ABSTRACT
<p><b>OBJECTIVE</b>To observe and compare the effects of 17beta-estradiol (EST) on the phasic and tonic contractile activities of the uterine smooth muscles of SD rats in vitro.</p><p><b>METHODS</b>Different concentrations of 17beta-estradiol were added into the perfusion muscular sockets containing uterine smooth muscles of SD rats, and the activities of muscle contraction were recorded at the same time.</p><p><b>RESULTS</b>17beta-estradiol had obvious depression effects on spontaneous rhythmic contraction of the uterine smooth muscles in a concentration-dependent manner, it could considerably decrease muscular tension, the mean amplitudes and frequencies of contractile waves (P < 0.01); it could also suppress the uterine contraction stimulated by KCl, CaCl2 or prostaglandin F2alpha (PGF2alpha). Based on the contraction of uterine smooth muscle stimulated by KCl, IC50 was 7.278 micromol/L and pD2 was -0.862 when calculated by linear regression method. 17beta-estradiol could also inhibit the maximal CaC12 contraction of uterine smooth muscle in the Ca2+ free Krebs solution, which the ECQ was 1.422 x 10(-3) mol/L, pD2 was 2.847 (control), but the E50 was 3.028 x 10(-3) mol/L, p2 was 2.519 (added with EST) when calculated by linear regression method.</p><p><b>CONCLUSION</b>The depression effects of 17beta-estradiol on the spontaneous rhythmic contraction and activated contraction of the uterine smooth muscles of SD rats could be mediated through the blockage of C2+ influx through potential-dependent Ca2+ channels of plasma membrane.</p>