Nitric oxide and the cyclic GMP system in the penis

Since the discovery that nitric oxide is the mediator of penile erection, c onsiderable evidence has been accumulated in experimental animals and men r egarding the pharmacology and molecular biology of the nitric oxide/cGMP pa thway in the penis. This review examines the expression and tissue localiza tion of nitric oxide synthase isoforms (NOS) in this organ and the function al significance of their variants. The disregulation of the balance between nitric oxide synthesis and the com pliance of the corpora cavernosa smooth muscle in relation to erectile dysf unction in animal models is discussed. The possible up-regulation of NOS le vels and the interaction of NOS variants with protein modulators of their a ctivity is analyzed in the context of novel concepts of gene therapy of ere ctile dysfunction.