Neuropeptide Y (NPY) in human penile corpus cavernosum tissue and circumflex veins--occurrence and in vitro effects

The concentration and distribution of neuropeptide Y (NPY) within the penile corpus cavernosum (CC) and in penile circumflex veins (CV) from healthy potent males was investigated by immunochemistry and immunohistochemistry. The concentrations were assessed to 28.6 pmol/gm. (CC) and 15.8 pmol/gm. (CV) respectively. Gel filtration on CC tissue extracts demonstrated a single peak of NPY-immunoreactivity (NPY-IR) similar to synthetic human NPY. The NPY-IR was confined to nerve fibers seemingly innervating smooth muscle cells. In vitro myographic examinations demonstrated contractile activation by NPY in 2/8 CC strips and in 5/8 CV strips. The mean contractile force was 1.17 +/- 0.62 mN (18.3 +/- 15.8% of the K(+)-induced contraction) and 2.42 +/- 0.42 mN (31 +/- 12%) respectively. NPY 10(-7) and 10(-6) M displayed a potentiating effect on the response to NA 10(-9) in one of six CC and four of six CV preparations. It is suggested that NPY could add to the contractile effect of NA in detumescence and in maintenance of the resting state; contribution of NPY to the veno-occlusive mechanism at initiation of erection is another putative physiological function.