Nitric oxide and cyclic nucleotides participate in the relaxation of diclofenac on rat uterine smooth muscle.

1. The effect of diclofenac (10-100 microM) on vanadate-induced contraction of rat uterus in calcium-free buffer containing EDTA and the modification of this response by pertussis toxin (50 micrograms/ml), Rp-cAMPS (10 microM), W-7 (10 and 60 microM), L-NMMA (10 and 100 microM) and D-NMMA (100 microM) has been assessed. The effects of sodium nitroprusside (10 microM-1 mM), 3-morpholinosydnonimine (SIN-1; 0.1-100 microM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ; 0.1-100 microM) and 8-BrcGMP (10 microM to 1 mM) on vandate-evoked contraction were also studied. 2. Diclofenac produced dose-dependent relaxation of vanadate (0.3 mM)-induced contraction (EC50:17.3 +/- 1.8 microM, n = 11). This effect was significantly (P < 0.05) reduced by pertussis toxin (EC50: 37.4 +/- 4.5 microM, n = 6) and Rp-cAMPS (EC50:36.3 +/- 3.1 microM, n = 6). 3. The calmodulin inhibitor W-7 (1-100 microM) relaxed, in a concentration-dependent way, the vanadate contraction (EC50:67.0 +/- 18 microM). W-7 (10 and 60 microM) did not modify the relaxation elicited by diclofenac, which suggests that calmodulin inhibition and the increase of cAMP are two different actions of diclofenac. 4. The action of diclofenac was antagonized (P < 0.05) by L-NMMA (100 microM) and ODQ (1 and 100 microM) but not by D-NMMA (100 microM), which suggests the involvement of NO-synthase in this effect. 5. Sodium nitroprusside (1 mM) relaxed the vanadate contraction by only 31.7 +/- 1.04% (n = 7) and SIN-1 by 27.1 +/- 1.2% (n = 6). This suggests that, under the present experimental conditions, both NO donors were ineffective. However, 8-BrcGMP (EC50:327 +/- 71 microM, n = 7) relaxed this contraction up to 58.7 +/- 1.89%. Rp-cAMPS (10 microM) did not modify the 8-BrcGMP effect. Thus, a partial contribution of cGMP to inhibitor 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 did not produce more displacement than L-NMMA, Rp-cAMPS or ODQ alone. This suggests the involvement of NO and cyclic nucleotides in the relaxant effect of diclofenac in rat uterus.