Effects of clonidine infusion and withdrawal on blood pressure and behaviour in the rat. A preliminary study.

Clonidine (10 micrograms/kg/hr) was administered continuously to normotensive rats for 5 days using osmotic minipumps. This treatment attenuated the episodic fluctuations in blood pressure normally observed during rapid eye movement (REM) sleep. However, 18-24 hr after withdrawal of clonidine, pronounced fluctuations in blood pressure superimposed upon tonic increases in pressure as well as muscular twitching and irregular respiration were seen during sleep. These responses were abolished by an injection of clonidine or phentolamine. The results demonstrate that after withdrawal of clonidine administration, an increased lability of blood pressure occurs during sleep and probably results from an increased frequency and duration of REM sleep.