Abstract
The positive inotropic effects of β-agonists (isoprenaline, dobutamine, dopamine), histamine, phosphodiesterase inhibitors (isobutylmethylxanthine, milrinone, theophylline), ouabain and calcium were measured using contracting papillary muscles from healthy guinea-pig hearts as well as on contracting papillary muscle strips from patients undergoing mitral valve replacement. In the guinea-pig myocardium, the potencies varied markedly but all compounds gave the same maximal increase in force of contraction. In contrast, compounds acting through cAMP gave maximal positive inotropic effects which were significantly reduced compared with ouabain and calcium in human papillary muscle strips. Further, the potency of β-agonists was decreased in the diseased human ventricular myocardium.
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