Autonomic Nervous Systems
A patient presents with severe hypertension. The underlying cause-a pheochromocytoma-is not looked for, nor detected in the work-up. An oral antihyp-ertensive drug is prescribed. We soon find that the patient’s BP has gone up to levels above pretreatment levels. Which of the following drugs was most likely administered?
a. Pheochromocytomas—rare causes of hypertension— involve excessive levels of circulating catecholamines from tumors of the adrenal medulla; other chromaffin cells may be affected, leading to excessive catecholamine production in and release from other sites.
b. The main factor in leading to an increase of blood pressure in this condition is a-mediated vasoconstriction arising from excessive levels of epinephrine, norepinephrifle, or both. And, the contributions of epinephrine will involve some β2 vasodilation.
c. That vasodilator effect, no matter how slight, will be blocked by propranolol or any other β adrenergic blocker that can block β receptors. (So-called cardioselective β blockers such as atenolol and metoprolol can also block β2 receptors in the vasculature, and elsewhere, with blood levels that -are not too far above the usual “therapeutic” range.) In essence, blockade of β2 receptors in the vasculature will leave α mediated constrictor effects unopposed, and blood pressure will rise (concomitant with suppression of cardiac contractility and rate).