Schematic representation of the molecular pathophysiologic mechanisms of RIP that has a likely local vasculogenic association. Normal penile erection physiology depicted on top. This schema does not preclude other neurogenic or hormonal factors that may be involved in eliciting priapism. Decreased basal levels of PDE5 enzyme permits uncontrolled erection (priapism) because of the lack of the normal regulatory control mechanism involved in the return of the penis back to its flaccid state. Circular arrows signify the pathway between penile erection states. Horizontal black arrows signify regulation. Horizontal black T-shapes signify inhibition. Downward black arrows signify downregulation.