Hormonal effects on the contractile apparatus of the myometrium.
The effect of estradiol-17 beta (E2) and progesterone (P) on the structure of myofilaments of the smooth muscle of the myometrium of cats was studied by electron microscopy. Animals which had been ovariectomized for at least four weeks were divided into three treatment groups. Group I received no additional treatment. Group II animals were treated for 14 days with E2, and Group III animals were treated for 14 days with E2 and then with E2 and P. The smooth muscle of the uterus of Group I animals displayed a single array of thin (less than 10nm) filaments only. Group II animals displayed in all cases a double array of thick (14-16 nm) filaments, whereas Group III exhibited a single array of thin (6-8 nm) filaments only. These results suggest that E2 induces assembly of thick filaments in ovariectomized cats while P promotes thick filament disassembly. It is suggested that this alteration of the structure of the thick filament may be involved in the mechanism by which these hormones alter the contractile activity of the myometrium during estrus, pregnancy, and at parturition.
D000818:Animals; D002369:Castration; D002415:Cats; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D008854:Microscopy, Electron; D009215:Myometrium / Q000187:drug effects* / Q000648:ultrastructure; D011374:Progesterone / Q000494:pharmacology*; D014590:Uterine Contraction / Q000187:drug effects*; D014599:Uterus / Q000187:drug effects*
D011374:Progesterone; D004958:Estradiol