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This study is an attempt to study the influence of clonidine, which has a central sympatholytic action, on the renal function in dogs and to elucidate its mechanism of action. Clonidine (15mcg/kg) injected into a cephalic vein of the dog produced a marked increase in urine flow and in amounts of Na+ and K+ excreted in urine, and clearances of free water and osmolar substance, the reabsorption rates of Na+ and K+ in renal tubules were significantly decreased. Clonidine (50.0mcg/kg) administered intravenouly elicited a transient reduction in urine flow, along with inhibition of all renal functions. Intravenous clonidine-induced diuretic effect was completely blocked by pretreatment with reserpine, and was lessened by water diuresis. Clonidine (3.Omcg/kg) injected into a carotid artery revealed a transient diuresis with a increase in clearance of free water. Clonidine injected into a renal artery showed a significant antidiuretic effect and all functions of an experimental kidney were reduced. Antidiuretic action induced by clonidine given into a renal artery markedly suppressed by pretreatment with reserpine. The above results suggest that clonidine has dual mechanisms: 1) diuretic effect due to the central sympatholytic action and inhibition of release of antidiuretic hormone, and 2) antidiuretic effect indued by indirect symptheic stimulation in the periphery.
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