Articles: analgesics.
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1 The antinociceptive effects of systemically-administered procaine, lignocaine and bupivacaine were examined in mice and rats by using the hot-plate, writhing and tail flick tests. 2 In both species all three local anaesthetics produced significant antinociception which was prevented by atropine (5 mg kg-1, i.p.) and by hemicholinium-3 (1 microgram per mouse, i.c.v.), but not by naloxone (3 mg kg-1, i.p.), alpha-methyl-p-tyrosine (100 mg kg-1, s.c.), reserpine (2 mg kg-1, i.p.) or atropine methylbromide (5.5 mg kg-1, i.p.). 3 Atropine (5 mg kg-1, i.p.) which totally antagonized oxotremorine (40 micrograms kg-1, s.c.) antinociception did not modify morphine (5 mg kg-1, s.c.) or baclofen (4 mg kg-1, s.c.) antinociception. On the other hand, hemicholinium, which antagonized local anaesthetic antinociception, did not prevent oxotremorine, morphine or baclofen antinociception. 4 Intracerebroventricular injection in mice of procaine (200 micrograms), lignocaine (150 microgram) and bupivacaine (25 micrograms), doses which were largely ineffective by parenteral routes, induced an antinociception whose intensity equalled that obtainable subcutaneously. Moreover, the i.c.v. injection of antinociceptive doses did not impair performance on the rota-rod test. 5 Concentrations below 10(-10) M of procaine, lignocaine and bupivacaine did not evoke any response on the isolated longitudinal muscle strip of guinea-pig ileum, or modify acetylcholine (ACh)-induced contractions. On the other hand, they always increased electrically-evoked twitches. 6 The same concentrations of local anaesthetics which induced antinociception did not inhibit acetylcholinesterase (AChE) in vitro. 7 On the basis of the above findings and the existing literature, a facilitation of cholinergic transmission by the local anaesthetics is postulated; this could be due to blockade of presynaptic muscarinic receptors.
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In opiate-naive rats, the endogenous opioid peptides, beta-endorphin, dynorphin(1-13) and Met-Enk-Arg-Phe (MEAP) and the synthetic enkephalin analogue D-Ala2-D-Leu5-Enk (DADLE) potently stimulated plasma corticosterone in a dose-dependent, naloxone reversible manner. To characterize their in vivo affinities, the effects of these peptides on plasma corticosterone release were tested in rats made tolerant to morphine, U50488H, DADLE/morphine or beta-endorphin. These cross-tolerance studies showed that dynorphin and MEAP exerted their action on plasma corticosterone release at kappa-opioid receptors. ⋯ These results indicate that there is independent modulation of the hypothalamic-pituitary-adrenal axis by endogenous opioid peptides at mu-, delta- and kappa-opioid receptors. In addition there may be modulation by beta-endorphin at a separate site that we suggest could be a central epsilon-receptor site. This cross-tolerance paradigm, using a neuroendocrine model, provides in vivo evidence for the action of centrally active endogenous opioid peptides at multiple and independent opioid receptors.
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Randomized Controlled Trial Comparative Study Clinical Trial
Epidural sufentanil versus intramuscular buprenorphine for postoperative analgesia. A double-blind comparative trial.
Epidural sufentanil 50 micrograms was compared with intramuscular buprenorphine 0.3 mg for postoperative pain relief. Patients were assigned randomly to one of two treatment groups and received both an intramuscular and epidural injection, one of which was a placebo. ⋯ Cardiovascular variables remained stable in all patients and no respiratory depression was observed. Side effects were more frequent following buprenorphine.