Gestational changes in oxytocin- and endothelin-1-induced contractility of pregnant rat myometrium.
The mechanical effects of KCl, oxytocin and endothelin-1 on pregnant rat myometrium were examined using intact strips and beta-escin-treated skinned strips. Myometrial tissues from delivering rats were more sensitive to 10.7 mM K+ compared to mid and late gestation. Maximum contractions induced by K+ were obtained at concentrations of 118 mM at mid and late gestation and during delivery. The maximum amplitude of contractions induced by oxytocin and endothelin-1 compared to the 118 mM K(+)-induced contraction increased during the progress of gestation. Maximum contractions induced by oxytocin and endothelin-1 were greater than those induced by 118 mM K+ at delivery, and maximum contractions by oxytocin were larger than those by endothelin-1 during delivery. In 10 microM nifedipine and Ca(2+)-free (containing 2 mM EGTA) solutions, 118 mM K+ contractions were completely abolished; however, both oxytocin and endothelin-1 produced contractions. In Ca(2+)-free solutions, contractions by oxytocin were larger than those by endothelin-1. In skinned myometrial strips, guanosine 5'-O-thiotriphosphate (GTP, 1 microM-1 mM), guanosine 5'-O-(gamma-thiotriphosphate) (GTP gamma S, 0.1-100 microM) and oxytocin (1 nM-0.1 microM) with 10 microM GTP, but not endothelin-1 with 10 microM GTP increased Ca2+ sensitivity of contractile force.(ABSTRACT TRUNCATED AT 250 WORDS)
Izumi
H
H
Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston 77555-1062, USA.
Byam-Smith
M
M
Garfield
R E
RE
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D016232:Endothelins / Q000494:pharmacology*; D004928:Escin / Q000494:pharmacology; D005260:Female; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007743:Labor, Obstetric / Q000502:physiology; D009215:Myometrium / Q000187:drug effects* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014590:Uterine Contraction / Q000187:drug effects*; D014700:Verapamil / Q000494:pharmacology
D016232:Endothelins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010121:Oxytocin; D004928:Escin; D006160:Guanosine Triphosphate; D014700:Verapamil; D009543:Nifedipine; D011188:Potassium; D002118:Calcium