a group of scientists wanted to study erection in a rat model and we will suppose it works exactly like human.
they knew that parasympathetic innervation caused erection by relaxing the helicine resistance vessels but they wanted to know the exact mechanism.
first off they gave atropine and sexually excited the subject and it resulted in a normal erection.
the 2nd experience was to give atropine and damage the endothelium and give atropine it resulted in erection again after stimulation.
in shock but not out of idea they decided to give methylarginine first alone and then with atropine and damaged endothelium
it resulted both in no/very weak erection.
what your deduction about the erectile mechanism from this experience?