title: Attenuation of reflex pressor and ventilatory responses to static muscular contraction by intrathecal opioids.
abstract: We have tested the hypothesis that intrathecal injections of opioid peptides attenuate the reflex pressor and ventilatory responses to static contraction of the triceps surae muscles of chloralose-anesthetized cats. We found that before intrathecal injections of [D-Ala2]Met-enkephalinamide (100 micrograms in 0.2 ml), static contraction increased mean arterial pressure and ventilation by 32 +/- 5 (SE) mmHg and 227 +/- 61 (SE) ml/min, whereas after injection of this opioid peptide, static contraction increased mean arterial pressure and ventilation by only 15 +/- 5 mmHg and 37 +/- 33 ml/min, respectively. The attenuation of both the pressor and ventilatory responses to static contraction by [D-Ala2]Met-enkephalinamide were statistically significant (P less than 0.05). Moreover, the attenuation was probably not caused by an opioid-induced withdrawal of sympathetic outflow because [D-Ala2]Met-enkephalinamide had no effect on the pressor and ventilatory responses evoked by high-intensity electrical stimulation of the central cut end of the sciatic nerve. In addition, intrathecal injection of peptides that were highly selective agonists for either the opioid mu- or delta-receptor attenuated the reflex responses to static contraction. Naloxone (1,000 micrograms), injected intrathecally, prevented the attenuation of the reflex responses to contraction by opioid peptides. We speculate that the opioid-induced attenuation of the reflex pressor and ventilatory responses to static contraction may have been due to suppression of substance P release from group III and IV muscle afferents.
authors.affiliation: Department of Internal Medicine, University of California, Davis 95616.
authors.forename: J M
authors.initials: JM
authors.lastname: Hill
authors.forename: M P
authors.initials: MP
authors.lastname: Kaufman
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004744:Enkephalin, Methionine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D007278:Injections, Spinal; D009119:Muscle Contraction / Q000502:physiology*; D012119:Respiration / Q000187:drug effects* / Q000502:physiology; D012584:Sciatic Nerve / Q000502:physiology
chemical_list: D004745:Enkephalins; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D020881:Enkephalin, D-Penicillamine (2,5)-