title: Clonidine reverses the slowly developing hypertension produced by low doses of angiotensin II.
abstract: We used the centrally acting sympatholytic drug clonidine to evaluate neurogenic pressor activity in rats made hypertensive by chronic intravenous infusion of a low dose (4.0 ng.min-1) of angiotensin II (Ang II). Male Sprague-Dawley rats were instrumented with arterial and venous catheters and then housed in metabolic cages for the duration of the experiment. After 3 days of recovery from surgery, daily measurements were begun of mean arterial pressure, heart rate, water balance, and urinary electrolyte excretion. After 3 days of control measurements rats received either Ang II (4.0 ng.min-1 IV, n = 5) or saline vehicle (n = 4) continuously over a 15-day period. After the Ang II and vehicle infusions were ended, measurements were made during 3 days of recovery. On days 2, 7, and 12 of the experimental infusion period, clonidine hydrochloride was administered as a bolus (10.0 micrograms.kg-1 IA). The resulting changes in mean arterial pressure and heart rate were assessed over a 6-hour period. Fluid measurements were evaluated on a daily basis. In rats receiving only vehicle, clonidine produced no significant changes in any variable at any time. In rats given Ang II, mean arterial pressure increased from a control value (mean +/- SEM) of 106 +/- 1 mm Hg to 135 +/- 6, 139 +/- 6, and 148 +/- 4 mm Hg on days 2, 7, and 12, respectively. The antihypertensive response to clonidine after 6 hours on days 2, 7, and 12 of the Ang II infusion in these rats was -18 +/- 8, -16 +/- 5, and -23 +/- 9 mm Hg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology and Toxicology, Michigan State University, East Lansing 48823.
authors.forename: V J
authors.initials: VJ
authors.lastname: Gorbea-Oppliger
authors.forename: G D
authors.initials: GD
authors.lastname: Fink
mesh_terms: D000804:Angiotensin II / Q000008:administration & dosage; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology*; D006973:Hypertension / Q000139:chemically induced* / Q000188:drug therapy / Q000503:physiopathology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000804:Angiotensin II; D003000:Clonidine