NITRIC-OXIDE AND CYCLIC-NUCLEOTIDES PARTICIPATE IN THE RELAXATION OF DICLOFENAC ON RAT UTERINE SMOOTH-MUSCLE

1. The effect of diclofenac (10-100 mu M) on vanadate-induced contract ion of rat uterus in calcium-free buffer containing EDTA and the modif ication of this response by pertussis toxin (50 mu g/ml), Rp-cAMPS (10 mu M), W-7 (10 and 60 mu M), L-NMMA (10 and 100 mu M) and D-NMMA (100 mu M) has been assessed. The effects of sodium nitroprusside (10 mu M -1mM), 3-morpholinosydnonimine (SIN-1; 0.1-100 mu M), 1H-[1,2,4]oxadia zolo[4,3 a]quinoxaline-1-one (ODQ; 0.1-100 mu M) and 8-BrcGMP (10 mu M to 1 mM) on vandate-evoked contraction were also studied. 2. Diclofen ac produced dose dependent relaxation of vanadate (0.3 mM)-induced con traction (EC50:17.3 +/- 1.8 mu M, n = 11). This effect was significant ly (P<0.05) reduced by pertussis toxin (EC50: 37.4 +/- 4.5 mu M, n = 6 ) and Rp-cAMPS (EC50:36.3 +/- 3.1 mu M, n = 6). 3. The calmodulin inhi bitor W-7 (1-100 mu M) relaxed, in a concentration-dependent way, the vanadate contraction (EC50:67.0 +/- 18 mu M). W-7 (10 and 60 mu M) did not modify the relaxation elicited by diclofenac, which suggests that calmodulin inhibition and the increase of cAMP are two different acti ons of diclofenac. 4. The action of diclofenac was antagonized (P<0.05 ) by L-NMMA (100 mu M) and ODQ (1 and 100 mu M) but not by D-NMMA (100 mu M), which suggests the involvement of NO-synthase in this effect. 5. Sodium nitroprusside (1 mM) relaxed the vanadate contraction by onl y 31.7 +/- 1.04% (n = 7) and SIN-1 by 27.1 +/- 1.2% (n = 6). This sugg ests that, under the present experimental conditions, both NO donors w ere ineffective. However, 8-BrcGMP (EC50:327 +/- 71 mu M, n = 7) relax ed this contraction up to 58.7 +/- 1.89%. Rp-cAMPS (10 mu M) did not m odify the 8-BrcGMP effect. Thus, a partial contribution of cGMP to inh ibitor effect of drugs on rat uterus was possible. 6. The association between L-NMMA plus ODQ, L-NMMA plus Rp-cAMPS and ODQ plus Rp-cAMPS di d not produce more displacement than L-NMMA, Rp-cAMPS or ODQ alone. Th is suggests the involvement of NO and cyclic nucleotides in the relaxa nt effect of diclofenac in rat uterus. (C) 1998 Elsevier Science Inc.