activity in the pentobarbital anesthetized dog. Administration by intravenous bolus of a variety of mu- and delta-directed opioid ligands resulted in a dose-dependent increase in duodenal contractile activity. In contrast, all kappa-directed ligands were devoid of stimulatory activity. Naloxone reversed the effects of normorphine and [Met5]enkephalin but was 20 times more effective against normorphine than [Met5]enkephalin. Based on the inactivity of all kappa ligands examined and the differential potency of naloxone against [Met5]enkephalin and normorphine, we suggest that this model may be useful in the classification of opioid ligands as to their receptor selectivity in vivo. Further, these data indicate that the stimulation of duodenal contractile activity is not mediated by enteric kappa receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics; Animals; Dogs; Duodenum; Dynorphins; Electric Stimulation; Enkephalin, Methionine; Female; Gastrointestinal Motility; Male; Morphine; Morphine Derivatives; Naloxone; Peptide Fragments; Phenazocine; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu