title: Alpha 2-adrenoceptor blocking properties of the alpha 1-selective agonist 2-(2-chloro-5-trifluoromethylphenylimino)imidazolidine (St 587).
abstract: The selective alpha 1-adrenoceptor agonist 2-(2-chloro-5-trifluoromethylphenylimino)imidazolidine (St 587) was tested with respect to putative alpha 2-adrenoceptor blocking properties. In these studies 6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepine (B-HT 920) was used as a selective alpha 2-adrenoceptor agonist. At peripheral presynaptic sites St 587 (1 mg/kg i.v.) significantly antagonized the inhibitory effect of B-HT 920 (3-30 micrograms/kg i.v.) on electrically induced tachycardia in pithed rats. To study influences on central sympathoinhibition, urethane anaesthetized, vagotomized rats were used. Parameter measured was heart rate and this was decreased by B-HT 920. St 587 antagonized this effect in the range 1-10 mg/kg s.c. in a dose-dependent manner. These vagotomized rats were pretreated with prazosin, thus a central stimulation of alpha 1-adrenoceptors by St 587 was excluded. In anaesthetized dogs with beta-adrenoceptors blocked 10 micrograms/kg B-HT 920 intracisternally promoted a vagally mediated reflex bradycardia as elicited by angiotensin. St 587 given 20 min later with 100 micrograms/kg intracisternally almost completely abolished this effect. In mice, the exploratory activity was greatly diminished by treatment with the alpha 2-adrenoceptor agonists B-HT 920 (200 micrograms/kg s.c.) or azepexole (20 mg/kg s.c.) and this effect was partly antagonized by St 587 (0.1 or 1 mg/kg i.p.). In behavioral experiments dogs treated with St 587 (0.3-10 mg/kg i.v.) showed signs of irritation, especially in higher doses. Dogs treated with B-HT 920 (0.3 mg/kg i.v.) fell into a narcotic state, dogs treated in addition with St 587 (0.3-3 mg/kg i.v.) remained conscious but were remarkably sedated.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.forename: L
authors.initials: L
authors.lastname: Pichler
authors.forename: W
authors.initials: W
authors.lastname: Kobinger
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001522:Behavior, Animal / Q000187:drug effects; D003000:Clonidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004285:Dogs; D004347:Drug Interactions; D004558:Electric Stimulation; D005106:Exploratory Behavior / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D051379:Mice; D011224:Prazosin / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects; D051381:Rats; D013116:Spinal Cord / Q000502:physiology; D014628:Vagotomy
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001381:Azepines; C030655:St 587; C024763:talipexole; D003000:Clonidine; D011224:Prazosin