Abstract:
The objective of the present study was to investigate the effect of alpha 2- adrenoceptor agonist brimonidine on cardiovascular and renal function, and acid-base balance in dogs. Ten dogs were randomly divided into 2 groups, low-dose (0.2 mg/kg) and high dose (0.5 mg/kg) of brimonidine administration. Blood pressure and heart rate were measured continuously throughout the experimental period. Electrocardiography, rectal temperature, respiratory rate, hematocrit, plasma total solid, blood glucose and blood gas analysis were all performed before and 3 hour hourly after administration of brimonidine and re-measureed again after yohimbine HCl was infused intravenously. Glomerular filtration rate (GFR), effective renal plasma and renal blood flow (ERPF and ERBF), fractional excretion (FE) of the electrolytes, osmolar and free water clearance were determined before and in the 4-5th hour after brimonidine ingestion and recheck again after yohimbine was injected. Mean arterial pressure, heart rate, GFR, ERPF, ERBF, respiratory rate and hematocrit were all reduced significantly, while P-R interval and FE of sodium were increased in response to brimonidine ingestion. In low dose-group of brimonidine, renal functions were more attenuated than high dose-group. There was no apparent effect on acid-base balance. Most parameters completely reversed after alpha 2-antagonist yohimbine administration intravenously. In conclusion, brimonidine plays the role on alpha 2-adrenoceptor to produce the cardiovascular and respiratory depression and reduce ERPF, ERBF and also GFR. The higher dose of brimonidine caused less renal vasoconstriction than lower dose. The effects of brimonidine were mostly reversed by using of alpha 2- antagonist yohimbine hydrochloride.
