Effect of Phenylephrine on the Accommodative System

Figure 3

Agonist versus antagonist behaviour. The substances naturally produced by our body act on cellular receptors. The agonist is not the natural substance, but it acts similarly occupying the receptors and activating them, imitating or even enhancing therefore the effect produced by the natural substance. On the contrary, an antagonist mimics the natural substance to take its place in the receptor, blocking thus the cellular activity.

(a)

(b)