Effects of Abrupt Cessation of Treatment with Clonidine and Guanfacine on Blood Pressure and Heart Rate in Spontaneously Hypertensive Rats

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Abstract
The effects of clonidine and guanfacine withdrawal were compared on blood pressure in spontaneously hypertensive rats. Five week oral administration of clonidine at a dose of .apprx. 300 .mu.g/kg per day produced a significant hypotension. After acute interruption of clonidine administration a marked blood pressure rise was observed. Peak blood pressure rise was reached within 24 h after clonidine withdrawal. A significant increase in plasma norepinephrine concentration was observed when clonidine treatment was discontinued. Long-term administration of guanfacine at a dose of .apprx. 3 mg/kg per day produced a significant hypotension. After a 5 wk administration of guanfacine, abrupt cessation did not produce a rapid blood pressure rise. Catecholamine concentration in urine and plasma was not influenced by guanfacine administration or its withdrawal.