Effect of oxytocin on free intracellular Ca2+ levels and progesterone release by human granulosa-lutein cells.

Abstract

Oxytocin and its receptor are found in the corpus luteum in a variety of species, including the human.In the present study we used fura- T HE SYNTHESIS of oxytocin in the corpus luteum of the ovary is well established and occurs in a variety of species (l-3; for review, see Ref. 4), including the human (5-8). Moreover, indirect evidence for the presence of oxytocin receptors in human granulosa-lutein cells was provided by a study that showed inhibitory effects of oxytocin on FSHstimulated estradiol secretion (9). Using microdialyzed human corpora lutea, paracrine effects of oxytocin on steroid production were reported. Oxytocin stimulated both progesterone and estradiol release in the young human corpora lutea examined (10). Besides these reports, which give indirect evidence for functional oxytocin receptors in the human ovary, more recently their presence was proven by the detection of oxytocin receptor mRNA in the human ovary (11). However, the signal transduction pathway of the oxytocin receptor in the human corpus luteum has not been examined, and there is no information available concerning whether the expression of oxytocin receptors changes during differentiation. We, therefore, tried to address these points in the present study. We investigated whether activation of oxyto- tin receptors can cause elevations of intracellular free calcium concentrations in human granulosa-lutein cells in a manner similar to that we reported previously in cultured human myometrial cells (12) and rat pituitary corticotrophs (13,14). In addition, we examined the role of oxytocin in progesterone release, and the effect of hCG exerted on the release of oxytocin by cultured human granulosa-lutein cells. Materials and Methods Materials ABSTRACTOxytocin and its receptor are found in the corpus luteum in a variety of species, including the human. In the present study we used fura-2 microfluorimetry to investigate whether activation of the oxytocin receptor of cultured human granulosa-lutein cells causes intracellular calcium (Ca 2 +) signals and affects progesterone release. Although after 1 day in culture, ceHs were not responsive to oxytocin, the number of responsive cells increased steadily during the first 3 days in culture, reaching a maximum on days 4 and 5 (59-66%) and then declined again until day 8. Effective oxytocin concentrations were apparently independent of the culture day, and concentrations as low as 10 nmoljL increased intracellular free Ca 2 + levels from 70-140 nmol/L (basal levels) to maximal peak levels of 800 nmoljL. The oxytocin-induced Ca 2 + signal was not affected by removal of extraceHular Ca 2 + with EGTA. Moreover, depletion of intracellular Ca 2 + stores by ionomycin treatment rendered the cells unresponsive to oxytocin, pointing also at the intraceHular source of the oxytocin-inducible Ca

Human Luteinized Granulosa Cells—A Cellular Model for the Human Corpus Luteum

“…It was hypothesized to act locally, e.g., as a luteolytic factor (31–33), because local production was accompanied by expression of the OT receptor (OTR) (34–36). Two studies in human mural GCs built on these results (37, 38) and confirmed expression of the receptor in GCs and CL. Exogenously applied to human GCs, OT acutely within seconds elevated the levels of intracellular Ca 2+ and within hours, changed progesterone production (37).…”

“…Two studies in human mural GCs built on these results (37, 38) and confirmed expression of the receptor in GCs and CL. Exogenously applied to human GCs, OT acutely within seconds elevated the levels of intracellular Ca 2+ and within hours, changed progesterone production (37). A further downstream role of OT in the induction of apoptosis of GCs became apparent in a follow-up study, also employing IVF-derived GCs.…”

The NADPH oxidase 4 is a major source of hydrogen peroxide in human granulosa-lutein and granulosa tumor cells

“…The stimulation protocols (i.e. the “long” protocol), were described 9,10,41–44 . The ethics committee of the Ludwig-Maximilians University Munich approved the use of follicular aspirates and GCs for scientific experiments (Project 323-05).…”

Large conductance voltage-and calcium-activated K+ (BK) channel in health and disease

“…The K Ca channels play a role in producing sex steroid hormones that are induced by gonadotropins (Kim et al, 2020). The involvement of BK channels in intracellular calcium signaling and progesterone release in luteinizing GCs emphasizes the importance of these channels in the control of female reproductive hormones (Mayerhofer et al, 1993).…”