Motilities Of Isolated Uterine Smooth Muscles Of Rats In Various Phases Of Menstrual Cycle And Interference Research Of Phytoestrogens

BACKGROUND&AIM:The non-pregnant uterus exhibits the wave-like activity throughout the whole estrous cycle which may provide for gamete/embryo transportation through the utero-tubal cavities and successful embryo implantation.Moreover,the endogenous estrogen secretion during estrous cycle possesses a very important modulating effect on the uterine contractile activity.Phytoestrogen is an analogue of estradiol.Though the effects of phytoestrogens in the reproductive system were more and more attracted to the researchers,but the relationship between phytoestrogens and the contractilities of uterine smooth muscles is still unknown.In the present study,we designed to observe the patterns of uterine contractile activity in various phases of menstrual cycle,try to observe and compare the effects of PUE,RES or GEN on the spontaneous and activated contractile activities of uterine smooth muscle within various phases of estrous cycle in vitro;and try to elucidate its underlying mechanisms.METHODS:Adult female Sprague Dawley rats were used in this study.The experimental-consuming rat was stunned before the operation and the whole uterus was quickly removed and the strips were prepared.Isolated strips were suspended in organ chambers containing Kreb’s solution which buffered at pH 7.4 in separate 5mL tissue chambers,bubbled with 95%O2 and 5%CO2.The muscle strips were allowed to equilibrate for at least 30min with a resting tension of 1.5g and the solution was changed every 20min.After equilibration,different concentrations of EST,PUE,RES and GEN were added to the ex-vivo strips,the spontaneous and activated contractility of strips were measured before and after incubation with EST and PUE,RES or GEN,respectively.The spontaneous and stimulated contractile activities of the uterine smooth muscles were measured with force transducers and recorded with the BL-420E+ experimental system of biological function(TME,China)by microcomputer.Some uterine smooth muscle pieces were fixed in the 4%Paraformaldehyde solution,then administered with hematoxylin-eosin staining(HE staining)and paraffin section technique.RESULTS:(1)There were three kinds of uterine contractile traces in different phases of estrous cycle:the tonic contraction,the phasic contraction,and the untypical contraction;(2)The depression of EST,PUE,RES and GEN happened in phasic and PGF2a-inducedcontractile activity,they inhibited the basal tension,mean amplitude and frequencies in a dose-dependent manner;they could also dose-dependently inhibit the tonic contraction induced by high K+;(3)The inhibition of PUE,RES and GEN in the KCl-induced tonic contraction was significantly attenuated by the very selective β2 adrenergic antagonist;ATP-dependent K+ channel blocker Glibenclamide(HB-419),NO synthase inhibitor N-nitro-L-arginine(L-NNA)partly decreased the inhibitory effects of RES or GEN;but the estrogen receptor antagonists tamoxifen(TAM)and ICI182780,and the prostaglandin synthase antagonist indomethacin(IND)failed to alter the inhibitory effects of PUE,RES and GEN;(4)RES and GEN could obviously inhibit the CaCl2-induced trace and move it rightward in Ca2+-free Kreb’s solution with high K+;but PUE had no effect;(5)PUE,RES,and GEN reduced the first contraction induced by oxytocin(OXY),acetylcholine(ACH),and prostaglandin F(PGF2a),but did not change the second contraction caused by CaCl2 in Ca2+-free Kreb’s solution;CONCLUSION:There are three uterine contractile patterns in different phases of estrous cycle.Phytoestrogen PUE,RES and GEN have the similar function with EST,they can inhibit the contractile activity of isolated uterine smooth muscle both at rest and in response to stimulation by KCl,OXY,ACH or PGF2α.For PUE,the mechanisms are responsible for the inhibitory effects probably due to the inhibition ofβ2-adrenoceptor and Ca2+ release from sarcoplasmic reticulum.For RES and GEN,the mechanisms are responsible for the inhibitory effects probably due mainly to βadrenergic receptor,Ca2+ influx through voltage-operated calcium channels(VOCs),Ca2+ release from sarcoplasmic reticulum,the activation of ATP-dependent K+channel,or the NO production.