title: Effects of ricin on the ability of rabbit arteries to contract and relax.
abstract: Ricin, a toxic lectin from castor beans, reduces blood pressure. The current studies determined the effect of ricin on contractions in response to norepinephrine (NE) of rabbit central ear artery, endothelium-dependent relaxations to methacholine and ATP of aorta rings and endothelium-independent relaxations to papaverine in central ear artery and aorta rings. Rabbits were given 0.11 or 0.22 micrograms kg-1 ricin i.v. and 18 h, 4 days, or 7 days later the arteries were removed and tested. Maximal contractions to NE were increased by 8-23% (P > 0.05) with ricin treatment. The EC50 was increased in five of six ricin-treated groups, although only significantly so at 18 h after a minimum lethal dose of ricin. Maximum relaxations to methacholine were increased by 20-57% (P > 0.05) at 18 h following both ricin doses but returned to control values at later time points. Relaxations in response to ATP were significantly enhanced in all ricin-treated groups (95-205%) except in the 18 h and 4-day 0.11 microgram kg-1 dose groups where the increase was 0-46%. Relaxations in response to papaverine were not altered in either artery. Thus, ricin decreases the sensitivity of the rabbit central ear artery to NE and increases endothelial-dependent relaxations of the rabbit aorta. Therefore, decreased blood pressure following ricin administration may be due to vasodilation caused by decreased vascular contractions and increased endothelial-dependent vascular relaxation.
authors.affiliation: University of Oklahoma Health Sciences Center, College of Pharmacy, Oklahoma City 73190, USA.
authors.forename: V J
authors.initials: VJ
authors.lastname: Christiansen
authors.forename: C H
authors.initials: CH
authors.lastname: Hsu
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.forename: C P
authors.initials: CP
authors.lastname: Robinson
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D004431:Ear, External / Q000098:blood supply; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D007928:Lethal Dose 50; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010208:Papaverine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D012276:Ricin / Q000008:administration & dosage / Q000633:toxicity*; D014439:Tyramine / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects
chemical_list: D011189:Potassium Chloride; D012276:Ricin; D010208:Papaverine; D009638:Norepinephrine; D014439:Tyramine