title: Effects of brimonidine ingestion on cardiovascular responses and renal function in conscious dogs.
abstract: The effects of brimonidine, an alpha(2)-adrenoceptor agonist, on blood pressure, heart rate, respiratory rate, renal function and some blood parameters were investigated in 10 dogs. Dogs were divided into two groups, low dose (LD; 0.2 mg/kg) and high dose (HD; 0.5 mg/kg) of brimonidine given orally. The alpha(2)-adrenergic antagonist yohimbine hydrochloride was injected to dogs at a dose of 0.1 mg/kg in both groups at the fifth hour after brimonidine administration. The results demonstrated that after administration of brimonidine, mean arterial blood pressure decreased dramatically at 2 h by 23% and 20% in LD and HD groups, respectively. Heart rate was decreased in a similar manner and both remained low at 5 h after brimonidine administration. Respiratory rate was decreased by 50%, while the electrocardiogram showed prolongation of the PR interval. Glomerular filtration rate (GFR) and effective renal blood flow were reduced when measured at 4 h after brimonidine ingestion in both groups, but the effect was more pronounced in the LD group. Brimonidine caused natriuresis and kaliuresis in both LD and HD groups. The packed cell volume was decreased and hyperglycaemia was detected. Most of the effects can be reversed completely after administration of yohimbine. However, yohimbine can restore GFR only partially. These data suggest that brimonidine caused cardiovascular and respiratory depression. The adverse effects of this drug can be antagonized by yohimbine, suggesting that these effects were mediated via the alpha(2)-adrenoceptor.
authors.affiliation: Department of Physiology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand.
authors.forename: S
authors.initials: S
authors.lastname: Suwanwipat
authors.forename: C
authors.initials: C
authors.lastname: Buranakarl
authors.forename: N
authors.initials: N
authors.lastname: Chaiyabutr
mesh_terms: D000284:Administration, Oral; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D000068438:Brimonidine Tartrate; D002319:Cardiovascular System / Q000187:drug effects*; D004285:Dogs / Q000502:physiology*; D004347:Drug Interactions; D004562:Electrocardiography / Q000187:drug effects / Q000662:veterinary; D004573:Electrolytes / Q000652:urine; D005260:Female; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D007668:Kidney / Q000187:drug effects*; D008297:Male; D011810:Quinoxalines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D017596:Renal Plasma Flow, Effective / Q000187:drug effects; D012119:Respiration / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology; D010130:p-Aminohippuric Acid / Q000652:urine
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004573:Electrolytes; D011810:Quinoxalines; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D010130:p-Aminohippuric Acid