The role of exogenous calcium for gonadotropin-stimulated progesterone production by human granulosa-luteal cells

The production of progesterone and 5,6-epoxyeicosatrienoic acid by human granulosa cells

Previous investigations have implicated epoxygenase metabolites of arachidonic acid in the control of steroidogenesis in luteinised granulosa cells. The aim of this study was to assess this hypothesis further. We first determined the responsiveness of the cells in vitro to three different stimuli, namely luteinising hormone (LH), interleukin-1beta (IL-1beta), and dibutyryl cyclic AMP (db. cyclic AMP). Their effects were time-dependent, in that progesterone production from cells incubated for 3 days prior to stimulation responded strongly to db. cyclic AMP, to a lesser extent to LH and not to IL-1beta. After 6 days of preincubation, all three stimuli increased progesterone production, and this preincubation period was used in the remainder of the study.LH and IL-1beta increased the intracellular levels of 5,6-epoxyeicosatrienoic acid (5,6-EpETrE) maximally after 10 min, whereas db. cyclic AMP had a more rapid effect within 2-5 min. There were no changes in levels of 14,15-epoxyeicosatrienoic acid (14,15-EpETrE), indicating that the effect was specific. Levels of dihydroxy derivatives of arachidonic acid were also increased, suggesting rapid metabolism of 5,6-EpETrE to inactive 5,6-DiHETrE. The effects of 5,6-EpETrE on progesterone production were transient, which may be due to the lability of this compound in solution, and limited passage into the granulosa-luteal cell cytoplasm. These results support a role for 5,6-EpETrE in the production of progesterone by human granulosa-luteal cells.

Evidence that basal secretion of relaxin by individual cultured large luteal cells is influenced by mobilization of intracellular calcium: analysis by a reverse hemolytic plaque assay

Ca2+ redistribution from an intracellular site(s) is a key biochemical event associated with relaxin (RLX) secretion by large luteal cells (LLCs) of porcine origin. However, the functional significance of internal stores of Ca2+ to basal rates of RLX secretion is not well understood. In addition, the identity of the intracellular storage site(s) for Ca2+ within LLCs is not known, nor is it clear if all RLX-releasing LLCs are equally dependent on this pool. In the present study, release of RLX from 24 h cultured luteal cells derived from early pregnant swine was monitored by a reverse hemolytic plaque assay (RHPA). Incubation of cultures in the presence of graded concentrations of thapsigargin (1 nM-1 microM), a plant sesquiterpene lactone that inhibits endoplasmic reticulum Ca(2+)-ATPase and thereby increases cytosolic Ca2+ concentrations, resulted in a dose-related increase in basal RLX secretion. The stimulatory effect of thapsigargin on RLX production was not abrogated by culture in Ca(2+)-free medium. Suppression of Ca2+ release from the endoplasmic reticulum of LLCs, achieved by incubating monolayers in medium containing dantrolene (1-100 microM), resulted in dose-related inhibition of basal RLX release. Taken together, these results suggest that the endoplasmic reticulum serves as a major storage site for Ca2+ redistribution within LLCs and, furthermore, that mobilization from this site is functionally coupled to basal secretion of RLX.

Human ovarian granulosa cell culture: determination of blood cell contamination and evaluation of possible culture purification steps

OBJECTIVE

To determine the degree of blood cell contamination in GC preparations; to assess techniques of GC purification; and to determine possible effects of contaminating cells and purification techniques on cultured GC in terms of steroid hormone production.

DESIGN

Contamination of GC by white blood cells was assessed by Wright's stain and immunohistochemistry. Purification was attempted by: (1) Ficoll density centrifugation (to remove polymorphonuclear leukocytes [PML]); (2) incubation in tissue culture plastic dishes (to remove adherent monocyte/macrophages); and (3) incubation in the presence of high salt (to remove lymphocytes).

RESULTS

Ficoll density centrifugation reduced PML to 2% of total cells, incubation in plastic dishes reduced monocyte/macrophage contamination from 6% to 7% down to less than 1%, and high-salt incubation reduced lymphocyte contamination from 10% to 12% down to 4%. Granulosa cells plated after preparation with addition of high salt showed increased progesterone production, which could not be entirely explained by the removal of contaminating lymphocytes.

CONCLUSION

These results indicate that the human GC culture system is more complex than is often assumed, and methods that remove a majority of these white blood cells are presented.

Apolipoprotein E synthesis by cultured human ovarian granulosa cells: regulation by human chorionic gonadotropin and cholesterol

OBJECTIVE

Apolipoprotein E (Apo E) is a surface component of several classes of plasma lipoproteins and functions as a receptor ligand for the low-density lipoprotein (LDL) (B/E) receptor, the hepatic E receptor, and the LDL receptor related protein. In continuing studies of Apo E synthesis by extrahepatic steroidogenic tissue, we have examined Apo E production and its control in cultured human granulosa cells (GC).

DESIGN

Human GC obtained at the time of oocyte aspiration for in vitro fertilization were cultured, and the following parameters were measured: progesterone secretion into the medium, Apo E synthesis and secretion, and Apo E messenger ribonucleic acid (mRNA) content of the GC.

RESULTS

Human chorionic gonadotropin induces a decrease in Apo E protein synthesis and Apo E mRNA content. The addition of aminoglutethimide (which blocks cholesterol conversion to pregnenolone) and/or LDL (which provides the cell with cholesterol), both result in an increase in Apo E protein synthesis and Apo E mRNA content. These latter findings are in agreement with studies in nonsteroidogenic cells, which show that Apo E production is positively correlated with cell cholesterol content.