The adrenergic nervous system in hyperthyroidism: Therapeutic role of beta adrenergic blocking drugs

The adrenergic nervous system plays an important role in hyperthyroidism. The signs id symptoms secondary to adrenergic stimulation include nervousness, anxiety, restlessness, sweating, heat intolerance, tremor, weight loss, palpitations, tachycardia, increases in myocardial contractility, systolic blood pressure, stroke volume, and pulse pressure, decreased peripheral vascular resistance, and ocular stare. In general, the adrenergic effects, particularly those directed at the heart, appear to be mediated by an increase in effective concentrations of catecholamines rather than hypersensitivity to normal levels of catecholamines. Recognition of the adrenergic component in hyperthyroidism has led to various therapeutic interventions in the adjunctive treatment of hyperthyroidism. Initially, the antiadrenergic drugs reserpine and guanethidine were utilized; however, their delayed onset of action, frequency and prolonged duration of side effects have tempered their use. In recent years such beta adrenergic blocking drugs as propranolol have become the drugs of choice for decreasing the adrenergic effects of hyperthyroidism. Propranolol significantly improves the tachycardia, tremor, restlessness, anxiety, sweating, heat intolerance, and myopathy. It has minor effects on the eye signs and does not alter oxygen consumption, goiter, exophthalmos, or the tests of thyroid function. Propranolol is most useful for the short term control of potentially dangerous or disabling symptoms until more definitive therapy renders the patient euthyroid. It is also useful in the treatment of thyroid storm, in patients who are allergic to antithyroid drugs, and in conjunction with radioiodine therapy. It may also be efficacious in the preoperative preparation of patients for surgery. Propranolol is contraindicated in patients with congestive heart failure, chronic lung disease, heart block, patients receiving myocardial depressants, patients receiving psychotropic drugs such as monoamine oxidase inhibitors, patients subject to spontaneous hypoglycemia such as diabetics being treated with insulin or hypoglycemic drugs, and pregnancy.