The effect of oxytocin on hCG action in phosphoinositide turnover in porcine myometrial smooth muscle cells.
The aim of this study was to investigate the effects of hCG, hCG plus oxytocin and oxytocin on [3H] inositol phosphate (IP) formations in porcine myometrial cells obtained from ovariectomized and cyclic gilts. Myometrial cells were treated with radioactive myo-[3H]inositol for 48 hours, washed and pre-incubated with 10 mM LiCl, and then different doses of hCG (10, 100, 1000 mU) were added over 24 h. At the end of the last day of culture some wells were treated with 1 microM oxytocin for 30 min. The highest production of total inositol phosphates (d.p.m.) was found in cells from ovariectomized gilts given in vivo estradiol benzoate and progesterone for five consecutive days and treated with 1000 mU hCG and 100 mU hCG plus 1 microM oxytocin (984 +/- 84 and 1063 +/- 131 vs 314 +/- 36, respectively). There was also a very significant increase of IP1 after the addition of 1000 mU hCG (p < 0.001) and IP1 and IP3 when 1000 mU hCG plus oxytocin were added (p < 0.001 and p < 0.01, respectively). Myometrial cells harvested from ovariectomized, untreated in vivo, gilts did not respond to both oxytocin and hCG in vitro. Only oxytocin alone increased the formation of IPs in cells from ovariectomized pigs treated with estradiol in vivo (p < 0.01). Myometrial cells obtained from cyclic pigs during the luteal and follicular phases of the estrous cycle responded to lower doses of hCG (10 mU), causing significant production of IPs (p < 0.05). The highest dose of hCG plus oxytocin provoked accumulation of total [3H]inositol phosphate (p < 0.05) 53% over the basal level on days 21/1 of the estrous cycle. The present study demonstrates that hCG and oxytocin can increase the accumulation of inositol phosphates in porcine myometrial cells. However, this formation is dependent on the steroid hormone status of animals.
Kisielewska
J
J
Division of Reproductive Endocrinology and Phathophysiology, Polish Academy of Sciences, Olsztyn, Poland.
Ziecik
A J
AJ
D000818:Animals; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010121:Oxytocin / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011869:Radioligand Assay; D013552:Swine
D006063:Chorionic Gonadotropin; D010716:Phosphatidylinositols; D010121:Oxytocin