PARTIAL CONTRIBUTION OF POLYAMINES TO THE RELAXANT EFFECT OF 17-ALPHA-ESTRADIOL IN RAT UTERINE SMOOTH-MUSCLE

1. The effects of 17 alpha-estradiol on KCl (60 mM), CaCl2 (30 mu M to 10 mM) and vanadate (0.3 mM)-induced contractions in rat uterus have been assayed. Furthermore, the effect of 17 alpha-estradiol on calmodu lin-stimulated cAMP-phosphodiesterase activity was also studied. 2. 17 alpha-estradiol relaxed the tonic contraction induced by KCI (60 mM) in a concentration dependent way (IC50, 8.3+/-0.7 mu M), and CaCl2 (0. 1 to 10 mM) counteracted it. 3. CaCl2 (30 mu M to 10 mM) produced conc entration-dependent contraction of rat uterus in a calcium-free medium supplemented with 60 mM of KCl (EC50: 0.2+/-0.01 mM). 17 alpha-estrad iol (8 mu M) antagonized the contraction induced by CaCl2, increasing the EC50 value up to 0.7+/-0.1 mM (P<0.01). 4. 17 alpha-estradiol (0.1 to 1 mM) relaxed in a concentration dependent way the tonic contracti on induced by vanadate in rat uterus incubated in a calcium-free mediu m and EDTA supplemented. The maximal relaxation achieved with I mM of 17 alpha-estradiol was 52.2+/-2.8%. 5. 17 alpha estradiol (1 to 100 mu M) did not modify the basal activity of cAMP phosphodiesterase but in hibited the calcium plus calmodulin stimulated activity. The maximal i nhibition achieved was 43+/-5.4%. 6. The relaxing effect of 17 alpha-e stradiol on KCI (60 mM)-induced tonic contraction was unmodified with the antioestrogen tamoxifen (0.1 and 1 mu M), the inhibitor of tirosin e kinase (genistein, 10 mu M) and the cAMP-dependent protein kinase in hibitor (Rp-adenosine 3',5'-monophosphothioate, triethylamine salt, 10 0 mu M) However, the effect was antagonized with the inhibitor of tran scription (actinomycin D, 5 mu g/ml,), the inhibitor of protein synthe sis (cycloheximide, 10 and 100 mu g/ml), and the inhibitor of ornithin e decarboxilase (a-difluoromethyl-ornithine, 10 mM). 7. Our results su ggest that polyamines contribute to the relaxant effect of 17 alpha-es tradiol in rat uterine smooth muscle behaving, presumably, as mediator s of the transcriptional component involved in the effect of 17 alpha- estradiol. (C) 1998 Elsevier Science Inc.