morphinans and naloxonazine

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

Suckling by newborns induces a surge of lactogenic hormones, that is prolactin and growth hormone (GH), in mother's body, with endogenous opioid peptide (EOP) participating in generation of this surge. The aim of the current study was to investigate which types of opioid receptors are involved in generation of the GH surge in ewes during suckling. A series of intracerebroventricular infusions of opioid receptors antagonists: naloxone (for all types of receptors), naloxonazine (specific for μ receptor) and 5'-guanidinonaltrindole (GNTI--specific for κ receptor) and the vehicle (control) were performed in nursing sheep during the fifth week of lactation. All infusions were carried out in a serial manner: five 30-min infusions (60 μg/60 μl) from 10:00 to 15:00, at 30-min intervals. The period of the experiment consisted of the non-suckling (10:00-12:30) and suckling (12:30-15:00) periods. Simultaneously, blood samples were collected at 10-min intervals to determine plasma GH concentration by radioimmunoassay. Suckling evoked a rapid increase in GH concentration in control ewes. Naloxone and naloxonazine significantly decreased both the basal GH release in the non-suckling period and the suckling-induced GH surge. Specifically, the suppressive effect concerned either the duration or the amplitude of the GH surge. In contrast, GNTI did not significantly affect the GH release. In conclusion, the EOPs may affect the regulatory process of GH secretion in lactating sheep, especially through μ opioid receptor.

Topics: Animals; Female; Growth Hormone; Guanidines; Infusions, Intraventricular; Lactation; Morphinans; Naloxone; Receptors, Opioid, kappa; Receptors, Opioid, mu; Sheep

To investigate the role of opioid μ-receptor subtype in opiate-induced constipation (OIC).. The effect of loperamide on intestinal transit was investigated in mice. Ileum strips were isolated from 12-wk-old male BALB/c mice for identification of isometric tension. The ileum strips were precontracted with 1 μmol/L acetylcholine (ACh). Then, decrease in muscle tone (relaxation) was characterized after cumulative administration of 0.1-10 μmol/L loperamide into the organ bath, for a concentration-dependent study. Specific blockers or antagonists were used for pretreatment to compare the changes in loperamide-induced relaxation.. In addition to the delay in intestinal transit, loperamide produced a marked relaxation in isolated ileum precontracted with ACh, in a dose-dependent manner. This relaxation was abolished by cyprodime, a selective opioid μ-receptor antagonist, but not modified by naloxonazine at a dose sufficient to block opioid μ-1 receptors. Also, treatment with opioid μ-1 receptor agonist failed to modify the muscle tone. Moreover, the relaxation by loperamide was attenuated by glibenclamide at a dose sufficient to block ATP-sensitive K+ (K(ATP)) channels, and by protein kinase A (PKA) inhibitor, but was enhanced by an inhibitor of phosphodiesterase for cyclic adenosine monophosphate (cAMP).. Loperamide induces intestinal relaxation by activation of opioid μ-2 receptors via the cAMP-PKA pathway to open K(ATP) channels, relates to OIC.

Topics: Acetylcholine; Analgesics, Opioid; Animals; Antidiarrheals; Constipation; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Gastrointestinal Transit; Glyburide; Humans; Intestine, Small; Loperamide; Male; Mice; Mice, Inbred BALB C; Morphinans; Muscle Relaxation; Naloxone; Receptors, Opioid, mu

The role of opioid receptors in the regulation of vascular function remains unclear. In the current study, we evaluated the ability of loperamide, a peripheral opioid receptor agonist, to regulate blood pressure in spontaneously hypertensive rats (SHRs) and examined the mechanism(s) by which loperamide exerts its effects.. In male SHRs, mean arterial pressure (MAP) was measured and hemodynamic analysis was recorded. Additionally, the isometric tension of aortic rings isolated from SHRs was determined.. Loperamide dose-dependently decreased MAP in SHRs but not in the normal group of Wistar-Kyoto rats. This reduction of MAP in conscious SHRs was abolished by the selective opioid μ-receptor antagonist cyprodime, but not by naloxonazine, the μ(1)-opioid receptor antagonist. However, cardiac output was not altered by loperamide in anesthetized SHRs. Moreover, loperamide-induced relaxation in isolated aortic rings precontracted with phenylephrine or vasopressin. This relaxation was abolished by cyprodime, but not by naloxonazine. Loperamide-induced relaxation was also attenuated by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker. Additionally, vasodilatation by loperamide was reduced by an inhibitor of protein kinase A (PKA) and enhanced by an inhibitor of phosphodiesterases.. We suggest that loperamide can lower MAP in SHRs via μ(2)-opioid receptor-dependent cAMP-PKA pathway that induces vascular relaxation by opening K(ATP) channels.

Topics: Animals; Arteries; Blood Pressure; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Endothelium; Glyburide; Hemodynamics; Intracellular Signaling Peptides and Proteins; KATP Channels; Loperamide; Male; Morphinans; Naloxone; Phenylephrine; Phosphodiesterase Inhibitors; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Opioid, mu; Vasodilation

Intravenous (i.v.) administration of morphine produces a dose-dependent inhibition of the tail-flick (TF) reflex, depressor response, and bradycardia in the rat. Some of these effects depend on interactions of i.v. morphine with peripheral opioid receptors and the integrity of cervical vagal afferents. The present studies used the relatively specific mu, delta, and kappa opioid receptor agonists (DAGO, DPDPE or U-50,488H) and the relatively specific mu, delta, and kappa opioid receptor antagonists (beta-FNA, naloxonazine, naltrindole or nor-BNI) in either intact rats or rats with bilateral cervical vagotomy (CVAG) to delineate the vagal afferent/opioid-mediated components of these effects. I.v. administration of DAGO in intact rats produced a dose-dependent inhibition of the TF reflex, depressor response, and bradycardia virtually identical to those produced by i.v. morphine. All of these effects of either i.v. DAGO or i.v. morphine were significantly attenuated by either bilateral CVAG or pre-treatment with the mu 2 opioid receptor antagonist beta-FNA. Pre-treatment with the mu 1 opioid receptor antagonist naloxonazine affected i.v. DAGO-induced inhibition of the TF reflex and bradycardia, but had no significant effects on i.v. morphine-produced responses. I.v. administration of DPDPE produced a dose-dependent pressor response, but had no marked effects on the either the TF reflex or heart rate (HR). The pressor response was unaffected by either bilateral CVAG or pre-treatment with naltrindole, naloxone, hexamethonium, or bertylium. i.v. administration of U-50,488H produced a depressor response and bradycardia, but had no significant effect on the TF reflex. The depressor response and bradycardia produced by i.v. U-50,488H were unaffected by bilateral CVAG, but could be antagonized by pre-treatment with either nor-BNI or naloxone. These studies suggest that the vagal afferent-mediated antinociceptive and cardiovascular effects of i.v. morphine are primarily mediated by interactions with low affinity mu 2 opioid receptors.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analysis of Variance; Animals; Blood Pressure; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Heart Rate; Hexamethonium; Hexamethonium Compounds; Indoles; Injections, Intravenous; Male; Morphinans; Morphine; Naloxone; Naltrexone; Narcotic Antagonists; Narcotics; Pain; Pyrrolidines; Rats; Rats, Sprague-Dawley; Reference Values; Time Factors; Vagotomy; Vagus Nerve

[D-Ala2]deltorphin I effects on fetal respiratory activity was characterized to determine the role delta-opioid receptors play in modulating fetal respiratory activity. [D-Ala2]deltorphin I, infused at 0.3 or 100 micrograms/h, intracerebroventricularly (i.c.v.), stimulated fetal respiratory activity without changing blood pH, PCO2 or PO2. Stimulation by 0.3 micrograms/h, but not 100 micrograms/h, was blocked by i.c.v. infusion of the delta-opioid receptor antagonist, naltrindole. Stimulation by 100 micrograms/h was blocked by the mu 1-opioid receptor antagonist naloxonazine. These data suggest stimulation of fetal respiratory activity by 0.3 micrograms/h [D-Ala2]deltorphin I are mediated specifically through delta-opioid receptors; while [D-Ala2]deltorphin I at 100 micrograms/h is no longer selective for the delta-opioid receptor, and the stimulation may be mediated through the mu 1-opioid receptor.

Topics: Animals; Dose-Response Relationship, Drug; Electromyography; Female; Fetus; Indoles; Injections, Intraventricular; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Oligopeptides; Pregnancy; Receptors, Opioid, delta; Respiration; Sheep

Tail-pinch feeding (TPF) in rats is decreased following general (naltrexone, NTX) and mu (Cys2-Tyr3-Orn5-Pen7-amide, CTOP) opioid antagonists, but not following kappa (nor-binaltorphamine. Nor-BNI) or delta (naltrindole, NTI) opioid antagonists. Because multiple mu (mu1 and mu2) and delta (delta 1 and delta 2) opioid receptor subtypes have been characterized, the present study evaluated whether TPF was differentially altered following ICV administration of general (NTX), mu (beta-funaltrexamine, B-FNA), mu1 (naloxonazine, NAZ), kappa (Nor-BNI), delta 1 ([D-Ala2, Leu5, Cys6]-enkephalin, DALCE) and delta 2 (NTI) opioid antagonists. Like the reversible mu antagonist CTOP, the irreversible mu antagonist B-FNA significantly and dose-dependently (1-20 micrograms) reduced TPF by up to 28%. In contrast, whereas NAZ (50 micrograms) reduced TPF by 32%, this effect was highly variable and failed to achieve significance. Neither NTX (5-10 mg/kg, SC), Nor-BNI (20 micrograms), DALCE (40 micrograms) nor NTI (20 micrograms) significantly altered TPF, suggesting that kappa, delta 1 and delta 2 opioid receptor subtypes were not involved. Because no antagonist altered the duration of food contact during tail pinch, it appears that the opioid effect modulates ingestive rather than activational mechanisms. The reliable inhibition of TPF by B-FNA (mu1 and mu2), together with the variable effect of naloxonazine (mu1), appears to implicate both mu binding sites in this response.

Topics: Animals; Arousal; Enkephalin, Leucine-2-Alanine; Feeding Behavior; Indoles; Male; Morphinans; Naloxone; Naltrexone; Narcotic Antagonists; Nociceptors; Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu

To determine whether opioid receptors or the more recently characterized naloxone-sensitive substance P (SP) N-terminal binding sites play a role in desensitization to the behavioral effects of SP, we assessed the effects of selective antagonists at mu-(naloxonazine and beta-funaltrexamine), delta- (naltrindole) and kappa- (nor-binaltorphimine) opioid receptors, as well as the effect of [D-Pro2,D-Leu7]SP-(1-7) D-SP-(1-7) (D-SP (1-7)), an inhibitor of [3H]SP-(1-7) binding, on behaviors induced by intrathecally administered SP in mice. Whereas naloxone, a non-selective opioid antagonist, inhibited the development of behavioral desensitization to SP, the response to repeated SP administration remained unaffected by pretreatment with selective opioid antagonists. Like naloxone, however, the SP-(1-7) antagonist inhibited SP-induced desensitization. The protection against desensitization to SP by D-SP-(1-7), but not by selective antagonists of mu, delta or kappa receptors, suggests that desensitization to the behavioral effects of SP does not appear to be mediated by an action at an opioid receptor but by an action at the SP-(1-7) binding site.

Topics: Analysis of Variance; Animals; Behavior, Animal; Binding Sites; Indoles; Injections, Spinal; Male; Mice; Morphinans; Naloxone; Naltrexone; Peptide Fragments; Substance P

Mr2034 has been proposed as a kappa opiate. While Mr2034 inhibited the binding of the kappa opiate 3H-ethylketocyclazocine better than unlabeled ethylketocyclazocine, it also displaced the binding of 3H-dihydromorphine and 3H-SKF 10047 more potently than morphine and SKF 10047, respectively. 3H-D-ala2-D-leu5-enkephalin was displaced equally well by Mr2034 and D-ala2-D-leu5-enkephalin. Saturation studies of 3H-Mr2034 binding demonstrated curvilinear Scatchard plots which could be dissected into two components by computer: KD1 0.06 nM, Bmax1 2.49 fmoles/mg tissue; and KD2 2.4 nM, Bmax2 6.57 fmoles/mg tissue. A portion of the higher affinity (KD 0.06 nM) component was inhibited by naloxonazine treatment in vitro (50 nM), suggesting that 3H-Mr2034 bound with very high affinity to mu1 sites. Displacement of 3H-Mr2034 binding by opioids was multiphasic, again implying that 3H-Mr2034 was binding to more than one class, of site. In view of its similar potency in inhibiting mu (3H-dihydromorphine), kappa (3H-ethylketocycla-zocine), sigma (3H-SKF 10047) and delta (3H-D-ala2-D-leu5-enkephalin) opioids Mr2034 might be considered a universal opiate.

Topics: Animals; Benzomorphans; Brain; Cyclazocine; Dihydromorphine; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Ethylketocyclazocine; Male; Morphinans; Naloxone; Phenazocine; Rats; Rats, Inbred Strains; Receptors, Opioid