Steroidogenic activity, insulin-like growth factor-I production, and proliferation of granulosa and theca cells obtained from dominant preovulatory and nonovulatory follicles during the bovine estrous cycle: effects of low-density and high-density lipoproteins

A dietary supplement of calcium soaps of fatty acids enhances luteal function in sheep

The effect of a dietary supplement of calcium soaps of fatty acids on luteal steroidogenic activity was studied in sheep. Mature 3- to 5-year-old North Country Cheviot ewes were given either a pelleted control diet (C; grass, beet pulp, barley; no. = 15) providing daily, 29⋅8 g nitrogen and 13⋅7 MJ of metabolizable energy (ME) or the same diet with 5% (w/w) of the ingredients replaced with protected lipid (C + CaFA; calcium soaps of fatty acids, Megalac, Volac Etd; no. = 15) for 21 days. The latter diet provided daily 30⋅2 g nitrogen and 15⋅9 MJ ME. At the end of the feeding period the ewes were slaughtered and blood samples and ovaries were collected from individual animals. The numbers of large- (≤ 4 mm diameter) and small- to medium-sized (1 to 3 mm diameter) follicles were recorded and follicular fluids from both size groups were stored for later analyses following centrifugation. Each mature corpus luteum (CL) was isolated from its ovary and sliced to provide a pair of ca. 0⋅3 mm diameter sections. These sections (mean = 163 (s.e.12) mg) were cultured separately (4 h; 39°C; 5% CO2) in 3 ml Medium 199 in the absence or presence of 100 μIU LH. Dietary supplementation of calcium soaps of fatty acids increased progesterone concentrations in the plasma (P < 0⋅05) and follicular fluid (P < 0⋅01 and P < 0⋅05 for large and small to medium follicles, respectively); trigylcerides in plasma (P < 0⋅05); total cholesterol in plasma (P < 0⋅001) and follicular fluid (P < 0⋅001); HDL-cholesterol in plasma (P < 0⋅001) and follicular fluid (P < 0⋅01) and LDL-cholesterol in plasma (P < 0⋅01). Progesterone released by luteal tissue into the culture medium in vitro from ewes given protected lipid was higher than that from tissue of control ewes (P < 0⋅05) and supplementary LH in vitro stimulated progesterone secretion by luteal tissues from both groups (P < 0⋅05). In conclusion, a dietary supplement of calcium soaps of fatty acids altered the intra-follicular environment surrounding the oocyte and follicular cells and enhanced luteal function in sheep.

Size distribution of bovine steroidogenic luteal cells during pregnancy

This study was designed to investigate the size distribution of bovine steroidogenic luteal cells throughout pregnancy. Corpora lutea collected from three different stages of pregnancy were used. Luteal tissue was dissociated into single-cell suspension by enzyme treatments. Cells were stained for 3β-hydroxysteroid dehydrogenase (HSD) activity a marker for steroidogenic cells. The steroidogenic cells covered a wide spectrum of size ranging from 10 to 60 µm in diameter. There was a significant increase in mean cell diameter (P > 0·05) as pregnancy progressed. Mean diameter of 3β-HSD positive cells increased from 17·03 (s.e. 1·3) µm in the corpus luteum of early pregnancy to 33·38 (s.e. 2·4) µm in the corpus luteum of advanced pregnancy. The ratio of large (>22 µm in diameter) to small (10 to 22 µm in diameter) luteal cells was 0·32 : 1·0 in the early pregnancy, with the 10 to 22 µm cell size class predominant. However, the ratio of large to small luteal cells was increased to 6·49 : 1·0 µm as pregnancy advanced and 23 to 42 µm cell sizes become predominant. It is likely that small luteal cells develop into large cells as gestation progresses. Development of pregnancy is associated with an increase in size of steroidogenic luteal cells.

Evidence of a molecular clock in the ovine ovary and the influence of photoperiod

The influence of the central circadian clock on reproductive timing is well established. Much less is known about the role of peripheral oscillators such as those in the ovary. We investigated the influence of photoperiod and timing of the LH surge on expression of circadian clock genes and genes involved in steroidogenesis in ovine ovarian stroma. Seventy-two Suffolk cross ewes were divided into two groups, and their estrous cycles were synchronized. Progestagen sponge removal was staggered by 12 hours between the groups such that expected LH peak would occur midway through either the light or dark phase of the photoperiodic cycle. Four animals from each group were killed, and their ovaries were harvested beginning 36 hours after sponge removal, at 6-hour intervals for 48 hours. Blood was sampled every 3 hours for the period 24 to 48 hours after sponge removal to detect the LH surge. The interval to peak LH did not differ between the groups (36.2 ± 1.2 and 35.6 ± 1.1 hours, respectively). There was an interaction between group and the time of sponge removal on the expression of the core clock genes ARNTL, PER1, CRY1, CLOCK, and DBP (P < 0.01, P < 0.05, P < 0.01, P < 0.01, and P < 0.01, respectively). As no significant interaction between group and time of day was detected, the datasets were combined. Statistically significant rhythmic oscillation was observed for ARNTL, CLOCK, CRY1 (P < 0.01, respectively), PTGS2, DBP, PTGER2, and CYP17A1 (P < 0.05, respectively), confirming the existence of a time-sensitive functionality within the ovary, which may influence steroidogenesis and is independent of the ovulatory cycle.

Effect of the stage of estrous cycle on follicular population, oocyte yield and quality, and biochemical composition of serum and follicular fluid in Anatolian water buffalo

This study was designed to investigate the effects that the different stages of the estrous cycle had on the number of surface ovarian follicles and oocyte yield and quality of Anatolian water buffalo during peak breeding season. Assessments were made on the basis of ovarian morphology, serum and follicular fluid concentrations of variety of biochemical parameters. Following slaughter, blood samples were collected from each animal. The stage of estrous cycle was classified as either the luteal or follicular phase, and surface ovarian follicles were classified as small, medium, or large. The follicular fluid was aspirated, and oocytes were evaluated microscopically for classification into four categories. No statistical differences (p>0.05) were observed regarding the total number of follicles or quality of oocytes relative to the stage of the estrous cycle. Serum high-density lipoprotein cholesterol (HDL), alkaline phosphatase (ALP) and progesterone (P4) concentrations were significantly higher in the luteal phase than in the follicular phase (P<0.05). Significant correlations were observed in the luteal phase between the total number of oocytes and cholesterol (Cho), HDL, sodium (Na), chloride (Cl); A-quality oocytes and Na, Cl, Mg; C-quality oocytes and Cho, HDL, and Mg in follicular fluid. These results offer new information concerning Anatolian water buffalo reproductive physiology, which may be useful for improving oocyte quality in buffalo. This is the first study to describe the number of ovarian follicles, oocyte yield and quality, and a variety of biochemical parameters in the serum and follicular fluid of Anatolian water buffalo during peak breeding season in Turkey.

Effects of omega-3 and -6 polyunsaturated fatty acids on ovine follicular cell steroidogenesis, embryo development and molecular markers of fatty acid metabolism

We previously reported increased follicular fluid progesterone (P(4)) concentrations in ewes fed an n-3 compared to an n-6 polyunsaturated fatty acid (PUFA)-enriched diet, but detected no differential effect of n-3 and n-6 PUFA-enriched high-density lipoproteins (HDL) on granulosa cell (GC) steroidogenesis in vitro. Moreover, net n-6 PUFA-enriched HDL reduced early embryo development, but in the absence of a net uptake of FA. Consequently, we hypothesised that a) effects of n-3 PUFA on ovarian steroidogenesis are mediated by theca rather than GCs and b) during embryo culture lipids are acquired solely from the albumin fraction of serum, so that albumin-delivered n-3 and n-6 PUFA exert a greater differential effect on embryo development than either low-density lipoprotein (LDL)- or HDL-delivered PUFA. Data confirmed that n-3 PUFA increases P(4) production solely in theca cells and that this is associated with an increase in STAR transcript expression. Furthermore, LDL- and HDL-delivered n-3 PUFA are equally efficacious in this regard during the first 96 h of culture, but thereafter only HDL-delivered n-3 PUFA induces this effect in partially luteinised theca cells. We also demonstrate that albumin is the sole serum fraction that leads to a net uptake of FA during embryo culture. PUFA-enriched serum and albumin increased the yield of morphologically poorer quality blastocysts with increased transcript expression for the antioxidant enzyme SOD1. Important differential effects of n-3 and n-6 PUFA on ovarian steroidogenesis acting solely on theca cells are identified, but differential effects of PUFA on embryo development are less apparent.

Oocyte quality in lactating dairy cows fed on high levels of n-3 and n-6 fatty acids

Different fatty acid (FA) sources are known to influence reproductive hormones in cattle, yet there is little information on how dietary FAs affect oocyte quality. Effects of three dietary sources of FAs (supplying predominantly palmitic and oleic, linoleic (n-6) or linolenic (n-3) acids) on developmental potential of oocytes were studied in lactating dairy cows. A total of 12 Holstein cows received three diets containing rumen inert fat (RIF), soyabean or linseed as the main FA source for three periods of 25 days in a Latin-square design. Within each period, oocytes were collected in four ovum pick-up sessions at 3-4 day intervals. FA profiles in plasma and milk reflected profiles of dietary FA sources, but major FAs in granulosa cells were not affected. Dietary FA source did not affect plasma concentrations of leptin, insulin, IGF1, GH, or amino acids. RIF led to a higher proportion of cleaved embryos than soya or linseed, but blastocyst yield and embryo quality were not affected. It is concluded that the ovary buffers oocytes against the effects of fluctuations in plasma n-3 and n-6 FAs, resulting in only modest effects on their developmental potential.

Intestinal hormones and growth factors: effects on the small intestine

There are various hormones and growth factors which may modify the intestinal absorption of nutrients, and which might thereby be useful in a therapeutic setting, such as in persons with short bowel syndrome. In part I, we focus first on insulin-like growth factors, epidermal and transferring growth factors, thyroid hormones and glucocorticosteroids. Part II will detail the effects of glucagon-like peptide (GLP)-2 on intestinal absorption and adaptation, and the potential for an additive effect of GLP2 plus steroids.

Effect of a calcium soap of fatty acids on reproductive characteristics and lactation performance of fat-tailed sheep

Experiments were carried out to study the effect of feeding Megalac, calcium soaps of fatty acids (protected fat), on reproduction and lactation of sheep. In the first experiment, 20 Ghezel and 20 Mehraban cyclic fertile ewes (4-5 years old) were randomly allotted to 4 groups. The control group was fed with a balanced ration and the other groups received the same diet as well as a daily allowance of 40 g non-protected fat (NP), 40 g protected fat (LP), or 80 g (HP) protected fat. The ewes were fed with their respective rations for one cycle length. Blood samples were collected and analyzed for progesterone (P4), cholesterol (CHOL), High Density Lipoproteins (HDL), Low Density Lipoproteins (LDL) and triacylglycerols (TG). The ewes were slaughtered on their next estrous period and the size and number of follicles in ovaries were recorded. There were no significant effects of feeding fat on ovarian weights, cycle length and follicular numbers in each class, or on the size of the largest follicle. Serum concentrations of P4, CHOL, TG and HDL were greater for HP ewes as compared with the control ewes (p<0.05). In the second experiment, effects on lactation and lamb performance of feeding protected fat during mating, late gestation and early lactation were studied in Mehraban ewes. Milk and fat yields on day 25 of lactation were significantly increased by feeding protected fat. Protected fat resulted in lower weight loss in ewes and a higher lamb birth weight. Average daily weight gain of lambs from birth to day 60 and the weaning weight of lambs were increased by feeding protected fat (p<0.05). In conclusion, calcium soaps of fatty acids increased serum P4 between days 10 to 14 of the cycle which may be beneficial to early pregnancy maintenance. Protected fat seemed to have a beneficial effect on milk yield, fat yield, lamb daily gain, lamb birth weight and ewe weight loss.

Roles for prostaglandins in the steroidogenic response of human granulosa cells to high-density lipoproteins

In human granulosa-lutein cells, high-density lipoproteins (HDL) can stimulate progesterone synthesis. The objective of the present study was to establish whether prostaglandins (PGs) participate in the steroidogenic response to HDL. Both HDL and apolipoprotein AI (ApoAI) stimulated concentration-dependent increases in PGE2, cAMP and progesterone accumulation. The minimum concentrations of HDL and ApoAI required to elevate PGE2 production were the same as those required to stimulate cAMP accumulation and progesterone synthesis. Concentrations of PGE2 were elevated within 10 min in cells exposed to HDL and rose progressively over 24 h, whereas cAMP and progesterone were only increased significantly after 24 h of treatment with HDL. Co-treatment with prostaglandin H synthase inhibitors (meclofenamic acid and indomethacin) abolished the cAMP and progesterone responses to both HDL and ApoAI. Hence, the ability of HDL to stimulate progesterone synthesis can be mimicked by ApoAI and appears to involve increased generation of one or more luteotrophic PGs, possibly acting via cAMP.

9-cis-retinoic acid during in vitro maturation improves development of the bovine oocyte and increases midkine but not IGF-I expression in cumulus-granulosa cells

The isomer 9-cis of retinoic acid (9-cis-RA) exerts a beneficial effect on bovine in vitro development when added to in vitro maturation (IVM) culture. In the present work, 9-cis-RA 5 nM was found to be stimulatory as opposed to 500 nM (toxic). Cumulus-oocyte complexes (COCs) were treated with the found physiological dose 9-cis-RA 5 nM, and the next determinations performed: (1) relative expression of midkine (MK) and IGF-I, by reverse transcriptase-polymerase chain reaction (RT-PCR), in cumulus-granulosa cells detached from oocytes; (2) cytoplasmic granular migration, by labeling of oocytes with fluoroscein isothiocyanate lectins; and (3) in vitro survival of blastocysts after vitrification and warming. Gene expression of MK was enhanced by 9-cis-RA, but not by 1% ethanol (vehicle). However, we did not detect IGF-I expression, both in dependence on or in the absence of 9-cis-RA acting on cumulus-granulosa cells. The ability of vitrified blastocysts to survive in vitro was not improved by 9-cis-RA. Nevertheless, since only blastocysts obtained from oocytes matured with serum survived, more factors should be considered when evaluating cryopreservation survival. The complete granular migration observed in oocytes matured with 9-cis-RA anticipates the gain in developmental competence of the oocyte, being MK probably involved in this beneficial effect.

Ovarian stanniocalcin is structurally unique in mammals and its production and release are regulated through the luteinizing hormone receptor

Stanniocalcin (STC) is a recently discovered mammalian hormone that is widely distributed in many tissues. In rodents the STC gene is most highly expressed in ovary, specifically in androgen-producing thecal and interstitial cells. In addition, ovarian levels of expression rise 15-fold over pregnancy. The objective of this study was to develop a primary culture system for ovarian thecal-interstitial cells (TICs) to identify factors governing STC production and release. We used highly purified primary cultures of rat and bovine TICs, the purity of which was routinely assessed with antigenic and enzymatic markers. The functionality of cells was assured by their responsiveness to LH in the form of progesterone release. We found that forskolin significantly increased STC gene expression and secretion by both rat and bovine TICs, an effect that was only replicated by human (h) chorionic gonadotropin (CG). Coincubation of TICs with hCG and phosphodiesterase inhibitors further increased STC secretion, whereas coincubation of TICs with hCG and protein kinase A inhibitors attenuated hCG-stimulated release. Intriguingly, ovarian STC proved to be substantially larger than the 50-kDa homodimer produced in most other tissues. These results indicate that ovarian STC is physically distinct, a feature that could explain its presence in serum during pregnancy and lactation.

Scavenger receptor class BI and selective cholesteryl ester uptake: partners in the regulation of steroidogenesis

The steroidogenic tissues have a special requirement for cholesterol, which is used as a substrate for steroid hormone biosynthesis. In many species this cholesterol is obtained from plasma lipoproteins by a unique pathway in which circulating lipoproteins bind to the surface of the steroidogenic cells and contribute their cholesteryl esters to the cells by a 'selective' process in which the whole lipoprotein particle does not enter the cell. This review describes the lipoprotein selective cholesteryl ester uptake process and its specific partnership with the HDL receptor, scavenger receptor class BI (SR-BI). It describes the characteristics of the selective pathway, and the molecular properties, localization, regulation, anchoring sites and potential mechanisms of action of SR-BI in facilitating cholesteryl ester uptake by steroidogenic cells.

Raman spectroscopy and imaging of beta-carotene in live corpus luteum cells

Raman spectroscopy has been used to identify and locate beta-carotene within individual living luteal cells. The cells were either freshly prepared or cultured; the latter was incubated in the presence or absence of beta-carotene in the form of enriched bovine high-density lipoprotein. Luteal cells were investigated using several Raman spectroscopic and imaging techniques. These techniques did not give accurate concentration levels of beta-carotene within parts of the cell but illustrated the distribution of the molecule. Freshly prepared luteal cells were found to contain an appreciable concentration of beta-carotene. Over a period of several days, the concentration gradually reduced to a nearly undetectable level; similar results were found for cells cultured in the absence of the beta-carotene. For cells cultured in the presence of beta-carotene, the molecular concentration was maintained for as long as 2 weeks. The Raman spectra of fragmented cells showed that the beta-carotene is predominantly localised in the lipid-rich cell components, with the concentration highest in the microsomal fraction. The Raman imaging techniques revealed that beta-carotene was spread over the entire volume of the luteal cells with higher levels occurring at distinct sites, including the surface.

Development and validation of a short-term, serum-free culture system for bovine granulosa cells: evaluation of the effects of somatotropin and growth hormone-releasing factor on estradiol production

The objective of this study was to develop and validate a short-term, serum-free culture system to determine whether recombinant bovine somatotropin (rbST) or recombinant bovine growth hormone-releasing factor (rbGRF) altered the estradiol-producing capacity of bovine granulosa cells isolated from dominant or subordinate follicles of the first follicular wave. Thus, ovaries were obtained at an abattoir from cows that were between d 2 to 5 or 6 to 10 of the estrous cycle. Three size classes of follicles were isolated from each cow's ovaries: small (2 to 5 mm in diameter), medium (6 to 14 mm), or the largest (6 to 19 mm). In vivo steroid-producing capacity of follicles was assessed by measuring concentration of estradiol, progesterone, androstenedione and 5alpha-dihydrotestosterone in each follicle. In vitro steroid-producing capacity was assessed by culturing granulosa cells from the different follicle sizes for 48 h in serum-free media with 19-OH androstenedione and measuring the estradiol and progesterone concentrations in media at the end of culture. The effect of different doses of FSH, rbST, or rbGRF on estradiol and progesterone production by granulosa cells from each follicle size class during d 2 to 5 or 6 to 10 was also evaluated. A high percentage (91.7%) of the largest follicles obtained on d 2 to 5 was estrogen-active (estradiol > progesterone) compared with other follicle classifications (d 2 to 5, small = 0%, medium = 13.8%; d 6 to 10, small = 0%, medium = 3.3%, largest = 33.3%). Estradiol was highest (P < 0.05) in the largest follicle on d 2 to 5 and correlated positively with follicle diameter. The pattern of in vitro production of estradiol by granulosa cells from the different follicle size classes reflected the original in vivo capacity of follicles to produce estradiol. However, only granulosa cells from the largest estrogen-active follicle on d 2 to 5 produced more estradiol than progesterone in vitro. Progesterone production by granulosa cells from all follicle classifications was increased by FSH, but FSH only enhanced estradiol production by granulosa cells from the largest estrogen-active follicles on d 2 to 5. Recombinant bST blocked the FSH-induced increase in estradiol by granulosa cells from the largest estrogen-active follicles on d 2 to 5, whereas rbGRF had no effect on steroid production. Based on these results, we concluded that short-term, serum-free culture of bovine granulosal cells obtained from first-wave follicles at an abattoir could be used to reflect reliably the original in vivo estradiol-producing capacity of granulosal cells, and that neither rbST nor rbGRF enhance basal or FSH-induced estradiol production by bovine granulosa cells from first-wave follicles.

Effect of cyclodextrin-encapsulated beta-carotene on progesterone production by bovine luteal cells

Experiments were conducted to examine the effect of cyclodextrin-encapsulated beta-carotene on basal or cholesterol (cyclodextrin-encapsulated), LH and dibutyryl cyclic AMP (dbcAMP)-stimulated progesterone production by bovine corpus luteum cells isolated from mid-luteal heifer ovaries by collagenase digestion. Cells were cultured with serum-free DMEM/Ham's F12 medium in serum pre-treated plastic culture dishes for periods of up to 11 days. Medium was replaced after 24h and thereafter every 48 h. Beta-carotene was added to cultures in a carrier molecule, dimethyl-beta-cyclodextrin, to facilitate dissolution. All treatments were started on day 3 of culture. Treatment of cells with 1 or 2 micromol/l beta-carotene resulted in sharp inhibition of progesterone production. On the contrary, treatment of cells with 0.1 micromol/l beta-carotene resulted in significant stimulation (P<0.05) of both basal and cholesterol-stimulated progesterone secretion. The effect of beta-carotene on LH or dbcAMP-stimulated progesterone production was also examined. Treatment of cells with LH or dbcAMP always resulted in stimulation of progesterone secretion (P<0.001). However, cells treated with LH plus beta-carotene or dbcAMP plus beta-carotene both produced significantly (P<0.01) less progesterone relative to those cells treated with LH or dbcAMP alone on days 7, 9 and 11 of culture. These results indicate that beta-carotene can enhance luteal steroidogenesis when present at low concentrations but is inhibitory at higher concentrations and that encapsulation of beta-carotene in cyclodextrin is an effective method of supplying it to cells in culture.

Effects of high density lipoprotein containing high or low beta-carotene concentrations on progesterone production and beta-carotene uptake and depletion by bovine luteal cells

Luteal cells were isolated from mid-luteal heifer ovaries by collagenase digestion. Cells were cultured with DMEM/Ham's F12 medium in serum pre-treated plastic culture dishes for periods of up to 11 days. As beta-carotene is almost completely insoluble in all polar solvents, it was added to cultures in either dimethyl sulphoxide (DMSO), tetrahydrofuran (THF) or as high-density lipoprotein (HDL) containing high or low beta-carotene concentrations. Medium was replaced after 24 h, thereafter medium was changed every 48 h. Treatment of cells with DMSO alone or with beta-carotene (5 micromol/l) in DMSO both resulted in significant (P<0.01) stimulation of progesterone production. beta-Carotene (5 micromol/l) in THF did not alter progesterone production but 50 micromol/l beta-carotene in THF resulted in significant inhibition (P<0.02) of progesterone production on days 3 and 7. Cultures were also supplemented with bovine HDL preparations containing equal concentrations of cholesterol (25 microg/ml) but high or low beta-carotene (12.4 or 0.44 microg/mg of cholesterol). Both HDL preparations significantly stimulated progesterone production (P<0. 001) but the high beta-carotene HDL was significantly (P<0.02) more effective than the low beta-carotene HDL. However, when given together with bovine luteinizing hormone (bLH) or dibutyryl cAMP (dbcAMP), the high beta-carotene HDL stimulated progesterone production less than did the low HDL (P<0.01). Uptake and depletion of beta-carotene by luteal cells were also examined in culture. beta-Carotene supplementation increased luteal cell beta-carotene from an initial level of 373 ng per 10(6) cells to 2030 ng per 10(6) cells by day 6. In contrast, the levels in control cells decreased to 14% of starting values during the same period. Cells treated with HDL containing high beta-carotene on day 1 or days 1 and 3 were then incubated with or without bLH or dbcAMP for a further 2 days to investigate the effect of bLH and dbcAMP on depletion of beta-carotene by luteal cells. beta-Carotene depletion in the luteal cells was significantly higher (P<0.05) in LH- and dbcAMP-treated cells than in the control cells in both groups. These results indicate that the use of solvents such as DMSO or THF may have undesirable effects due to alteration of cell membrane permeability. Supplementation with bLH or dbcAMP may increase the metabolism of beta-carotene in luteal cells. bLH or dbcAMP together with high beta-carotene HDL may, when combined with the effect of increased beta-carotene metabolism, give less stimulation than with low beta-carotene HDL.

Tumor necrosis factor-alpha stimulates proliferation of rat ovarian theca-interstitial cells

Tumor necrosis factor-alpha (TNF-alpha) is a potent modulator of ovarian function, affecting steroidogenesis of both granulosa and theca-interstitial (T-I) cells. Women with polycystic ovary syndrome (PCOS) have increased levels of serum TNF-alpha. The present study evaluated the effects of TNF-alpha on T-I cell proliferation. Purified rat T-I cells were cultured for 48 h with or without TNF-alpha (0.001-1 nM), insulin-like growth factor I (IGF-I; 10 nM), and/or insulin (10 nM). Proliferation was measured by [(3)H]thymidine incorporation assay and by counting the steroidogenically active (stained positive for 3beta-hydroxysteroid dehydrogenase; 3beta-HSD) and inactive (3beta-HSD negative) cells. TNF-alpha stimulated thymidine incorporation in a dose-dependent fashion (up to 3.2-fold; P < 0.01). Insulin and IGF-I stimulated T-I proliferation (respectively, by up to 2.4- and 3.1-fold; P < 0.001). TNF-alpha potentiated effects of insulin and IGF-I in a dose-dependent and additive fashion (up to 6.7-fold; P < 0.001). TNF-alpha (1 nM) increased total cell count (by 80%, P < 0.05) and the proportion of 3beta-HSD-positive cells (by 19%, P < 0.05). Flow cytometry DNA analysis revealed that TNF-alpha (1 nM) increased the proliferative index by up to 16% (P = 0.05). The present findings demonstrate that TNF-alpha stimulates mitotic activity of T-I cells by increasing the proportion of actively dividing cells and preferentially increasing the number of steroidogenically active cells. The effects of TNF-alpha appear to be independent of those induced by insulin and IGF-I. We postulate that TNF-alpha may play a pathophysiologic role in disorders of the T-I compartment, such as PCOS.

Proliferation and differentiation of rat theca-interstitial cells: comparison of effects induced by platelet-derived growth factor and insulin-like growth factor-I

This study was designed to evaluate mechanisms regulating proliferation of steroidogenically active and steroidogenically inactive theca-interstitial (T-I) cells, and, specifically, to evaluate the effects of platelet-derived growth factor (PDGF) and insulin-like growth factor-I (IGF-I). T-I cells obtained from immature Sprague-Dawley rats were cultured in chemically defined media. Proliferation was assayed by thymidine incorporation and cell counting. Steroidogenically active cells were identified by the presence of 3beta-hydroxysteroid dehydrogenase activity. Flow cytometry facilitated separation of dividing cells (in S and G2/M phases of the cell cycle) from nondividing cells (in G0 and G1 phases of the cell cycle). PDGF alone (0.1-1 nM) produced a dose-dependent increase in DNA synthesis by up to 136%. IGF-I alone (10 nM) increased DNA synthesis by 56%. In the presence of both IGF-I (10 nM) and PDGF (0.1-1 nM), DNA synthesis increased by 108-214%. PDGF (1 nM) increased the total number of T-I cells by 43%; this effect was due to an increase in the number of steroidogenically inactive cells (47%). In contrast, the stimulatory effect of IGF-I (10 nM) was predominantly due to an increase in the number of steroidogenically active cells (163%). Separation of dividing cells from nondividing cells was accomplished with the aid of flow cytometry. In the absence of growth factors, the proportion of steroidogenically active cells was 35% lower among proliferating than resting cells. PDGF (1 nM) decreased the proportion of steroidogenically active cells among both proliferating and resting cells (by 43% and 16%, respectively). In contrast, IGF-I (10 nM) increased the proportion of steroidogenically active cells among proliferating cells by 56%. These findings indicate that differentiated/steroidogenically active cells divide; furthermore, PDGF and IGF-I may selectively stimulate proliferation of individual subpopulations of T-I cells, thereby providing a mechanism for development of structural and steroidogenically active components of the T-I compartment.

Androstenedione and progesterone production in vitro by the inner or the outer theca cells in preovulatory follicles of gonadotropin stimulated calves

This study reports some of the steroidogenic characteristics of the interna and externa theca cells taken from young and eCG primed calves. These cells were isolated from large healthy follicles. The were separately cultured for 3 days in absence or in presence of steroid substrates. Androstenedione (A4) and progesterone (P4) were measured by radioimmunoassay (RIA). In control conditions, A4 levels, higher in interna than in externa cells (P < 0.001), decreased during cultures (P < 0.01). In both cell types, A4 increased in presence of 17 alpha-hydroxypregnenolone (17OHP5), pregnenolone (P5) and 22R-hydroxycholesterol (22R-chol)(*P < 0.05) but not with P4 or 17 alpha-hydroxyprogesterone (17OHP4)(P > 0.05). The most efficient substrate was dehydroepiandrosterone (DHEA) (P < 0.005). In control conditions, P4 levels increased in both cell types. They were higher in externa than in interna cells on day 1, the reverse was observed on day 3. P4 levels increased after addition of 22 R-chol and P5 (P < 0.005) but not with 17OHP5, 17OHP4 and DHEA (P > 0.05) from day 1 in externa cells and only on day 3 in internal cells. P4 levels measured on day 1 were lower than the quantity of P4 added as a substrate. These results, obtained with theca cells from young calf follicles, indicate: 1/A4 is synthesized by the delta5 pathway and 17 alpha-hydroxylase activity decreases in vitro, 2/externa and interna cells differ by the quantities of A4 and P4 produced, 3/both lack precursors to produce A4 and P4 but their 3 beta-hydroxysteroid dehydrogenase activity subsists, 4/P4 could be metabolized during the first 2 days in both cell cultures.

Sequence of the bovine HDL-receptor (SR-BI) cDNA and changes in receptor mRNA expression during granulosa cell luteinization in vivo and in vitro

Steroidogenic activity in the mature corpus luteum of most mammals depends upon provision of cholesterol from the circulating lipoproteins. In cattle, as in many species, high-density lipoprotein (HDL) is the major lipoprotein involved. The recent identification of the scavenger receptor SR-BI as an HDL-receptor allows control of this process to be investigated more closely. In this study, we have sequenced the bovine SR-BI HDL-receptor and examined changes in expression of the receptor mRNA during corpus luteum development in vivo and granulosa cell luteinization in vitro. Sequencing of the bovine HDL-receptor showed that it codes for a protein of 509 amino acids with close identity to hamster, mouse, rat and human sequences. Examination of the tissue distribution of the HDL-receptor mRNA showed high levels in adrenal cortex and corpus luteum and lower levels in spleen and liver. Using a semi-quantitative, reverse transcription-polymerase chain reaction technique levels of HDL-receptor mRNA were measured in corpora lutea from cattle at known stages of the oestrus cycle and in bovine granulosa cells luteinized in culture. Levels of HDL-receptor mRNA were low in isolated bovine granulosa cells, but increased 7-fold during corpus luteum development in vivo and 5-fold during granulosa cell luteinization in culture. Results show that luteinization of granulosa cells is associated with an increase in HDL-receptor RNA levels which, along with changes in steroidogenic enzyme activity, is likely to explain the marked increase in steroidogenic capacity which occurs during corpus luteum formation.

Steroid productions by co-cultures of granulosa cells with inner and outer theca cells in preovulatory follicles of gonadotropin stimulated calves

Granulosa, interna and externa theca cells were isolated from large follicles of equine-chorionic-gonadotropin (eCG)-primed calves and co-cultured during 3 days in the absence or in the presence of dehydroepiandrosterone (DHEA). Co-cultures were performed by adding defined numbers of theca and/or granulosa cells which represented 0, 10, 20, 50 or 100% of total cells per well. Secretion of oestradiol-17beta (E2), androstenedione (A4) and progesterone (P4) depended on the type of theca cells (P < 0.001), on the percentage of seeded granulosa cells (P < 0.001) and on the day of culture (P < 0.001). DHEA increased (P < 0.001) E2 and A4, but not P4 (P > 0.05) productions. Interactions existed between these factors (P < 0.01). On day 1, A4 production was nil in granulosa cells alone. E2 production was negligible in theca cells alone but it increased when granulosa cells were added. E2 and A4 varied in an opposite manner according to the percentage of granulosa cells and with the type of theca cells. On day 3, without DHEA, E2 and A4 were low. On day 3 with DHEA, E2 production was maintained in granulosa cells alone but not with any combination of theca cells. In these conditions, A4 production was maintained in the presence of theca cells but not in granulosa cells alone. Granulosa cells alone secreted more P4 than theca cells. P4 increased as a function of the percentage of granulosa in co-cultures with externa but not interna theca cells with which it remained low. In conclusion, theca cells in culture have two effects in relation to the granulosa cells, which differ according to the steroid concerned and to the cell combination. Both types of theca cells have an inhibitory effect on E2 secretion whereas only interna theca cells are able to alter P4 production.