• The primary indication for an inoconstrictor is a situation where inotropic support is required in the face of low systemic vascular resistance. Inodilators are suited to situations where low cardiac output is associated with high systemic vascular resistance.
• Catecholamines have an agonist effect at the bradrenergic receptor in cardiac muscle, increasing cytoplasmic cAMP which is the fulcrum of all inotropic activity.
• Phosphodiesterase inhibitors exert their inotropic action by inhibiting the breakdown of cAMP by its specific enzyme phosphodiesterase III.
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