naltrindole and 17-cyclopropylmethyl-6-7-didehydro-4-5-epoxy-5--guanidinyl-3-14-dihydroxyindolo(2--3--6-7)morphinan

To learn the involvement of endogenous opioid peptides (EOP) in the regulation of reproductive activity in ruminants, the effects of different opioid antagonists on luteinizing hormone (LH) secretion were determined in sheep during the early stage of lactation. The opioid receptor antagonists: naloxone (all types of receptors, n=5), naloxonazine (μ receptor, n=5), GNTI- (κ receptor, n=5), naltrindole (δ receptor, n=5) or the vehicle (control, n=5) were infused intracerebroventricularly in a series of five 30-min infusions (60μg/60μl) at 30-min intervals. The period of the experiment included the non-suckling (10:00-12.30) and suckling (12.30-15.00) periods. Blood samples were collected from 10.00 to 15.00 at 10-min intervals, and plasma LH concentration was assayed by the radioimmunoassay method. The obtained results showed that blocking of the EOP action within the central nervous system in lactating sheep caused a significant (p<0.001) increase in LH concentration in all treated groups, in comparison to the control. In the naloxone-treated group, a significant (p<0.05) increase in LH secretion also occurred during suckling. The amplitude of LH pulses increased significantly in the naloxonazine- (p<0.01) and naltrindole- (p<0.05) treated ewes compared to the control; there were no significant differences in the frequency of LH pulses among the groups. In conclusion, our study indicates that EOP play a crucial role in the mechanism inhibiting GnRH/LH axis activity in lactating sheep and that the ligands for μ opioid receptor may have the highest inhibitory effect.

Topics: Animals; Female; Gene Expression Regulation; Guanidines; Lactation; Luteinizing Hormone; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Receptors, Opioid; Sheep

Recently, it has been known that the antinociception of sildenafil, a phosphodiesterase 5 inhibitor, is mediated through the opioid receptors. There are common three types of opioid receptors mu, delta, and kappa. We characterized the role of subtypes of opioid receptor for the antinociception of sildenafil at the spinal level. Intrathecal catheters were placed for drug delivery and formalin solution (5%, 50 microl) was injected for induction of nociception within male SD rats. The effect of mu opioid receptor antagonist (CTOP), delta opioid receptor antagonist (naltrindole), and kappa opioid receptor antagonist (GNTI) on the activity of sildenafil was examined. Intrathecal sildenafil decreased the flinching responses during phases 1 and 2 in the formalin test. Intrathecal CTOP and naltrindole reversed the antinociception of sildenafil during both phases in the formalin test. Intrathecal GNTI reversed the effect of sildenafil during phase 2, but not phase 1. These results suggest that sildenafil is effective to acute pain and the facilitated pain state at the spinal level. Both mu and delta opioid receptors are involved. However, it seems that kappa opioid receptors play in the effect of sildenafil.

Topics: Animals; Behavior, Animal; Dose-Response Relationship, Drug; Drug Administration Routes; Drug Interactions; Guanidines; Male; Morphinans; Naltrexone; Narcotic Antagonists; Pain Measurement; Pain Threshold; Phosphodiesterase Inhibitors; Piperazines; Purines; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Sildenafil Citrate; Somatostatin; Sulfones; Time Factors

To examine the receptor specificity and the mechanism of opioid peptide-induced protection, we examined freshly isolated adult rabbit cardiomyocytes subjected to simulated ischemia. Cell death as a function of time was assessed by trypan blue permeability. Dynorphin B (DynB) and Met5-enkephalin (ME) limitation of cell death (expressed as area under the curve) was sensitive to blockade by naltrindole (NTI, a delta-selective antagonist) and 5'-guanidinyl-17-(cyclopropylmethyl)-6,7-dehydro-4,5alpha-epoxy-3,14-dihydroxy-6,7-2',3'-indolomorphinan (GNTI dihydrochloride, a kappa-selective antagonist): 85.7 +/- 2.7 and 142.9 +/- 2.7 with DynB and DynB + NTI, respectively (P < 0.001), 94.1 +/- 4.2 and 164.5 +/- 7.3 with DynB and DynB + GNTI, respectively (P < 0.001), 111.9 +/- 7.0 and 192.1 +/- 6.4 with ME and ME + NTI, respectively (P < 0.001), and 120.2 +/- 4.3 and 170.0 +/- 3.3 with ME and ME + GNTI, respectively (P < 0.001). Blockade of ATP-sensitive K+ channels eliminated DynB- and ME-induced protection: 189.6 +/- 5.4 and 139.0 +/- 5.4 for control and ME, respectively (P < 0.001), and 210 +/- 5.9 and 195 +/- 6.1 for 5-HD and ME + 5-HD, respectively (P < 0.001); 136.0 +/- 5.7 and 63.4 +/- 5.4 for control and ME, respectively (P < 0.001), and 144.6 +/- 4.5 and 114.6 +/- 7.7 for HMR-1098 and ME + HMR-1098, respectively (P < 0.01); 189.6 +/- 5.4 and 139.0 +/- 5.4 for control and ME, respectively (P < 0.001), and 210 +/- 5.9 and 195 +/- 6.1 for 5-HD and ME + 5-HD, respectively (P < 0.001); and 136.0 +/- 5.7 and 63.4 +/- 5.4 for control and ME, respectively (P < 0.001), and 144.6 +/- 4.5 and 114.6 +/- 7.7 for HMR-1098 and ME + HMR-1098, respectively (P < 0.01). We conclude that opioid peptide-induced cardioprotection is mediated by delta- and kappa-receptors and involves sarcolemmal and mitochondrial ATP-sensitive K+ channels.

Topics: Adenosine Triphosphate; Animals; Benzamides; Cardiotonic Agents; Dose-Response Relationship, Drug; Dynorphins; Endorphins; Enkephalin, Methionine; Guanidines; Ischemic Preconditioning, Myocardial; Male; Mitochondria; Morphinans; Myocardial Ischemia; Myocytes, Cardiac; Naltrexone; Narcotic Antagonists; Potassium Channels; Rabbits; Receptors, Opioid, delta; Receptors, Opioid, kappa; Sarcolemma

The indole moiety in the delta-opioid antagonist, naltrindole (2, NTI), was employed as a scaffold to hold an "address" for interaction with the kappa-opioid receptor. The attachment of the address to the 5'-position of the indole moiety was based on superposition of NTI upon the kappa antagonist, norbinaltorphimine (1, norBNI). A variety of cationic groups were employed as a kappa address in an effort to investigate its interaction with the anionic address subsite, Glu297, on the kappa receptor. Some of the groups that were employed for this purpose were amines, amidines, guanidines, and quaternary ammonium. Members of the series were found to have a varying degree of kappa antagonist potency and kappa selectivity when tested in smooth muscle preparations. The 5'-guanidine derivative 12a (GNTI) was the most potent member of the series and had the highest kappa selectivity ratio. GNTI was 2 times more potent and 6-10-fold more selective than norBNI (1). In general, the order of potency in the series was: guanidines > amidines approximately quaternary ammonium > amines. The kappa antagonist potency appeared to be a function of a combination of the pK(a) and distance constraint of the cationic substituent of the ligand. Receptor binding studies were qualitatively in agreement with the pharmacological data. Molecular modeling studies on 12a suggested that the protonated N-17 and guanidinium groups of GNTI are associated with Asp138 (TM3) and Glu297 (TM6), respectively, while the phenolic hydroxyl may be involved in donor-acceptor interactions with the imidazole ring of His291. It was concluded that the basis for the high kappa selectivity of GNTI is related both to association with the nonconserved Glu297 residue and to unfavorable interactions with an equivalent position in mu- and delta-opioid receptors.

Topics: Cell Line; Guanidines; Humans; Indoles; Models, Molecular; Morphinans; Morphine Derivatives; Naltrexone; Narcotic Antagonists; Receptors, Opioid, kappa; Structure-Activity Relationship; Transfection

Topics: Amino Acid Sequence; Animals; Binding, Competitive; COS Cells; Guanidines; Guinea Pigs; Ileum; In Vitro Techniques; Male; Mice; Models, Molecular; Molecular Conformation; Molecular Sequence Data; Morphinans; Muscle, Smooth; Mutation; Naltrexone; Narcotic Antagonists; Rats; Receptors, Opioid, kappa; Receptors, Opioid, mu; Vas Deferens