Priapism is the persistence of erection in the absence of sexual stimulation. The complete pathophysiology is unclear. Primarily, priapism was associated with venous occlusion (low-flow priapism), such as occurs, for example, in sickle cell disease, as a consequence of the injection of vasoactive drugs, which are associated with neoplastic diseases and haemotological malignancies, but also with traumata. Another form is high-flow priapism, in which arterial overflow is considered to be the pathogen. Priapism may also originate from neurological diseases by disturbance of the neuroregulatory mechanisms responsible for erection. On a molecular level, an altered balance of the interaction between NO-induced relaxation and adrenergic stimulation contraction of smooth muscle is of relevance. This concerns also other local factors which influence the erectile tissue, such as endogenous vasoactive substances (e.g. oxygen supply, endothelial factors), neurotransmitters (e.g. NO, vasoactive intestinal peptide VIP), and metabolic events (e.g. androgenic milieu, abnormal expression of ion channels of the smooth muscle cell, abnormal enzyme activities; Burnett 2003).

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