Effects of plant extract neferine on cyclic adenosine monophosphate and cyclic guanosine monophosphate levels in rabbit corpus cavernosum in vitro.

AIM To further investigate the relaxation mechanism of neferine (Nef), a bis-benzylisoquinoline alkaloid extracted (isolated) from the green seed embryo of Nelumbo nucifera Gaertn in China, on rabbit corpus cavernosum tissue in vitro. METHODS The effects of Nef on the concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in isolated and incubated rabbit corpus cavernosum tissue were recorded using 125I radioimmunoassay. RESULTS The basal concentration of cAMP in corpus cavernosum tissue was 5.67 +/- 0.97 pmol/mg. Nef increased the cAMP concentration in a dose-dependent manner (P < 0.05), but this effect was not inhibited by an adenylate cyclase inhibitor (cis-N-[2-phenylcyclopentyl]azacyclotridec-1-en-2-amine, MDL-12, 330A) (P > 0.05). The accumulation of cAMP induced by prostaglandin E1 (PGE1, a stimulator of cAMP production) was also augmented by Nef in a dose-dependent manner (P < 0.05). The basal concentration of cGMP in corpus cavernosum tissue is 0.44 +/- 0.09 pmol/mg. Nef did not affect this concentration of cGMP, either in the presence or in the absence of a guanyl cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ) (P > 0.05). Also, sodium nitroprusside (SNP, a stimulator of cGMP production)-induced cGMP production was not enhanced by Nef (P > 0.05). CONCLUSION Nef, with its relaxation mechanism, can enhance the concentration of cAMP in rabbit corpus cavernosum tissue, probably by inhibiting phosphodiesterase activity.