Effects of some peptides on isolated human penile erectile tissue and cavernous artery

Contractant and relaxant effects of four peptides known to occur in nerves innervating human penile vessels and erectile tissue, namely substance P (SP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and somatostatin, were studied in isolated preparations from the corpus cavernosum (CC), corpus spongiosum (CS) and cavernous artery (Acc). In addition, the actions of another peptide, arginine vasopressin (AVP), were investigated. In erectile tissue proper, SP induced concentration-dependent contractions. No effect of this peptide was observed in Acc segments. CC and CS preparations contracted by noradrenaline (NA) were relaxed by 30-40%; the effect in NA-contracted Acc preparations was inconsistent. AVP had a potent contractant effect in preparations from all the tissues studied, the effect being most conspicuous in CS strips. VIP was without contractant actions in any of the preparations. NA-contracted preparations were relaxed by VIP, and electrically induced contractions inhibited. The inhibitory effect was particularly marked in electrically stimulated CC and CS preparations. NPY had no effects; somatostatin contracted Acc segments, and in high concentrations CC and CS strips. It is concluded that among the peptides studied only VIP has effects compatible with a role as a neurotransmitter in penile erection.