Tachycardia heart failure alters rabbit aortic smooth muscle responsiveness to angiotensin II

E. Porsa, G. L. Freeman, J. T. Herlihy

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7 Scopus citations

Abstract

The effects of heart failure on the responsiveness of aortic smooth muscle tissue to various vasoactive agents were examined. Heart failure was induced in rabbits by sustained rapid ventricular pacing (400 beats/min) for 6-7 wk. After the rabbits were killed, strips of thoracic aorta were prepared and mounted in tissue baths. Responsiveness of these aortic strips to potassium depolarization and cumulative additions of vasoactive agents was determined. Aortic strips from control and tachycardia heart failure (THF) rabbits developed similar maximum forces to stimulation by potassium depolarization (0.77 ± 0.08 vs. 0.96 ± 0.16 kg/cm2), calcium chloride (0.71 ± 0.09 vs. 0.88 ± 0.06 kg/cm2), and phenylephrine (0.90 ± 0.08 vs. 1.14 ± 0.09 kg/cm2). The maximum relaxation to isoproterenol was also unaffected by THF (0.08 ± 0.02 vs. 0.07 ± 0.01 kg/cm2). In contrast, the maximum response of aortic strips from THF rabbits to angiotensin II was significantly lower than control (0.37 ± 0.07 vs. 0.069 ± 0.09 kg/cm2). With regard to aortic smooth muscle sensitivity, no differences in the concentrations at which 50% of the maximal response is achieved (EC50) were observed between THF and control strips for calcium chloride (0.10 ± 0.01 vs. 0.16 ± 0.04 mM), isoproterenol (51.5 ± 13.5 vs. 51.0 ± 5.4 nM), and phenylephrine (65.2 ± 12.3 vs. 92.5 ± 18.0 nM). However, THF was associated with a significant increase in the EC50 value for angiotensin II response (2.03 ± 0.25 vs. 0.58 ± 0.05 nM). These results demonstrate that THF is associated with a specific and significant reduction in the sensitivity and maximal responsiveness of aortic smooth muscle to angiotensin II. THF-induced alterations in the characteristics of angiotensin II receptors may be responsible for these changes.

Original languageEnglish (US)
Pages (from-to)H1228-H1232
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume266
Issue number3 35-3
DOIs
StatePublished - 1994

Keywords

  • calcium
  • isoproterenol phenylephrine
  • potassium depolarization
  • vascular smooth muscle

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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