Complex sentence: At first, the vasoconstrictive effect of alpha-receptors dominates, but with continued use of an alpha agonist, this effect fades first, allowing the vasodilation due to beta-receptor stimulation to emerge.
Split into simpler sentences: At first, the vasoconstrictive effect of alpha-receptors dominates. This effect fades first, allowing the vasodilation due to beta-receptor stimulation to emerge.