Question

Describe the mechanism of action of intravenous injection of epinephrine or norepinephrine. What effect is expected on heart rate and blood pressure? How it affects blood vessels and circulation?

Answer 1

Epinephrine and norepinephrine are adrenergic drugs.

Mechanisms:-

- They act directly as agonist on alpha and beta adrenoceptors.

- alpha and beta are adrenergic receptors present on different organic.

- Epinephrine act on heart by beta1 receptor present on the heart.

- Epinephrine increase the heart rate by increasing the slope of diastolic depolarization of cells in the SA node. It also activates latent pacemaker in A-V node and Purkinje fibres.

- force of cardiac contraction is increased. Cardiac output and oxygen consumption of the heart are markedly enhanced.

- thereby it increases the blood pressure. It causes rise in systolic and diastolic and mean blood pressure.

- Epinephrine primarily causes vasoconstriction which is mediated by alpha receptor on blood vessels.

- It causes dilatation in the blood vessels in muscles, liver, and coronaries. This effect is mediated by beta receptors.

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