The effects of neocuproine and bathocuproine, Cu(I) and Cu(II) chelators, respectively, were studied on relaxations in response to electrical field stimulation, acetylcholine, S-nitrosoglutathione, acidified sodium nitrite and sodium nitroprusside in the mouse corpus cavernosum precontracted with phenylephrine. Neocuproine significantly inhibited relaxations induced by electrical field stimulation, acetylcholine and S-nitrosoglutathione, but not by acidified sodium nitrite and sodium nitroprusside. The pre-prepared neocuproine-Cu(I) complex was ineffective on the responses. The discrepancy between the shape of relaxations in response to electrical field stimulation or to acetylcholine and S-nitrosoglutathione was abolished by adding CuCl2 into the bathing medium. The copper action was blocked by neocuproine but not by bathocuproine. However, the pre-prepared bathocuproine-Cu(II) complex did not accelerate the relaxations affected by CuCl2. These findings suggest that a Cu(I)-dependent mechanism may play a role in the relaxation induced by the endogenous relaxant factor as well as by S-nitrosoglutathione in mouse cavernosal tissue. (C) 2000 Elsevier Science B.V. All rights reserved.