Final answer:
Yohimbine is the alpha-2 receptor antagonist that was used for treating sexual dysfunction by blocking α2-receptors and increasing sympathetic nervous system activity.
Step-by-step explanation:
The alpha-2 receptor antagonist previously used in the treatment of sexual dysfunction is yohimbine. Alpha-2 receptors are one of the receptor subclasses that epinephrine and norepinephrine bind to, coming in subtypes such as α2A, α2B, and α2C. Antagonists, in general, are substances that bind to receptors and produce an effect that is opposite to that of the endogenous ligand. Yohimbine, extracted from the bark of the Yohimbe tree, has traditionally been used because it blocks α2-receptors, which are thought to help facilitate sexual function by increasing sympathetic nervous system activity.