The Journal of pharmacology and experimental therapeutics
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J. Pharmacol. Exp. Ther. · Apr 1996
Effects of naloxone and D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 and the protein kinase inhibitors H7 and H8 on acute morphine dependence and antinociceptive tolerance in mice.
Previous studies measuring opioid inhibition of cyclic adenosine monophosphate in SH-SY5Y cells supported the hypothesis that continuous agonist stimulation causes a gradual conversion of the mu opioid receptor to a sensitized or constitutively active state termed mu*. Conversion to mu* was prevented by the kinase inhibitor H7, but not its close analog H8. Naloxone was proposed to act as a negative antagonist (inverse agonist) blocking mu* activity, whereas D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) appeared to act as a neutral antagonist having no effect on mu* activity. ⋯ Morphine pretreatment (100 mg/kg, s.c., -5 hr) produced antinociceptive tolerance as shown by a 2.7-fold increase in the calculated morphine A50 value. Tolerance was reversed by H7, but not H8, treatment (50 nmol, i.c.v., -30 min). These results are consistent with the hypothesis that a sensitized or constitutively active mu* state plays a role in narcotic tolerance and dependence.
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J. Pharmacol. Exp. Ther. · Feb 1996
Buprenorphine's physical dependence potential: antagonist-precipitated withdrawal in humans.
Buprenorphine is a partial mu opioid agonist with demonstrated efficacy in the treatment of opioid dependence. One potential advantage of buprenorphine over full mu opioid agonists is its reported low physical dependence profile. This study systematically examined physical dependence produced by maintenance with a clinically relevant dose of buprenorphine using antagonist challenge procedures. ⋯ Significant precipitated withdrawal occurred at 3.0 and 10 mg/70 kg i.m. of naloxone and 3.0 mg/70 kg p.o. of naltrexone. These results indicate that buprenorphine maintenance produces physical dependence and that i.m. naloxone and p.o. naltrexone produce equivalent effects in withdrawal precipitation under these conditions. Findings have implications for selection of antagonist doses for use in formulating combination agonist/antagonist medications and for use in transition of drug abusers from buprenorphine to antagonist maintenance therapies.
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J. Pharmacol. Exp. Ther. · Feb 1996
Differential genetic mediation of sensitivity to morphine in genetic models of opiate antinociception: influence of nociceptive assay.
Several genetic mouse models of opiate sensitivity have been identified or produced in an attempt to investigate mechanisms underlying individual variation in responses to opiate drugs like morphine. The major models in use presently are the DBA/2 (DBA) versus C57BL/6 (C57) inbred strains, the recombinantly inbred CXBK strain, and mouse lines selectively bred for high- and low-magnitude antinociception after swim stress (HA and LA lines, respectively) or levorphanol administration (HAR and LAR lines, respectively). The hot-plate test, an assay of acute, thermal nociception, was used in the selection of the HA/LA and HAR/LAR lines, and has largely been used to characterize the differential opiate sensitivity of the DBA (high) and C57 (low) strains and the deficient sensitivity of the CXBK strain. ⋯ Results indicate a high degree of dissociation between different genetic models, which suggests that these strains differ in their nociceptive and antinociceptive sensitivities due to the effects of very different genetic and physiological mechanisms. In addition, the present findings suggest that morphine inhibits different modalities of nociception via separate mechanisms that can be genetically dissociated and independently altered. Strikingly, in HA/LA and HAR/LAR mice, we find that an inverse relationship exists with respect to morphine antinociceptive sensitivity in the hot-plate and acetic acid abdominal constriction tests, respectively.
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J. Pharmacol. Exp. Ther. · Jan 1996
Comparative StudyBinding of bupivacaine to human serum proteins, isolated albumin and isolated alpha-1-acid glycoprotein. Differences between the two enantiomers are partly due to cooperativity.
Binding parameters of R(+)- and S(-)-bupivacaine were determined for human serum proteins, human alpha-1-acid glycoprotein (AAG) and human serum albumin (HSA), using ultrafiltration. Binding parameters were estimated according to the Scatchard model of the law of mass action using nonlinear regression. A sigmoid (cooperativity) term was added when needed. ⋯ S(-) and R(+) enantiomers exhibited different behavior toward purified AAG and HSA due in part to complex allosteric cooperativity (positive or negative depending on the ligand/protein ratio). In conclusion, we observed stereoselective binding of bupivacaine to AAG and HSA. Moreover, cooperativity occurred, and the behavior of the two enantiomers showed marked differences in this respect.
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J. Pharmacol. Exp. Ther. · Oct 1995
Zatebradine, a specific bradycardic agent, alters the hemodynamic and left ventricular mechanical actions of levosimendan, a new myofilament calcium sensitizer, in conscious dogs.
The cardiovascular and left ventricular (LV) functional effects of levosimendan were examined (LSM; 0.5, 1.0, 2.0 and 4.0 micrograms.kg-1.min-1) in conscious, chronically instrumented dogs (n = 8) in the presence and absence of heart rate control with zatebradine (ZAT) or ZAT alone (0.25, 0.5 and 1.0 mg.kg-1). LSM increased heart rate (HR) cardiac output (CO), diastolic coronary blood flow velocity (DCBFV) and pressure-work index (PWI; calculated myocardial oxygen consumption) and decreased mean arterial, LV systolic and end-diastolic pressures, systemic vascular resistance and diastolic coronary vascular resistance (DCVR). ZAT alone decreased HR and PWI and increased stroke volume. ⋯ LSM increased the maximal rate of segment lengthening to a similar degree in ZAT-treated versus -untreated dogs. ZAT alone had minimal effects on LV function. Control of LSM-induced tachycardia with ZAT decreases myocardial oxygen consumption but also partially attenuates the positive inotropic and lusitropic effects of LSM.