Drugs that act as inotropic sympathomimetics

Question 1

Inotropic effect of sympathetic stimulation

Answer 1

As end diastolic pressure increases, the stroke work during subsequent systole increases. When sympathetic nerve stimulation is applied, this markedly accentuates the Starling effect so that with increasing frequency of nerve stimulation, there is an increase in stroke work.

Question 2

Effects on receptors of sympathetic nerve stimulation

Answer 2

Noradrenaline is released from the stimulated nerve and acts on B1 and B2 receptors on ventricular myocytes. Stimulation of the B receptors stimulates a signal transduction cascade that results in increased intracellular Ca concentration.

Question 3

Inotropic sympathomimetic drugs

Answer 3

Synthetic agonists of B1 and B2 receptors in the cardiac myocytes can be used to strengthen the force of contraction. These drugs effectively mimic the effects of noradrenaline so they are called inotropic sympathomimetics. Dobutamine, dopamine and isoprenaline have predominant B1 selectivity, while dopexamine has B2 selectivity. They are only used in intensive settings or emergency medicine e.g. haemorrhade, sepsis.