An etorphine-evoked vagal reflex in rats is inhibited by naloxone, N-methylnaloxone, and SMS 201-995.
Intravenous injection of opiates in rats is known to produce a rapid fall in heart rate, blood pressure, and respiratory frequency. Etorphine, a potent opiate agonist which reaches central and peripheral receptors, administered at 1.1 nmol/kg i.v., evoked these characteristic effects in the urethane-anaesthetized rat. Three opiate antagonists, with somewhat different properties, have been used to assess the site of action of etorphine-induced bradycardia, hypotension, and inhibition of respiration. The antagonists used were naloxone hydrochloride, N-methylnaloxone bromide, and SMS 201-995. Low doses of naloxone blocked the cardiovascular and respiratory effects of etorphine. N-Methylnaloxone blocked the bradycardia, hypotension and the initial phase of apnea produced by etorphine but not the subsequent slowing of respiration. SMS 201-995 blocked the bradycardia and partially antagonized the hypotension and inhibition of respiratory rate produced by etorphine. These results indicate that N-methylnaloxone and SMS 201-995 can block the peripheral receptors which mediate opiate-induced bradycardia. Naloxone blocks both the central and peripheral actions of etorphine and so more completely antagonizes the cardiovascular and respiratory effects of etorphine.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D005048:Etorphine / Q000037:antagonists & inhibitors*; D006339:Heart Rate / Q000187:drug effects; D004091:Hydromorphone / Q000031:analogs & derivatives*; D008297:Male; D009019:Morphinans / Q000037:antagonists & inhibitors*; D009270:Naloxone / Q000494:pharmacology*; D015282:Octreotide; D010111:Oxymorphone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects*; D012119:Respiration / Q000187:drug effects; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000494:pharmacology; D014630:Vagus Nerve / Q000502:physiology*
D009019:Morphinans; D009270:Naloxone; D005048:Etorphine; D013004:Somatostatin; D010111:Oxymorphone; D004091:Hydromorphone; D015282:Octreotide