Final answer:
Phentolamine is a non-selective alpha-blocker that antagonizes both alpha-1 and alpha-2 adrenergic receptors, it does not bind covalently to the receptors, and typically causes tachycardia, not bradycardia, leading to increased cardiac output.
Step-by-step explanation:
The question pertains to Phentolamine, which is a sympatholytic drug. Phentolamine is not a selective alpha-1 antagonist; rather, it is a non-selective alpha-blocker, meaning it antagonizes both α1 and α2 adrenergic receptors, preventing the normal sympathetic effects that epinephrine and norepinephrine would have, such as vasoconstriction. Therefore, it often leads to vasodilation and a drop in blood pressure.
It does not bind covalently to the alpha receptor; it is a reversible antagonist. Because of the blockage of α-adrenergic receptors, there can be a reflex increase in heart rate (tachycardia), rather than bradycardia, in response to vasodilation and lowered blood pressure. Phentolamine can lead to increased cardiac output due to decreased peripheral resistance.