In vivo monitoring of intracellular free calcium changes during uterine activation by prostaglandin F2α and oxytocin

OBJECTIVE: It has been well established that oxytocin (OXT) increases intracellular free calcium ([Ca2+](i)) by targeting both intracellular and extracellular stores, but the mechanisms involved in the increase through activation with prostaglandin F-2alpha (PGF(2alpha)) are still incompletely understood. This stud), was designed to elucidate the source(s) of increased [Ca2+](i) in response to PGF(2alpha) (10(-6) M) or OXT (10(-8) M) administration in the near-term rat myometrium. METHODS: The animals were divided into an in vitro group (n = 8), where the developed tension of uterine strips was assessed, and an in vivo group (h = 5), where a lobe of the uterus with intact innervation and circulation was loaded with the fluorescent indicator Indo-1 AM to assess [Ca2+](i). RESULTS: PGF(2alpha) and OXT induced a 30.1% and 35.9%, respectively, increase in developed tension in the potassium chloride-depolarized myometrial strips. Nifedipine reduced the PGF(2alpha) and OXT increased tension by 6.5.8% and 49.4%, respectively. in vivo, both PGF(2alpha) and OXT increased [Ca2+](i) in the potassium chloride-depolarized uterine muscle by 35.7% and 44.6%, respectively, increases similar to the rises in tension in vitro. Nifedipine reduced these effects of PGF(2alpha)and OXT by 5.3% anti 39.6%. CONCLUSION: These findings indicate that in near-term myometrium the source of increased [Ca2+](i) after administration of PGF(2alpha) sinular to OXT, is both extracellular and intracellular. Copyright (C) 2002 by the Society for Gynecologic Investigation.