Effects of pentobarbitone and decerebration on the clonidine-induced circulatory changes.
Clonidine 5 and 15 mug/kg i.v. was given to conscious rats, to rats under pentobarbitone anaesthesia and to decerebrated rats. Clonidine 100 mug/kg was given to conscious and to decerebrated rats. Blood pressure and heart rate were recorded via indwelling catheters. The low dose of clonidine gave virtually no response in the conscious rats but produced hypotension and bradycardia in decerebrated and in anaesthetized rats. After clonidine 15 mug/kg the blood pressure of decerebrated rats decreased further, while conscious and anaesthetized rats showed a hypertensive response. The basal blood pressure and heart rate were significantly higher in the decerebrated rats than in the conscious rats. After the highest dose of clonidine, however, the blood pressure of the decerebrated rats decreased below the basal level of the conscious rats and the blood pressure of the conscious rats increased above the basal level of the decerebrated rats. The results suggest that the hypotensive response is caused by a mechanism located in the medulla oblongata. At higher concentrations clonidine may elicit a hypertensive effect by activating suprabulbar centers. The importance of this suprabulbar effect is attenuated by pentobarbitone anaesthesia.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000008:administration & dosage / Q000494:pharmacology*; D003655:Decerebrate State / Q000503:physiopathology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D008297:Male; D010424:Pentobarbital / Q000494:pharmacology*; D051381:Rats; D013997:Time Factors
D010424:Pentobarbital; D003000:Clonidine