What is the most likely cause of the cardiovascular deterioration following administration of propranolol?

A 41-year-old man presented to his general practitioner with symptoms of palpitations, sweating and anxiety. His blood pressure was 160/102 mmHg. He was advised to take propranolol 40 mg twice daily but was admitted to hospital later that week with an episode of pulmonary oedema.

On examination at the time of admission, he was noted to be pale and sweating and he had a blood pressure of 210/124 mmHg. A phaeochromocytoma was suspected.

What is the most likely cause of the cardiovascular deterioration following administration of propranolol?
A . ?1-adrenoceptor blockade leading to acute left ventricular dysfunction
B . inadequate ?-adrenoceptor blockade because of the short half-life of the drug
C . inhibition of catechol-O-methyltransferase by propranolol leading to an increase in circulating noradrenaline
D . loss of ?2-adrenoceptor-mediated vasodilatation
E . propranolol acting as an agonist at ?1-adrenoceptors

Answer: D