In Vivo Monitoring of Intracellular Free Calcium Changes During Uterine Activation By Prostaglandin F_2α and Oxytocin

Abstract

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_2α (PGF_2α) are still incompletely understood. This study was designed to elucidate the source(s) of increased [Ca²⁺]_i in response to PGF_2α (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 (n = 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_2α 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_2α and OXT increased tension by 65.8% and 49.4%, respectively. In vivo, both PGF_2α and OXT increased [Ca²⁺]_i in the pottassium 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_2α and OXT by 45.3% and 39.6%.

Conclusions

These findings indicate that in near-term myometrium the source of increased [Ca²⁺]_i after administration of PGF_2α, similar to OXT, is both extracellular and intracellular.