Role of Endothelium-derived Relaxing and Hyperpolarizing Factors in the Relaxation of the Corpus Cavernosum

Park, Kwangsung; Kim, Eunyoung; Lee, Jongeun; Ryu, Soobang

Abstract

It has been found that acetylcholine releases at least two different substances from the vascular endothelial cells, i.e., relaxing factor and hyperpolarizing factor. The present study was armed to investigate whether and to what extent these factors are involved in the relaxation of the corpus cavernosum. The corpus cavernosum was isolated from male New Zealand white rabbits and suspended longitudinally in an organ bath. The corporal strips were precontracted with phenylephrine, tetraethylammonium (TEA) or potassium chloride, and their responses to electrical field stimulation (EFS) or exogenously-administered acetylcholine were examined. EFS caused a frequency-dependent relaxation of the corpus cavernosum precontracted with phenylephrine, which was significantly inhibited or abolished in the presence of procaine (3.5 x 0.0001mol/L) or ouabain (0.0001mol/L). The corporal preparation precontracted with TEA also showed a frequency-dependent relaxation, however, the degree of which was lower than that precontracted with phenylephrine. EFS was without a significant effect on the corporal preparation precontracted with KCl (3 x 0.01mol/L). Acethylcholine elicted a concentration-dependent relaxation of the corpus cavernosum, the magnitude of which was significantly diminished in the presence of L-NAME (0.0001 mol/L). The relaxation response to EFS of the corporal preparation precontracted with phenylephrine was significantly attenuated in the presence of L-NAME (0.0001 mol/L), in which the residual relaxation was completely abolished by glibenclamide (0.00001mol/L). The relaxation of the corpus cavernosum in response to EFS was reversed into a contraction by methylene blue (0.0001mol/L) or TEA (0.01mol/L). These results suggest that endothelium-derived relaxing and hyperpolarizing factors released upon neural stimulation mediate the relaxation of the corpus cavernosum. It is also suggested that EDRF activates soluble guanylate cyclase and EDHF does ATP-sensitive potassium channels.