Varying response to luteinizing hormone of two luteal cell types isolated from bovine corpus luteum

Luteal cell suspensions obtained by enzymatic digestion of pregnant cow corpus luteum were found to be heterogenous and mainly made up of two types of cells of different sizes. The large cells (37 micrometers, average diameter) could be separated from the small ones (18 micrometers, average diameter) by sedimentation at unit gravity in a gradient of Ficoll-bovine serum albumin. A comparative in-vitro study of the synthesis of progesterone by the two types of cells indicated striking differences between them. The average content and the synthesis of progesterone in the absence and presence of a saturating dose of bovine LH after incubation for 2 h were 0.07, 0.12 and 6.9 pg/cell for the small cells and 0.65, 2 and 10 pg/cell for the large ones. Moreover, the sensitivity to low concentrations of LH was 100 to 1000 times higher for the small cells than for the large ones. Oestradiol-17 beta at concentrations ranging from 5 X 10(-10) to 5 X 10(-4) mol/l exerted a dose-dependent inhibition on the stimulation of LH in both cell types. These results suggest a possible involvement of both cell types in the synthesis of progesterone in vivo with a greater contribution by the small cells to stimulation induced by LH. Moreover, it appears that small cell suspensions could be a useful model system for in-vitro studies of the control of the synthesis of progesterone in cow corpus luteum.

Effect of danazol on estradiol-17beta and progesterone secretion by porcine ovarian cells in vitro

The effect of danazol on progesterone (P4) and estradiol-17 beta (E2) secretion by cultured porcine granulosa cells was studied. Danazol markedly inhibited both basal and luteinizing hormone (LH)-stimulated P4 secretion by both granulosa and luteal cells in a dose-dependent manner during 24 hour culture periods. E2 secretion by granulosa cells was low (less than 3 ng/mg of protein) when cultured in the absence of an exogenous aromatizable substrate but was markedly increased when testosterone (T) was added to the media. Danazol inhibited E2 secretion by granulosa cells only when cultured in the presence of testosterone. E2 secretion by luteal cells was low even in the presence of testosterone and was not affected by danazol. These findings support the hypothesis that danazol can directly inhibit ovarian steroidogenesis independently of its inhibitory action on gonadotropin secretion.

Estradiol inhibition of luteinizing hormone-stimulated progesterone synthesis in isolated bovine luteal cells

The effects of several steroid hormones on progesterone synthesis and cAMP accumulation in isolated bovine corpora luteal cells were investigated in an attempt to determine if any of the steroids would affect the basal level of these processes or their response to gonadotropin. Isolated bovine corpora luteal cells responded to LH with a significant (P less than 0.05) increase in progesterone synthesis and cAMP accumulation when incubated at 37 C for up to 1 h. Exogenous cAMP and analogs of cAMP also significantly stimulated steroidogenesis in these incubated cells. Stimulation of progesterone synthesis by 1 microgram/ml LH was significantly suppressed (P less than 0.05) in the presence of 5--10 microgram/ml estradiol. This inhibition appeared to be largely specific for 17beta-estradiol, in that other steroids such as estrone, estriol, 17alpha-estradiol, cortisol, and dihydrotestosterone were not inhibitory. Testosterone was found to be inhibitory, but it is uncertain if this effect was due to the androgen itself or to its conversion to estradiol. Estradiol did not affect the increase in endogenous cAMP caused by LH in these cells, but did inhibit the effect of exogenous dibutyryl cAMP on progesterone synthesis. The magnitude of this inhibition of the effect of dibutyryl cAMP was not, however, equal to the estradiol inhibition of the stimulation of progesterone synthesis by LH. These data indicate that estradiol, a possible physiological luteolytic agent, has a direct inhibitory action on the corpus luteum and produces its suppression by blocking the stimulatory effect of LH at a step after cAMP.

Receptor regulation and target cell responses: studies in the ovarian luteal cell

Studies of hormone-induced 'desensitization' in the luteinized rat ovary show that changes in receptor number and adenylate cyclase at the cell surface result in an altered biological effect of luteinizing hormone on progesterone production. The sensitivity of these effects to changes in gonadotropin levels suggests that receptor turnover or processing is involved in the normal mechanism of hormone action.

Control of cellular proliferation by the fibroblast and epidermal growth factors

Recent studies on the effect of the fibroblast and epidermal growth factors (FGF and EGF, respectively) on the proliferation of ovarian cells and vascular endothelial cells are reviewed. During the ovarian cycle, luteal cells are derived from granulosa cells by a process of cytomorphosis. These two cell types thus allow a study of the changes that occur in growth control when one cell type is converted into another. Also described is the control of vascular endothelial cell proliferation by FGF (but not by EGF). We discuss the effects of FGF and EGF on cells derived from the embryonic ectoderm, mesoderm, and endoderm and examine the hypothesis that cellular specificity for various growth factors is conferred during embryo development. Finally, since antagonists of growth factors are probably as important as the mitogens in the overall control of cell proliferation, we review certain mechanisms and agents through which the mitogenic effect of FGF can be repressed, i.e., cell-cell interaction at confluence, trophic hormones, and a diffusible factor(s) from cartilage.

Effects of fibroblast and epidermal growth factors on ovarian cell proliferation in vitro. II. Proliferative response of luteal cells to FGF but not EGF

The effect of fibroblast growth factor (FGF) and epidermal growth factor (EGF) on luteal cell proliferation in vitro has been examined. Luteal cells maintained in the presence of low serum (1%) go through a doubling after 7 days. Addition of EGF induced one more doubling of the cells, after which the cells became resting. In contrast, FGF induced the cells to divide logarithmically with a cell cycle of 48 h. The effect of FGF was dependent on the serum and FGF concentrations. It has been obtained with serum concentrations ranging from 0.1% to 10% and with FGF concentrations ranging from 0.1 ng to 10 ng/ml. The half-maximal FGF response was observed at 1.5 x 10(-11)M. In contrast, EGF has no effect besides causing an initial cell doubline within the same range of serum or FGF concentrations. Since granulosa cells have been shown to be highly sensitive to EGF as well as FGF, it can be concluded that during the luteinization process that sensitivity of the cells to EGF is lost, while the sensitivity of FGF is retained. This demonstrates that although luteal cells and granulosa cells are interrelated cell types their sensitivity to growth factors such as EGF is quite different.

A possible interrelationship between gonadotrophin stimulation and prostaglandin F2alpha inhibition of steroidogenesis by granulosa-luteal cells in vitro

The newly formed corpus luteum of many species is refractory to the lytic action of prostaglandin F2alpha (PGF2alpha). This phenomenon was studied utilizing porcine, bovine and human granulosa-luteal cells in tissue culture. The steroidogenic potential of the granulosa-luteal cells was critical in determining whether PGF2alpha could inhibit progesterone production. Since the steroidogenic potential of the granulosa-luteal cell is related to the amount of LH bound to the cell, the bound LH may protect the granulosa-luteal cells from the lytic action of PGF2alpha. Finally, a 'see-saw' type of interaction between LH and PGF2alpha is postulated to account for the resistance of the newly formed corpus luteum to PGF2alpha.

Luteal cell receptor content for prolactin (PRL) and luteinizing hormone (LH): regulation by LH and PRL

The effect of LH and PRL during the differentiation of granulosa cells to luteal cells was examined by determining the ability of LH and PRL to regulate luteal cell receptor content for these hormones and to increase production of progesterone. Preovulatory follicles and corpora lutea were hormonally induced in immature hypophysectomized female rats by sequential treatment with estradiol, hFSH and oLH. The content of receptor for LH was high in granulosa cells of large antral follicles. Administration of LH caused receptor for LH to decrease markedly within 24 h and to remain low for 96 h. In contrast, granulosa cell content of receptor for PRL increased progressively for 48 h following LH stimulation and remained elevated in fully luteinized cells at 96 h. This increase in PRL receptor appears to be functionally related to the ability of luteal cells to respond to PRL. When PRL was given for 4 days after LH, both luteal cell progesterone production and LH receptor content increased progressively after, but not before, 48 h. Since these changes occurred in the absence of LH, the increase in LH receptor appears to be a consequence of, but not a requirement for, the PRL-induced increase in progesterone production. If daily injections of PRL were delayed for 72 or 96 h following LH induction of lutenization, luteolytic rather than luteotropic effects of PRL were observed. Since receptor for PRL remained elevated at 72 and 96 h, intracellular mechanisms and not receptor content, appear to be effecting the response of luteal cell to PRL.