OBJECTIVESTo study the relaxation effects of tetrandrine on the corpus cavernosum tissue of rabbit in vitro.

METHODS1. The fluctuation of the dose-response relaxation curves for the contraction of KCl induced by tetrandrine was observed with isolated rabbit corpus cavernosum tissue. 2. Isolated strips of rabbit corpus cavernosum tissue were precontracted with 10 mumol/L phenylephrine(PE). Relaxation in response to cumulative doses of tetrandrine was determined in the absence and presence of nitric oxide synthase inhibitor (L-NNA) and soluble guanylate cyclase inhibitor (methylthioninium).

RESULTS1. The dose-response curves of KCl were shifted to the right nonparallelly, and the maximal responses were depressed to (73.0 +/- 3.8)% and (41.5 +/- 3.4)%, respectively, in the presence of tetrandrine(10 mumol/L, 30 mumol/L). 2. On rabbit cavernosal muscle stripes precontracted with PE(10 mumol/L), increasing concentrations of tetrandrine (1 mumol/L, 10 mumol/L, 30 mumol/L and 100 mumol/L) showed dose dependent relaxation [(6.0 +/- 1.4)%, (21.3 +/- 2.2)%, (47.4 +/- 3.3)%, and (68.1 +/- 3.6)%, P < 0.01]. However, in the meantime, it was found that these relaxation effects were not affected by the presence of L-NNA and methylthioninium (P > 0.05).

CONCLUSIONSTetrandrine was effective in relaxing rabbit corpus cavernosum tissue in vitro in a dose-dependent style. The mechanism might be related with its blocking effect on calcium channel, but not the NO-cGMP passage.