Interactions between inducible nitric oxide synthase and cyclooxygenase‐2 in response to ischaemia‐reperfusion of rabbit bladder

Abstract

To investigate the interactions between inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in response to ischaemia-reperfusion (I/R) of rabbit bladder. Rabbit bladders were exposed to 2 h of ischaemia by bilaterally clamping the major arteries entering the bladder and then a subsequent 36 h of reperfusion (I/R) with or without intraperitoneal administration of a selective iNOS inhibitor n-(3-(amynomethyl)benzyl)acetamidine (1400W) or a selective COX-2 inhibitor NS-398 given 1 h before killing. The bladder tissues were processed for isometric tension experiments, enzymatic NOS activitiy, tissue contents of nitrite/nitrate (NO(X) ), cyclic guanosine monophosphate (cGMP) and COX activity determined by prostaglandin E(2) (PGE(2) ) production. iNOS and constitutive NOS (cNOS) activities, NO(X) and PGE(2) contents in the bladder tissues at 36 h after reperfusion were significantly higher than those in the sham group with no significant increase in cGMP. Treatment with 1400W abrogated the increases in iNOS activity and NO(X) as well as PGE(2) without changing cNOS activity. In the tension experiments, a NOS substrate, l-arginine, induced detrusor contraction only in the I/R group, which was inhibited by 1400W or NS-398 but not by a selective soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazole[4,3-a]quinoxalin-1-one (ODQ). 8-Br-cGMP induced detrusor relaxation in the sham and I/R groups. Also, l-arginine increased NO(X) and PGE(2) in the bladder tissues only in the I/R group, which were inhibited by pretreatment with 1400W. While, l-arginine increased cGMP contents in the I/R group and this increase was suppressed by ODQ but not by 1400W. These results show that NO derived from an up-regulation of iNOS after I/R increases COX-2-derived PG via a cGMP-independent mechanism. NO-mediated activation of COX-2 may be an important mechanism for the modulation of bladder function after I/R injury.