GTN sprays are currently in trials for use in ED. This means they don't yet know the safety, efficacy, etc., of using it on the penis.
Do you know the cause of your ED? You should talk to a doctor if you don't. Many times, there is a simple physical problem that can be treated, and it can sometimes indicate a serious health problem that needs to be addressed.
Please talk to your doctor before using ANYTHING to treat your ED.