In vivo monitoring of intracellular free calcium changes during uterine activation by prostaglandin f(2alpha) and oxytocin.
OBJECTIVE
It has been well established that oxytocin (OXT) increases intracellular free calcium ([Ca(2+)](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 study was designed to elucidate the source(s) of increased [Ca(2+)](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 (n= 5), where a lobe of the uterus with intact innervation and circulation was loaded with the fluorescent indicator Indo-1 AM to assess [Ca(2+)](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 65.8% and 49.4%, respectively. In vivo, both PGF(2alpha) and OXT increased [Ca(2+)](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 45.3% and 39.6%.


CONCLUSIONS
These findings indicate that in near-term myometrium the source of increased [Ca(2+)](i) after administration of PGF(2alpha), similar to OXT, is both extracellular and intracellular.
Ruttner
Zoltan
Z
Semmelweis University, Faculty of Medicine, Institute of Human Physiology and Clinical Experimental Research, Budapest, Hungary. ruttner@elet2.sote.hu
Ivanics
Tamas
T
Slaaf
Dick W
DW
Reneman
Robert S
RS
Toth
Andras
A
Ligeti
Laszló
L
D000818:Animals; D002118:Calcium / Q000032:analysis*; D015237:Dinoprost / Q000494:pharmacology*; D005260:Female; D005456:Fluorescent Dyes; D007424:Intracellular Fluid / Q000737:chemistry; D015759:Ionomycin / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D009543:Nifedipine / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology*; D011189:Potassium Chloride / Q000008:administration & dosage / Q000494:pharmacology; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D014590:Uterine Contraction / Q000187:drug effects; D014599:Uterus / Q000737:chemistry* / Q000187:drug effects* / Q000648:ultrastructure
D005456:Fluorescent Dyes; D010121:Oxytocin; D015759:Ionomycin; D011189:Potassium Chloride; D015237:Dinoprost; D009543:Nifedipine; D002118:Calcium