![]() While local application of a muscarinic antagonist (scopolamine) that blocks the pupil sphincter completely abolishes the pupillary effects of morphine in the rabbit, application of a sympathetic neuronal blocker (guanethidine) or of an alpha- adrenergic antagonist (phentolamine) that block the pupil dilator had no effect in those experiments. In contrast, dogs show normal responses following sympathectomy. For example, Lee and Wang have shown that dogs with a sectioned oculomotor nerve fail to show miosis even with a 30 fold increase in the dose of morphine. It is generally accepted, however, that sympathetic innervation is not essential, the miotic effect being entirely dependent on the integrity of the parasympathetic system. The exact site, or sites, of action within the CNS, which are responsible for opioid-induced miosis remain obscure. Others have suggested that miosis is caused by stimulation of opioid receptors located on the iris sphincter, although this opinion seems to be in the minority. An alternative view has been postulated that morphine depresses cortical centers, which normally inhibit the Edinger-Westphal nucleus. That morphine produces its effects by direct stimulation of the Edinger-Westphal (preganglionic parasympathetic) nucleus. The increase in truncal rigidity was instantly reversed by a low dose (25 mg/70 kg body weight) of the fast acting muscle relaxant succinylcholine. In comparison to the rapid bolus injection of the drug, slow injection over a period of 2min resulted in a significant lesser reduction of thoracic compliance. Alfentanil-induced truncal rigidity in patients following induction of anesthesia. Theories have been advanced suggestingįigure II-59. ![]() This action is a specific opioid effect as demonstrated by its antagonism by naloxone. Opioid-induced miosis in the human, dog and rabbit is thought to be mediated through the central nervous system. Yet, the mechanisms behind this and related effects of opioids on the eye in humans and laboratory animals have just begun to be explored. The neural pathways responsible for regulating pupil size are reasonably well defined. The miotic action of opioids on the pupil is an easily recognizable and quantifiable effect in man.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |