Role of opioid and nitric oxide systems in the nonadrenergic noncholinergic-mediated relaxation of corpus cavernosum in bile duct-ligated rats.

Changes in nonadrenergic noncholinergic (NANC)-mediated relaxation of the anococcygeus muscle have been demonstrated in cholestasis. Cholestasis is also associated with accumulation of endogenous opioid peptides and nitric oxide (NO) overproduction. This study was therefore undertaken to investigate the effect of cholestasis on the NANC-mediated relaxation of corpus cavernosum in bile duct-ligated rats and to examine the possible roles of the opioid system and nitric oxide in the cholestasis-associated alterations of corpus relaxation. Bile duct-ligated and sham-operated rats were treated for 2 weeks with either normal saline, N (omega)-nitro L-arginine methylester (L-NAME) (3 mg/kg/day, i.p.) or naltrexone (20 mg/kg/day, i.p.). On the 14th day, the strips of corpus cavernosum were mounted under tension in a standard oxygenated organ bath with guanethidine sulfate (5 microM) and atropine sulfate (1 microM) (to produce adrenergic and cholinergic blockade). The strips were precontracted with phenylephrine hydrochloride (7.5 microM) and electrical field stimulation was applied at different frequencies to obtain NANC-mediated frequency-dependent relaxant responses. The results showed that the amplitudes of relaxation responses at each frequency in bile duct-ligated rats were greater than the responses of sham-operated animals. This increase in relaxation responses in bile duct-ligated rats was inhibited by chronic L-NAME administration for 2 weeks so it seemed that it might be due to the nitric oxide overproduction in cholestatic states. Chronic administration of naltrexone for 2 weeks to bile duct-ligated rats had the same inhibitory effect on the relaxation responses. Our results demonstrated that in cholestasis, there was an increase in NANC-mediated relaxation of corpus cavernosum and both opioid and nitric oxide systems were involved in this increase.