The glans is a continuation of the corpus spongiosum and is therefore mostly a “spongy” tissue. While there might be some small arterioles, their enlargement wouldn’t make much difference. As we’ve said before, glans growth is rather difficult to attain because it has no tunica. It’s like a balloon which returns to its usual size after expansion. Besides, the surface irritation from something like retin-a probably would not be worth the trouble.