Properties of endothelin-induced contractions in the rabbit non-pregnant and pregnant myometria.
Endothelin produced concentration-dependent contractions in both non-pregnant and pregnant myometria. These contractions consisted of two components; rhythmic and slowly developing contractions. The rhythmic contractions were abolished by calcium channel antagonists and in calcium-free Krebs-Ringer solution. On the contrary, the slowly developing contraction was little affected by calcium channel antagonists, and considerably reduced in calcium-free Krebs-Ringer solution. These results indicate that the rhythmic contractions are dependent on extracellular calcium and mediated via calcium influx through voltage-dependent calcium channel, and that the slowly developing contraction is dependent on another mechanism than extracellular calcium influx and may be due to the release of calcium from intracellular calcium-stores. Endothelin was more potent in the non-pregnant myometrium than in the pregnant one (-log EC50 (M) values were 9.07 +/- 0.11 in the non-pregnant and 8.41 +/- 0.06 in the pregnant, respectively). In the presence of calcium channel antagonists and in calcium-free Krebs-Ringer solution, endothelin-induced contractions in the non-pregnant myometrium were more markedly depressed than those in the pregnant one. These findings suggest that endothelin receptors exist in rabbit myometrium, and that a functional change at the level of endothelin receptors, the calcium channels to regulate extracellular calcium influx or calcium mobilizing system from intracellular calcium-stores may occur in accordance with being pregnant.
Suzuki
Y
Y
Department of Obstetrics & Gynecology, Fukushima Medical College, Japan.
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016232:Endothelins / Q000494:pharmacology*; D005260:Female; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000032:analysis; D017466:Receptors, Endothelin; D014590:Uterine Contraction / Q000187:drug effects*
D002121:Calcium Channel Blockers; D016232:Endothelins; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin