SulfonesPurinesPiperazinesNitrogenPhosphodiesterase InhibitorsPhosphodiesterase 5 Inhibitors3',5'-Cyclic-GMP PhosphodiesterasesErectile DysfunctionDietary ProteinsCyclic Nucleotide Phosphodiesterases, Type 5UreaAmino AcidsPenile ErectionHomosexuality, MaleMethamphetamineVasodilator AgentsAnimal FeedCyclic GMPGeorgiaUnsafe SexRisk-TakingSexual BehaviorEnteric Nervous System