title: Central alpha 2-adrenoceptor-mediated pressor response to clonidine in conscious, spontaneously hypertensive rats.
abstract: Pressor responses to intracerebroventricular (i.c.v.) injection of clonidine were investigated in conscious spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Clonidine (1-10 micrograms, i.c.v.) caused a dose-dependent pressor response and decrease in heart rate in both SHR and WKY. In SHR, low doses (1, 2.5 micrograms) but not high doses (5, 10 micrograms) of i.c.v.-clonidine induced a depressor response following the pressor response. Both pressor and depressor responses to i.c.v.-clonidine were significantly greater in SHR than in WKY. In both SHR and WKY, pressor responses to i.c.v.-clonidine were abolished by pentobarbital anesthesia, pretreatment with i.v.-furosemide (5 mg/kg), 24-hr water deprivation and pretreatment with i.c.v.-yohimbine (100 micrograms), but not by pretreatment with i.v.-yohimbine (100 micrograms) and i.c.v.-prazosin (10 micrograms). On the 1st day after surgery for arterial catheter implantation, SHR reduced their water intake, and i.c.v.-clonidine (5 micrograms) caused a slight pressor response, whereas the same dose of clonidine on the 7th day after surgery resulted in a marked pressor response. These results suggest that clonidine caused a central alpha 2-adrenoceptor-mediated pressor response, which is greater in SHR than in WKY and is sensitive to body fluid volume changes and anesthesia.
authors.affiliation: Department of Pharmacology, Miyazaki Medical College, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kawasaki
authors.forename: S
authors.initials: S
authors.lastname: Nakamura
authors.forename: K
authors.initials: K
authors.lastname: Takasaki
mesh_terms: D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D003000:Clonidine / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005665:Furosemide / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects*; D006973:Hypertension / Q000503:physiopathology*; D007276:Injections, Intraventricular; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D014868:Water Deprivation; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D005665:Furosemide; D003000:Clonidine; D011224:Prazosin