title: Long-term treatment with low-dose, but not high-dose, guanethidine improves ventricular function and survival of rats with heart failure after myocardial infarction.
abstract: OBJECTIVE
  We sought to evaluate the effects of various doses of guanethidine, a sympathoinhibitory drug, on ventricular function and survival in chronic heart failure (CHF) after myocardial infarction (MI) in rats.
  
  
  BACKGROUND
  Direct inhibition of sympathetic outflow by a sympathoinhibitory drug might be an effective approach to therapy of CHF. However, recent clinical trials suggest that excessive suppression of sympathetic activity has an adverse effect on outcome. It remains unclear whether the beneficial effects of the sympathoinhibitory drug would be modified by its dosage.
  
  
  METHODS
  Three doses of guanethidine (low-dose [LG], 1 mg/kg/day; medium-dose, 3 mg/kg/day; high-dose, 10 mg/kg/day) were administered via an osmotic mini-pump for 4 weeks. Hemodynamics, left ventricular (LV) diameters, plasma and myocardial norepinephrine (NE) levels, and survival were determined for four weeks after MI.
  
  
  RESULTS
  As compared with MI rats receiving vehicle, LG suppressed LV dilation (9.2 +/- 0.9 mm vs. 11.0 +/- 0.8 mm, p < 0.05) and improved LV fractional shortening (25.0 +/- 4.5% vs. 16.4 +/- 4.7%, p < 0.05) in association with a reduction of plasma NE levels (520 +/- 250 pg/ml vs. 1,000 +/- 570 pg/ml, p < 0.05), but not with a significant reduction of noninfarcted myocardial NE levels (154 +/- 71 ng/g vs. 207 +/- 71 ng/g). Low-dose guanethidine reduced 24-h (6%) and 28-day mortality (6%), as compared with untreated MI rats (36% and 52%, respectively). High-dose guanethidine also reduced 24-h mortality (12%) but increased 28-day mortality (91%), in association with a depletion of myocardial NE. Medium-dose guanethidine had no beneficial effects on LV hemodynamics or long-term survival.
  
  
  CONCLUSIONS
  These results indicate that the dosage of the sympathoinhibitory drug might be quite important for the treatment of CHF.
authors.affiliation: Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Sugitani, Toyama, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Igawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Nozawa
authors.forename: Nozomu
authors.initials: N
authors.lastname: Fujii
authors.forename: Bun-ichi
authors.initials: B
authors.lastname: Kato
authors.forename: Hidetsugu
authors.initials: H
authors.lastname: Asanoi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Inoue
mesh_terms: D000818:Animals; D002395:Catecholamines / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D006145:Guanethidine / Q000008:administration & dosage / Q000494:pharmacology*; D006333:Heart Failure / Q000209:etiology / Q000401:mortality / Q000503:physiopathology*; D008297:Male; D009203:Myocardial Infarction / Q000150:complications*; D051381:Rats; D017208:Rats, Wistar; D013565:Sympatholytics / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D016276:Ventricular Function / Q000187:drug effects*
chemical_list: D002395:Catecholamines; D013565:Sympatholytics; D006145:Guanethidine