Renal effects of medetomidine in isoflurane-anesthetized dogs with special reference to its diuretic action

Renal effects of the selective alpha2-adrenoceptor agonist, medetomidine, were investigated in anesthetized dogs. Animals were administered medetomidine 20 and 40 micro g/kg intravenously (IV) and 80 micro g/kg intramuscularly (IM) or 1 ml of saline IV. Urine and blood samples were collected before and at 30. 60, 90 and 120 min following medetomidine injection. Mean arterial blood pressure (MABP), renal blood flow (RBF), glomerular filtration rate (GFR), urine volume (Uv), urine osmolality (Uosm), free water clearance (CH2O). fractional clearance of sodium (FNa), plasma osmolality (Posm), plasma glucose levels and plasma antidiuretic hormone (ADH) concentrations were measured. The results showed that IV administration of medetomidine initially increased MABP 5-15 rain followed by long-lasting decrease. The initial hypertension was not observed after IM administration, which was accompanied by a more profound hypotensive effects. RBF, GFR, Uv, CH2O increased after IV injection and decreased after IM. Medetomidine increased FNa and Posm and decreased Uosm. Plasma glucose levels initially increased and subsequently decreased. Plasma ADH concentration was decreased by IV injection but increased by IM administration. Our data imply that: 1) IV administration of medetomidine at dose rates of 20 and 40 micro g/kg results in profound diuresis up to 2 hr; 2) Suppression of ADH release from me CNS is one of the mechanisms of medetomidine-induced diuresis although it may not be the principal one.