Myocardial metabolic and functional responses to acetylcholine are altered in thyroxine-induced cardiac hypertrophy

H. R. Weiss, J. Tse

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14 Scopus citations


We tested the hypothesis that acetylcholine would reduce myocardial 02 consumption and function, and that thyroxine (T4, 0.5 mg/kg for 16 days) induced cardiac hypertrophy would change this relationship. Anesthetized open-chest New Zealand white rabbits were divided into four groups: control-vehicle (CV, n = 8), control-acetylcholine (CA, n = 10), T4-vehicle (T4V, n = 9), and T4-acetylcholine (T4A, n = 10). Either vehicle or acetylcholine (10-3 M) was topically applied to the left ventricular surface. Coronary blood flow (radioactive microspheres) and 02 extraction (microspectrophotometry) were used to determine 02 consumption, and muscarinic receptor density and affinity were also determined. T4 increased the heart weight/body weight ratio from 2.6 ± 0.1 to 3.4 ± 0.1. T4-treated animals had higher heart rates, blood pressures, and left ventricular dP/dt(max) than control rabbits. Topical acetylcholine depressed hemodynamic parameters with a greater decrement in pressures and cardiac output in the T4A group (CA, -25%, T4A, -40%). Myocardial O2 consumption and coronary brood flow were higher in the T4-treated hearts. Myocardial O2 consumption significantly declined in both groups during acetylcholine, but the reduction was greater in the T4-treated hearts (CV 7.9 ± 0.4 to CA 5.8 ± 0.6 and T4V 18.8 ± 3.0 to T4A 7.3 ± 1.0 mL 02·min-1·100 g-1). Muscarinic receptor density (B(max)) was elevated by 41% in the T4-treated hearts, but affinity (K(d)) was not altered. Thus, the T4-treated hearts responded to acetylcholine to a greater extent than control hearts in terms of functional and 02 consumption decrements. This may, in part, be related to the elevated number of muscarinic receptors in the T4-treated rabbit hearts.

Original languageEnglish (US)
Pages (from-to)729-735
Number of pages7
JournalCanadian Journal of Physiology and Pharmacology
Issue number6
StatePublished - Jan 1 1995

All Science Journal Classification (ASJC) codes

  • Physiology
  • Pharmacology
  • Physiology (medical)


  • Acetylcholine
  • Cardiac hypertrophy
  • Coronary blood flow
  • Muscarinic receptors
  • Myocardial O consumption
  • Rabbit
  • Thyroxine

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