Ovarian granulosa cell-derived insulin-like growth factor binding proteins: modulatory role of follicle-stimulating hormone

Rooibos (Aspalathus linearis) and its constituent quercetin can suppress ovarian cell functions and their response to FSH

Rooibos (Aspalathus linearis Brum. f) can directly influence female reproduction, but whether rooibos can influence the response of ovarian cells to FSH and whether the rooibos effects are due to the presence of quercetin remain unknown. We compared the influence of rooibos extract and quercetin (both at 10 µg/ml-1) on porcine ovarian granulosa cells cultured with and without FSH (0, 1, 10 or 100 ng/ml-1). The expression of intracellular proliferation (PCNA, cyclin B1) and apoptosis (bax, caspase 3) markers in the cells was detected by immunocytochemistry. The release of progesterone (P), testosterone (T) and estradiol (E) were evaluated with ELISAs. Administration of both rooibos and quercetin reduced the accumulation of proliferation markers and promoted the accumulation of apoptosis markers and the release of T and E. Rooibos stimulated, but quercetin inhibited, P output. Administration of FSH increased the accumulation of proliferation markers, decreased the accumulation of apoptosis markers, promoted the release of P and T, and had a biphasic effect on E output. The addition of both rooibos and quercetin mitigated or prevented the main effects of FSH. The present observations suggest a direct influence of both rooibos and quercetin on basic ovarian functions - proliferation, apoptosis, steroidogenesis and response to FSH. The similarity in the major effects of rooibos and its constituent quercetin indicates that quercetin could be the molecule responsible for the main rooibos effects on the ovary. The potential anti-reproductive effects of rooibos and rooibos constituent quercetin, should be taken into account in animal and human nutrition.

The Concept of Growth Hormone Deficiency Affecting Clinical Prognosis in IVF

The current understanding of human growth hormone (hGH; here GH) action is that the molecule is a 191-amino acid, single-chain polypeptide that is synthesized, stored and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland. It can be classified as a protein (comprising more than 50 amino acids) but true proteins have tertiary and quaternary chains creating a more complex structure, hence GH is usually classified as a polypeptide. GH is normally secreted at night during sleep and promotes skeletal, visceral and general body growth through the action of somatomedins or IGFs, notably IGF-1. In some tissues, GH action is directed via specific receptors GHRs; these are most abundant in liver, adipose and muscle tissues but have also been shown in granulosa cells, testicular tissues and on the oocyte, as well as in glandular cells of the luteal phase endometrium and decidua; such findings being recent and minimally researched to now. Following engagement with its receptor, the transduction process activates multiple signaling proteins. These all lead to extensive metabolic and mitogenic (growth promoting) responses. Clinically, GH is known to have an important role in pubertal development and is a key hormone for the vigor associated with adolescence and early adult life stages but has a faded presence and role for later adulthood, beyond age 30 years, and is minimally detected in advanced age, beyond 40 years. In association with the rapidly increasing trend for delaying reproduction beyond age 35 years, GH is being widely researched now as a potential adjuvant for infertility treatment in this group who, studies consistently show, have a poorer prognosis than younger females when relying on autologous oocytes. The idea that the age-related reduction in fertility prognosis is a feature of growth hormone deficiency is supported by our studies showing an elevated binding protein IGFBP-3/IGF-1 ratio and this can be reduced to a normal range (matching younger, good prognosis women) by the administration of GH as an adjuvant.

Frequency of luteinizing hormone pulses in cattle influences duration of persistence of dominant ovarian follicles, follicular fluid concentrations of steroids, and activity of insulin-like growth factor binding proteins

The objectives of the present study were to determine how varying frequency of LH pulses as controlled by varying treatments with progesterone (P4) in cattle would affect: (1) concentration of steroid hormones and activity of insulin-like growth factor binding proteins (IGFBPs) in the ovarian follicular fluid and blood plasma, and (2) duration of persistence of largest ovarian follicles. There were four treatment groups (n=7 per group) and a control group (n=5) of mature, non-lactating beef cows. Treatments were: (1) two progesterone releasing intravaginal devices (PRIDs) for 16 days (2PRID); (2) a half PRID for 16 days (0.5PRID); (3) two PRIDs for 8 days, then a half PRID for 8 days (2-0.5PRID); or (4) a half PRID for 8 days, then two PRIDs for 8 days (0.5-2PRID). Treatment was initiated on the fifth day of the estrous cycle, which was designated as Day 0, and continued for 16 days. All P4-treated females were administered prostaglandin F2alpha on Day 0 and 1 to regress their corpora lutea. Frequency of LH pulses was greater during treatment with the smaller dose of P4 compared with treatment with the larger dose of P4 and the control group. Ovarian follicles were classified into five categories based on ultrasonographic observations: growing (G); atretic (A); growing dominant (GD); growing persistent (GP); or atretic persistent (AP). At ovariectomy on Day 16, the largest and second largest follicles collected were re-classified into five categories based on follicular concentration of steroids. Classification of the largest follicle collected on Day 16 was influenced by treatment (P<0.005), with the 2PRID group having A follicles, the 2-0.5PRID group GP follicles, the 0.5-2PRID group AP follicles, and the 0.5PRID group GD and GP follicles. Concentrations of 17beta-estradiol (E2) were greatest in GD and GP follicles (P<0.05). There was less (P<0.05) activity of IGFBP-2 in GD follicles and less (P<0.05) activity of IGFBP-3 in GD and GP follicles than other follicles. Activity of IGFBP-4 and -5 was greater (P<0.05) in A and AP follicles than G, GD, and GP follicles. Maintenance of a frequent release of LH pulses over a 16-day period did not result in maintenance of persistent follicles throughout this period indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia is associated with greater activity of IGFBP-2, -4, -5, and greater concentrations of P4 in follicles, whereas growing dominant and persistent follicles contained greater concentrations of E2, androstenedione (A4), and less IGFBP-2 activity than follicles of other classes. Follicle classifications based on ultrasonography or follicular concentration of steroids did differ (P<0.05) for the largest follicles from the 2PRID group. Two follicles in this group appeared as GD follicles by ultrasonography, but these were atretic based on follicular steroid contents. Objective 1 of the present study yielded the conclusion that concentrations of steroid hormones in follicular fluid and blood plasma could be predictably controlled by regulating the frequency of LH pulses with varying doses of P4. Objective 2 yielded the conclusion that maintain frequent release of LH pulses over a 16-day period could not maintain persistent follicles throughout this period, indicating that duration of dominance of these follicles is finite even when there is frequent release of LH pulses. Follicular atresia in the present study was associated with increased follicular fluid activity of IGFBP-2, -4, -5, and P4, whereas growing dominant and persistent follicles contained greater concentrations of E2, A4, and less IGFBP-2 activity than follicles of other classes.

Regulation of granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs): role for protein kinase-C in the pre- and posttranslational modulation of IGFBP-4 and IGFBP-5

A growing body of information suggests antigonadotropic and atretogenic roles for granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs) 4 and 5 during ovarian folliculogenesis. Activation of protein kinase-A (PKA) in rat granulosa cells has been shown to modulate the relative expression of IGFBP-4 and -5 transcripts and proteins. In this article, we assess the role of protein kinase-C (PKC) in this regard. Provision of granulosa cells with phorbol 12-myristate 13-acetate (PMA) (but not 4alphaPMA, an inert analogue), a tumor-promoting phorbol ester and an established activator of PKC, was without significant effect on the expression of IGFBP-4 transcripts but resulted in biphasic dose-dependent alterations in IGFBP-5 transcripts and in the accumulation of the IGFBP-4 and -5 proteins. Comparable effects were noted for GnRH, an established PKC agonist. Provision of staurosporine, a potent inhibitor of the catalytic subunit of PKC, produced significant dose-dependent decrements in the relative expression of IGFBP-5 transcripts. Treatment with FSH (presumptively PKA-mediated) markedly attenuated the ability of PMA or GnRH to upregulate the accumulation of the IGFBP-5 (but not IGFBP-4) protein. Taken together, our present findings indicate that the modulation of rat ovarian IGFBP-4 and -5 is PKC as well as PKA dependent and that these two signaling pathways interact in a diametrically opposed and antagonistic fashion.

The final stages of dominant follicle selection in cattle

The final stages of ovarian follicle growth in cattle are typically characterized by the ultrasound-detectable emergence of a cohort of small (3-5mm in diameter) antral follicles, followed by a selection process during which the number of follicles continuing to grow decreases. Finally, only one follicle (the dominant follicle; DF) shows an enhanced growth rate and estradiol synthesis when it attains 8.5mm compared to its closest competitor (the largest subordinate follicle; SF). Cohort emergence is caused by a transient FSH rise, while DF selection occurs during declining FSH indicating differential FSH dependence of DF and SF. In order to elucidate the mechanisms underlying DF survival or SF atresia, this review aims to (i) describe follicular changes in the local production and regulation of members of the inhibin family of proteins and the insulin-like growth factor (IGF) system in relation to FSH deprivation leading to DF selection, and (ii) develop a model for DF selection outlining the putative involvement of inhibins, activin and follistatin on the one hand, and bioavailable IGFs regulated by IGF binding proteins (IGFBPs) and IGFBP proteases on the other hand. It is concluded, that the first indications of differential FSH dependence are seen within 33h of the FSH peak, and high amounts of precursor forms of inhibin and free activin, and low amounts of the lower molecular weight (MW) IGFBPs are related to follicle survival in terms of enhanced growth and estradiol synthesis, and suppression of granulosa cell apoptosis. In addition, maintenance of low amounts of intrafollicular IGFBP4 may constitute an important mechanism in the future DF to attain FSH independence.

Alterations in intrafollicular regulatory factors and apoptosis during selection of follicles in the first follicular wave of the bovine estrous cycle

Changes in follicular fluid (FF) concentrations of estradiol, inhibin forms, and insulin-like growth factor binding proteins (IGFBPs), percentage of apoptotic granulosa cells (%A), and follicular size for individual follicles in a growing cohort were determined throughout the first wave of follicular development during the bovine estrous cycle and related to FSH decline. Four groups of heifers (n = 31) were ovariectomized between Days 1.5 and 4.5 of the estrous cycle at 5 +/- 1, 33 +/- 2, 53 +/- 1, and 84 +/- 2 h after the periovulatory peak in FSH concentrations. Follicles > or = 2.5 mm were dissected, measured, and FF aspirated. The five largest follicles were ranked based on their diameter (F1 to F5). Diameters of F1 to F5 were positively correlated with interval from FSH peak (r > or = 0.6, P < 0.05). Five hours after the FSH peak, follicular diameter and FF concentrations of estradiol, inhibins, and IGFBPs were similar for F1 to F5. From 5 to 33 h, amounts of the six precursor inhibin forms (> or = 48 kDa) increased (P < 0.05) in F1 follicles. The IGFBPs in F1 follicles remained low at all time periods. At 33 h, amounts of IGFBP-4 and -5 were higher (P < 0.05) in F4 and F5 compared with F1 follicles. At 84 h, IGFBP-2, -4, and -5 were increased (P < 0.05) in F3, F4, and F5 compared with F1. At 5, 33, or 53 h, %A was not different between follicles in any size class. At 84 h %A was increased (P < 0.05) in follicles <6 mm in diameter. However, at that time, %A did not differ between the selected DF and the largest subordinate follicle. For individual heifers, the selected DF at 84 h was largest in size, highest in estradiol, and lowest in IGFBP-2 and -4. The F1 follicle had highest estradiol in 23 of 27 heifers irrespective of stage of the wave and lowest IGFBP-4 in 19 of 21 heifers from 33 h. We concluded that the earliest intrafollicular changes that differentiate a dominant-like follicle from the growing cohort are enhanced capacity to produce estradiol and maintenance of low levels of IGFBPs.

Effect of cell-to-cell contact on in vitro deoxyribonucleic acid synthesis and apoptosis responses of bovine granulosa cells to insulin-like growth factor-I and epidermal growth factor

Follicle development is the result of a balanced ratio between cell proliferation and cell death. Previous studies demonstrated differential mitotic responses to insulin-like growth factor (IGF)-I and epidermal growth factor (EGF) of cumulus cells (CC) and mural granulosa cells (MGC). Because cell-to-cell contact seems to modulate the occurrence of programmed cell death, the present experiments investigated the role of cell association in mediating apoptosis and the mitogenic responses to these growth factors of CC and MGC. Cumulus cells were cultured either as intact cumulus-oocyte complexes (COC) or after dissociation with EGTA + sucrose, in the presence of 50 ng/ml IGF-I, 5 ng/ml EGF, or both. Mural granulosa cells from the same follicles were similarly cultured either as cell aggregates or as dissociated cells. Synthesis of DNA was assessed by measurement of [(3)H]thymidine incorporation during the last 6 h of a 24-h culture in TCM199. Percentages of cells undergoing apoptosis were determined immunohistochemically in intact COC and GC aggregates, before and after dissociation as well as after the culture period. Epidermal growth factor and IGF-I stimulated DNA synthesis in both cell types; however, EGF inhibited the action of IGF-I in intact COC but not in MGC. Compared to nondissociated cells, dissociation resulted in a reduction of the mitogenic response of CC to both growth factors and of MGC to EGF. Unlike the response of intact COC to combined treatment with the two growth factors, dissociated CC displayed additive responses to the two growth factors in combination. Addition of denuded oocytes to cultures of dissociated CC enhanced both basal and growth factor-stimulated DNA synthesis but did not restore the inhibitory effect of EGF on the IGF-I response characteristic of intact COC. A significant proportion of intact MGC aggregates underwent apoptosis after 24 h of culture, while no increase of apoptotic cells was observed in intact COC. A dramatic increase in the percentage of apoptotic cells was observed in both CC and MGC when cell-cell contact was interrupted, and EGF and IGF-I were able to partially prevent its occurrence. Taken together these data showed that CC and MGC exhibit qualitatively and quantitatively different responses to IGF-I when cultured in the presence of EGF both in terms of DNA synthesis and onset of apoptosis. Moreover, the disruption of cell-cell contact was a major factor reducing cell proliferation and inducing apoptosis among both subsets of GC.

Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid activity in the female rat. A focus on the EDSTAC recommendations

In 1996, the US Environmental Protection Agency was given a mandate by Congress to develop a screening program that would evaluate whether variously identified compounds could affect human health by mimicking or interfering with normal endocrine regulatory functions. Toward this end, the Agency chartered the Endocrine Disruptor Screening and Testing Advisory Committee in October of that year that would serve to recommend a series of in vitro and in vivo protocols designed to provide a comprehensive assessment of a chemical's potential endocrine-disrupting activity. A number of these protocols have undergone subsequent modification by EPA, and this review focuses specifically on the revised in vivo screening procedure recommended under the title Research Protocol for Assessment of Pubertal Development and Thyroid Function in Juvenile Female Rats. Background literature has been provided that summarizes what is currently known about pubertal development in the female rat and the influence of various forms of pharmaceutical and toxicological insult on this process and on thyroid activity. Finally, a section is included that discusses technical issues that should be considered if the specified pubertal endpoints are to be measured and successfully evaluated.

Transcriptional and posttranscriptional regulation of intraovarian insulin-like growth factor-binding proteins by interleukin-1beta (IL-1beta): evidence for IL-1beta as an antiatretic principal

Intraovarian interleukin-1 (IL-1), a putative intermediary in the ovulatory cascade, has recently been implicated as an antiatretic agent. Given the reported antigonadotropic and thus atretogenic potential of granulosa cell-derived insulin-like growth factor-binding proteins (IGFBPs), we evaluated the ability of IL-1beta to regulate ovarian IGFBP-4 and -5, the IGFBP species elaborated by the rat granulosa cell. Treatment of whole ovarian dispersates of immature rat origin with increasing concentrations of IL-1beta for 96 h resulted in substantial and significant time-dependent inhibition of IGFBP-4 and IGFBP-5 transcripts compared with that in untreated controls. The IL-1 effect proved relatively specific in that no significant alterations in IGFBP transcripts were observed in the presence of select ovarian agonists, including transforming growth factor-alpha, tumor necrosis factor-alpha, endothelin-1, hepatocyte growth factor, keratinocyte growth factor, or basic fibroblast growth factor. The inhibitory effect of IL-1beta on ovarian IGFBP-4 and -5 expression was almost completely reversed in the presence of IL-1 receptor antagonist, suggesting mediation via a specific IL-1 receptor. The addition of actinomycin D to IL-1beta-pretreated whole ovarian dispersates produced a pattern of (IGFBP-4 and -5) messenger RNA decay indistinguishable from that noted for the untreated control group. Medium conditioned by IL-1beta-treated (but not untreated) whole ovarian dispersates displayed a marked diminution in the relative content of the IGFBP-4 and IGFBP-5 proteins (24- and 28- to 29-kDa proteins, respectively). Medium conditioned by IL-1beta-treated (but not untreated) whole ovarian dispersates proteolyzed [125I]IGFBP-5 (but not IGFBP-4) into fragments with apparent molecular masses of 18 and 14 kDa, respectively. In conclusion, our present observations demonstrate the ability of IL-1 to 1) inhibit the steady state levels of transcripts corresponding to IGFBP-4 and -5 in a time-dependent, relatively specific, and receptor-mediated fashion; 2) suppress the accumulation of the corresponding IGFBP proteins; and 3) stimulate the activity of the IGFBP-5-directed (but not IGFBP-4) endopeptidase, a posttranscriptional phenomenon. Our findings also suggest, by inference, that the IL-1beta-mediated inhibition of IGFBP-4 and -5 transcripts is due in part to a decrease in the rate of transcription of the corresponding genes and not to a change in the stability of the relevant messenger RNAs. Consequently, the ability of IL-1 to influence ovarian IGFBP economy appears multifaceted, comprising both transcriptional and posttranscriptional effects. To the extent that IGFBP-4 and -5 constitute atretogenic agents, our present findings support the view that IL-1beta may play an antiatretic role in the context of ovarian physiology.

Elevated levels of the IGF-binding protein protease MMP-1 in asthmatic airway smooth muscle

We have previously demonstrated that the asthma-associated proinflammatory eicosanoid leukotriene D4 (LTD4) is co-mitogenic with insulin-like growth factors (IGFs) in airway smooth-muscle (ASM) cells in vitro. This synergistic effect of LTD4 and IGF on ASM cell growth involves proteolysis of ASM-produced IGF binding proteins (IGFBPs), which are cell growth-inhibitory proteins. We also identified this IGFBP protease to be the matrix metalloproteinase-1 (MMP-1), and showed that this enzyme had a significant role in modulating IGF action in ASM cells. In the present study, we tested the hypothesis that ASM hyperplasia in vivo involves induction of MMP-1 leading to IGFBP proteolysis. We detected the presence of MMP-1 and measured its levels in human airway tissue sections prepared from nonasthmatic and asthmatic subjects. Six nonasthmatic and six asthmatic airway tissue samples were analyzed for immunoreactive MMP-1 through an immunohistochemical detection method. Both the bronchial and tracheal smooth-muscle cells from different regions of the same sample were examined and documented. The immunostaining for MMP-1 was significantly elevated in both the bronchial and tracheal smooth-muscle cells of the airway sections from asthmatic samples relative to that of the nonasthmatic samples. The differences in levels of MMP-1, IGFBP-2, IGFBP-3, and IGFBP proteolytic activity were quantified using densitometric analyses of the ASM tissue extracts that were separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The MMP-1 levels in the asthmatic airway tissue extracts were 12-fold higher than those found in control samples. In addition, IGFBP-2 and IGFBP-3, which we have previously demonstrated to be proteolytic substrates of MMP-1, were found to be cleaved in asthmatic airway tissue extracts. Furthermore, the asthmatic airway extracts contained IGFBP proteolytic activity that was shown by immunodepletion studies to be due to MMP-1. These observations demonstrate that MMP-1 may play a significant role in inducing ASM hyperplasia and airway obstruction in asthma by modulating the IGF axis.

Characterization and hormonal regulation of a rat ovarian insulin-like growth factor binding protein-5 endopeptidase: an FSH-inducible granulosa cell-derived metalloprotease

Previous studies established the existence of an FSH-inducible rat granulosa cell-derived insulin-like growth factor binding protein (IGFBP)-5 endopeptidase. It was the objective of this communication to characterize this activity in some detail. Exposure of [125I]rhIGFBP-5 substrate to media conditioned by FSH-treated granulosa cells (a cell-free assay) produced two rhIGFBP-5 cleavage products (estimated size 19.5 and 17.5 kDa). The acquisition of IGFBP-5 endopeptidase activity in culture proved FSH (or PMSG) to be dose and time dependent. The addition of oFSH or rhFSH to the cell-free assay in turn, proved without effect on IGFBP-5 endopeptidase activity, thereby arguing against the possibility of an FSH receptor-independent phenomenon or of contaminating pituitary-derived contribution. The ability of FSH to induce IGFBP-5 endopeptidase activity proved relatively specific in that other granulosa cell agonists such as activin-A, IGF-I, GnRH, interleukin-1beta, TNF alpha, TGF beta1, EGF, or endothelin-1 failed to do so. However, the concurrent provision of GnRH, TNF alpha, EGF, or endothelin-1 proved inhibitory to the IGFBP-5 endopeptidase-inducing property of FSH. Activin-A and TGF beta1 in turn further stimulated the FSH effect. Sensitivity to EDTA, 1,10 phenanthroline, and high concentrations (> or = 0.1 mM) of Zn2+ suggested a Zn2+ metalloprotease. Insensitivity to TIMP-1 and TIMP-2 argued against a matrix metalloprotease (MMP). Relative insensitivity to PMSF, AMPSF, aprotinin, TPCK, and benzamidine argued against the possibility of a serine protease. Insensitivity to pepstatin A and E64 argued against aspartic and cysteine proteases, respectively. Insensitivity to plasminogen activator inhibitor-1 (PAI-1) and the presumed lack of free plasminogen in serum-free culture media argued against plasmin. Proteolysis was completely inhibited over the acid pH range but proceeded unencumbered at neutral and basic pH. Competition studies using unlabeled IGFBPs (1-6) as well as cell-free proteolysis assays of [125I]-labeled IGFBP-1, 2, 3, and 6 suggested a significant level of specificity for the FSH-induced/IGFBP-5-directed endopeptidase. Centricon-mediated fractionation of FSH-conditioned media revealed the IGFBP-5 endopeptidase activity in the fraction representing proteins of molecular weight >100K. Taken together, these observations document a secreted, granulosa cell-derived, high molecular weight, FSH-inducible, IGFBP-5-selective, neutral/basic pH-favoring, non-MMP Zn2+ metalloprotease.

Interferon-gamma and activin A promote insulin-like growth factor-binding protein-2 and -4 accumulation by human luteinizing granulosa cells, and interferon-gamma promotes their apoptosis

Insulin-like growth factor (IGF)-binding proteins (IGFBPs) antagonize IGF and gonadotropin actions on granulosa cells. Human atretic follicles express IGFBP-2 in granulosa cells more strongly and contain higher levels of IGFBP-2 and IGFBP-4 than healthy follicles. We studied the effects of interferon-gamma (IFN gamma) and activin A, which decrease progesterone accumulation, on granulosa cell IGFBP production and apoptosis. Conditioned media from luteinizing granulosa cells cultured with IFN gamma or activin A and/or LH were subjected to ligand blotting; northern blots of total ribonucleic acid (RNA) from these cells were probed for IGFBP-2 and -4. Apoptosis was measured by in situ DNA end labeling. LH decreased medium IGFBP-2 to 21% of the control value. Although IFN gamma did not alter basal medium IGFBP-2, in the presence of LH it increased IGFBP-2 3.4-fold, with parallel changes in messenger RNA levels. Activin A also tended to increase medium IGFBP-2 in LH-treated cultures. In conditioned medium, IGFBP-4 was consistently decreased by LH, whereas both IFN gamma and activin A increased IGFBP-4 and decreased IGFBP-4 protease activity. Both LH and IFN gamma modestly stimulated IGFBP-4 messenger RNA levels. Follistatin antagonized the action of activin A, but not that of IFN gamma. IFN gamma, but not activin A, increased granulosa cell apoptosis. In conclusion, IFN gamma produced by activated lymphocytes may decrease endogenous IGF activity through stimulation of IGFBPs and may promote apoptosis of granulosa-lutein cells in vivo and, thus, luteal regression. Activin A similarly promotes IGFBP accumulation, but it does not promote apoptosis.

Steroid-level response to insulin-like growth factor-1 in oocytes matured in vitro

The objective was to establish the influence of insulin-like growth factor-1 (IGF-1) on steroid production and nuclear maturation during oocyte in vitro maturation (IVM). Immature-selected rabbit follicular oocytes, divided as cumulus-oocyte complexes (COC) and denuded oocytes (DO), were cultured in Brackett's medium with different concentrations of IGF-1 at 0, 50, 100 and 200 ng/ml. After 8 and 16 h of culture, the oocytes were assessed for nuclear maturation by acetic-orcein stain, and media were analyzed by enzyme-immunoassay (EIA) for 17 beta-estradiol (E), progesterone (P), androstenedione (A) and testosterone (T) content. After culture treatments with IGF-1 significantly increased (P < 0.01) the incidence of nuclear activation (germinal vesicle breakdown stage, GVBD) and nuclear maturation (metaphase II stage); maximum stimulation occurred at 100 ng IGF-1/ml (86.9 vs. 49.3% in control). Compared to controls, the presence of IGF-1 in cultures was associated with a significant increase of E and A production by COCs (P < 0.01). However, P and T levels were not significantly influenced by the IGF-1. In addition, positive correlations between E/T and E/A ratios and nuclear maturation rates were only found in the IGF-1 treatments. Regarding the DOs, neither positive effects in nuclear maturation rates nor increase of steroid levels in culture were observed for any treatment. These results suggest that: (1) IGF-1 had a significant effect on E and A production during oocyte maturation; (2) the addition of IGF-1 enhanced nuclear maturation significantly in rabbit oocytes; and (3) all these effects are only possible in oocytes surrounded by cumulus cells.

The mouse intraovarian insulin-like growth factor I system: departures from the rat paradigm

Although the rat intraovarian insulin-like growth factor I (IGF-I) system is well documented, the increasing availability of null mouse mutants for components of the IGF system necessitates characterization of the mouse model as well. Therefore, we undertook to define the components of the mouse intraovarian IGF-I system and to examine its operational characteristics. The cellular pattern of ovarian gene expression was comparable in the immature rat and mouse for IGF-I and the type I IGF receptor. In both species, IGF-I messenger RNA (mRNA) is selectively expressed by granulosa cells in growing, healthy appearing follicles. Type I IGF receptor mRNA was also concentrated in granulosa cells, but was uniformly expressed in all follicles large and small, healthy and atretic appearing alike. Cellular patterns of IGF-binding protein (IGFBP) gene expression were similar in mouse and rat, except in the case of IGFBP-2. IGFBP-2 mRNA was localized to the mouse granulosa cell, in contrast to its concentration in the rat thecal-interstitial compartment. This difference in IGFBP expression pattern was also noted in cultured mouse and rat granulosa cells. Although immunoreactive IGFBP-4 (24 and 28 kDa) and IGFBP-5 (29 kDa) were shared by both species, the cultured mouse granulosa cell also featured immunoreactive IGFBP-2 (30 kDa). The mouse paradigm further differed from its rat counterpart in that a maximal dose of FSH, previously shown to suppress the elaboration of rat granulosa cell-derived IGFBPs, was without effect. The addition of IGF-I proved stimulatory to the accumulation of the 28- to 29-kDa IGFBPs, as previously reported for the rat. However, IGF-I proved inhibitory to the accumulation of the 24-kDa IGFBP (presumptive nonglycosylated IGFBP-4); no consistent effect was reported for the rat model. Functional comparisons of mouse and rat ovarian cell cultures revealed qualitatively comparable FSH-stimulated steroidogenesis, disposition of radiolabeled pregnenolone, IGF-I-amplified FSH action, and IGFBP-mediated antigonadotropic activity. These findings indicate that the mouse intrafollicular IGF-I system differs from the rat paradigm in both the makeup and regulation of granulosa cell-derived IGFBPs as well as in the intensity and character of the steroidogenic process. Studies employing the mouse model must take into account these important distinctions relative to the more established rat paradigm.

Local control of ovarian steroidogenesis

A number of putative paracrine factors are now thought to interact with FSH in the control of ovarian steroidogenesis. The relative importance of these factors remains to be determined, but the presence of the insulin-like growth factors and their binding proteins and the mechanism of control of the latter through the local production of proteases suggests a role for this system in folliculogenesis. We have demonstrated over-production of steroid hormones in tissue from women with polycystic ovaries. Theca cells in monolayer culture produced excessive amounts of progesterone and androstenedione and granulosa cell oestradiol production was considerably enhanced in response to FSH. Recent evidence points to a genetic defect in the expression or translation of steroidogenic hormones as a cause of excess androgen production, but the gene or genes involved has not been established. Data from our group suggest that granulosa cells from anovulatory polycystic ovaries are prematurely matured and we hypothesize that this is due to the interaction of the raised circulating insulin levels with LH in these follicles, an interaction that results in arrested follicular growth.

Interactions between insulin-like growth factor-I (IGF-I) and the renin-angiotensin system in follicular growth and ovulation

The interactions between insulin-like growth factor-I (IGF-I) and the renin-angiotensin system (RAS) in follicular growth and ovulation were studied with the use of an isolated perfused rabbit ovary preparation. Ovulation failed to occur in either control ovaries or the experimental ovaries perfused with IGF-I in a concentration of 1, 10, or 100 ng/ml in the absence of gonadotropin. Exposure to IGF-I stimulated the secretion rate of angiotensin II-like immunoreactivity (Ang II-IR) in perfused rabbit ovaries in a dose-dependent manner. The percent increase in follicle diameter in ovaries perfused with IGF-I for 12 h was significantly correlated with the secretion rate of Ang II-IR at 12 h after exposure to IGF-I. The addition of IGFBP-3 to the perfusate did not induce ovulation in the absence of gonadotropin, but exposure to IGFBP-3 inhibited hCG-induced ovulation in a dose-dependent manner. In addition, IGFBP-3 significantly reduced the ovarian secretion rate of Ang II-IR and prostaglandins stimulated by hCG administration. Intrafollicular plasminogen activator (PA) activity significantly increased within 4 h after exposure to 100 ng/ml of IGF-I, compared with that in control ovaries perfused with medium alone. The concomitant addition of IGFBP-3 to the perfusate significantly reduced the IGF-I-stimulated PA activity in the preovulatory follicles at 4, 6, and 8 h after exposure to IGF-I. However, IGFBP-3 alone affected neither the ovarian secretion rate of Ang II-IR nor intrafollicular PA activity. Exposure to streptokinase, an exogenous PA, in vitro stimulated both follicular growth and the intrafollicular Ang II-IR content. In conclusion, IGF-I enhances both ovarian Ang II production and follicular development by stimulating intrafollicular PA activity.

Interrelationships between follicle stimulating hormone and the growth hormone--insulin-like growth factor--IGF-binding proteins axes in human granulosa cells in culture

As it has been hypothesized that IGF-binding proteins (IGFBPs) may have a role as autocrine/paracrine factors in regulating the local actions of the insulin-like growth factors (IGFs) in the ovary, we studied the production of the IGFBPs by human granulosa cells (GC) in culture and the role of IGFBP-3 in the modulation of ovarian cell responsiveness to IGF-I and FSH. To this purpose, human luteinizing GC were cultured in serum-free conditions for 24 h and subsequently submitted to increasing concentrations (2-8 nmol/l) of recombinant non-glycosylated or partially glycosylated IGF-BP-3 for 48 h, in the presence or absence of IGF-I, des(1-3)IGF-I- a truncated analog of human IGF-I with markedly reduced binding ability to IGFBPs - and FSH (5-20 mIU/ml). The results demonstrate that human GC release IGFBP-1-2 and -3 into the medium, and that FSH is able to inhibit this release, while GH is clearly inhibitory on IGFBP-1 and stimulatory on IGFBP-3. Both IGF-I and des(1-3)IGF-I significantly (p < 0.001) stimulate E2 production by human GC in culture in a manner comparable to that of FSH in the dose range used. Preincubation for 2 h at 22 C with IGFBP-3, to allow the formation of the IGF-IGFBP complex, drastically reduced the stimulatory effect of IGF-I but not that of des(1-3)IGF-I. IGFBP-3 was also able to inhibit the stimulatory effect of FSH. These data show that: i) the IGF peptide is less active when bound to IGFBP-3; ii) as IGFBP-3 does not affect the potency of des(1-3)IGF-I, its inhibitory action is exerted upstream of the membrane receptor binding; iii) as the action of IGFBP-3 is exerted by binding the IGF peptide, its inhibitory effect on FSH points out the role of the locally produced IGF-II in potentiating the FSH action on human GC.

Insulin-like growth factor receptors and binding proteins

The insulin-like growth factor receptors are integral membrane proteins and demonstrate separate, but important effects on the regulation of cellular processes. The IGF-I receptor signals multiple cascades via its inherent tyrosine kinase activity. The IGF-II/M-6-P receptor on the other hand is primarily involved in targeting of enzymes to various subcellular compartments. In contrast, the insulin-like binding proteins are secreted by the cells and accumulate in the extracellular matrix or on the external surface of the cell. They are also involved in regulating cellular processes more indirectly. They modulate the interactions of the IGFs with their receptors, and in addition, may have some IGF-independent effects probably by direct interaction with integrin and other cell membrane receptor proteins. The recent studies, as outlined in this review, strongly suggest an important, if not essential role for the IGF system in normal physiology and disease states. The challenge now is to define the mechanisms involved in these effects. More studies are required to fully understand the post-receptor mechanism involved in IGF-I receptor signal transduction and the mechanisms whereby the IGFBPs exert their interesting effects. Understanding these mechanisms will enable investigators to create new therapeutic modalities for diseases that are affected by the IGF system.

Regulation of IGF binding proteins by FSH in human luteinizing granulosa cells

OBJECTIVE

To evaluate the regulation of the secretion of insulin-like growth factor (IGF) binding proteins (IGFBPs) by FSH in human luteinizing granulosa cells.

DESIGN AND RESULTS

Luteinizing granulosa cells were incubated with and without FSH. Levels of IGFBP-1 and -3 in the medium were measured by EIA and RIA, respectively and binding activities of these IGFBP were evaluated by Western ligand blot. FSH inhibited the secretion of IGFBP-1 dose dependently. FSH did not inhibit the secretion of immunoreactive IGFBP-3, but inhibited the binding activity of IGFBP-3. To assess the protease activity, 125I-IGFBP-3 was incubated with the cultured medium. 125I-IGFBP-3 degraded into small fragments when it was incubated with the cultured medium treated with FSH.

CONCLUSIONS

FSH enhances the action of IGF-I in human granulosa cells by inhibiting the secretion of IGFBP-1 and the binding activity of IGFBP-3 by stimulating the proteolysis of IGFBP-3.

The ovarian insulin and insulin-like growth factor system with an emphasis on domestic animals

Insulin and insulin-like growth factors (IGFs) have direct effects on cultured ovarian cells. These effects include stimulation of granulosa cell mitogenesis, granulosa and luteal cell progesterone production, and thecal cell androgen production and appear similar among species. However, species differences exist with regard to insulin and IGF-I effects on granulosa cell estradiol production. In addition to endocrine effects of insulin and IGFs, IGFs are produced by granulosa, thecal, and luteal cells, allowing for an intraovarian autocrine and paracrine system. Granulosa, thecal, and luteal cells contain receptors for insulin and IGFs, and these receptors appear to mediate the effects of insulin and IGFs. Adding to the complexity of the regulatory role of IGFs is the presence of IGF-binding proteins (IGFBPs) within the ovary. These IGFBPs are produced by granulosa, thecal, and luteal cells, and their production is hormonally regulated. Evidence for a coherent mechanism by which insulin, IGFs, and IGFBPs interact and regulate ovarian function in vivo has yet to be found.

Insulin-like growth factor-1 (IGF-1) stimulates the IGF binding protein system in rat theca interstitial cells

There has been considerable interest in rat ovarian insulin-like growth factor binding proteins IGFBPs because they are potent inhibitors of FSH action.In situ, IGFBP-2 and -4 and IGFBP-3 mRNAs are expressed in rat theca interstitial (TIC) and theca lutein cells respectively. Although much is known about IGFBPs in rat TIC at the mRNA level, the synthesis and regulation of IGFBP proteins remain poorly understood. The purpose of this study was to identify the species of IGFBPs produced by TIC and to determine the effects of LH and IGF-1 on their expression. This was accomplished by culturing rat TIC for 2 days in serum-free medium with graded doses of LH and/or IGF-I, and measuring IGFBP mRNAs in the cells and IGFBP proteins in the conditioned media by RT-PCR and Western immunoblotting respectively. The RT PCR analysis identified strong bands for IGFBP-2 and -4 mRNAs in TIC. In some treatments, the mRNAs for IGFBP-3 and -6 were also identified, but transcripts for IGFBP-1 and -5 were undetectable. Two species of IGFBPs were detected in the conditioned media of control (untreated) TIC, the 31 kDa IGFBP-2 and the 24 kDa (non-glycosylated) and 28 kDa (glycosylated) forms of IGFBP-4. There was no detectable IGFBP-5 and barely detectable amounts of IGFBP-3 and -6 in the conditioned media. Treatment with LH (0.2-20 μU/ml) caused no significant changes in the levels of the 31 kDa IGFBP-2 and the 24 kDa and 28 kDa IGFBP-4 bands, and there was no detectable IGFBP protease activity. In contrast, IGF-I (100 ng/ml) stimulated the expression of IGFBP-2, IGFBP-4 and a 17.5 kDa IGFBP-4 fragment. The immunoreactive IGFBP-4 fragment suggests the media contained an IGFBP-4 protease. The IGF-I effects were dose dependent (ED(50)=12.4±3.3 ng/ml). Co-treating TIC with LH (0.2-20 μU/ml) caused no significant change in the activity of IGF-I in stimulating the expression of IGFBP-2, IGFBP-4 and IGFBP-4 protease. We have demonstrated that IGF-I acts directly on rat TIC to stimulate the expression of the intrinsic IGFBP system. LH, either alone or together with IGF-I, did not significantly change the expression of TIC IGFBP proteins. Therefore, we hypothesize that IGF-I, but not LH, may be a physiologically important regulator of the IGFBP system in rat TIC. Because IGF-I is a potent stimulator of theca function, changes in the expression of this intrinsic IGFBP system could have new implications for ovarian androgen production, both at the physiologic and pathophysiologic levels.

Gonadotropin-releasing hormone overcomes follicle-stimulating hormone's inhibition of insulin-like growth factor-5 synthesis and promotion of its degradation in rat granulosa cells

The effect of a gonadotropin-releasing hormone-agonist (GnRH-a) on the synthesis of insulin-like growth factor-binding protein-5 (IGFBP-5), a physiological marker for atresia, was investigated. Granulosa cells obtained from diethylstilbestrol (DES)-treated immature female rats were cultured in serum-free medium for 72 h with GnRH-a and the conditioned media were subjected to immunoblot analysis using rat IGFBP-5 specific antibody. GnRH-a caused a dose-dependent (ED50 = 8.6 x 10(-11) M) accumulation of IGFBP-5, which migrated as 35 (non-glycosylated) and 36 kDa (glycosylated) bands under reducing conditions. A maximally effective dose of GnRH-a (10(-9) M) caused a 4-fold increase in IGFBP-5 accumulation. In contrast, increasing doses of porcine follicle-stimulating hormone (pFSH) caused a biphasic effect on IGFBP-5 accumulation. A low dose of pFSH (0.25 ng/ml) increased and higher doses of pFSH (22.5 ng/ml) decreased the 35 and 36 kDa IGFBP-5 bands. In the presence of high doses of pFSH (20.75 ng/ml), a 22 kDa band corresponding to a cleaved IGFBP-5 fragment appeared in the media. When the granulosa cells were cultured with a saturating dose of pFSH, co-addition of GnRH-a dose dependently inhibited the FSH effects (ED50 = (2.3-3.7) x 10(-10) M). The GnRH-a effects were completely blocked by co-incubation with GnRH-antagonist. IGFBP-5 mRNA accumulation levels were increased by GnRH-a in a dose dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of phorbol ester and staurosporine on the actions of insulin-like growth factor-I on rat ovarian granulosa cells

Insulin-like growth factor I (IGF-I) is able to stimulate ovarian granulosa cell steroidogenesis induced by gonadotopins. This gonadotropin-induced potentiation of IGF-I action appears to be due, at least in part, to a gonadotropin-induced increase in membrane-bound IGF-I receptor number and/or decrease in extracellular IGF binding proteins (IGFBPs). Protein kinase C (PKC) has recently been reported to inhibit gonadotropin-induced steroidogenesis in rat ovarian granulosa cells. The role of PKC in the effects of IGF-I on gonadotropin action, however, is unknown. In this study, the effects of phorbol 12-myristate 13-acetate (PMA, a PKC activator) and staurosporine (ST, a PKC inhibitor) on IGF-I action were studied using immature rat ovarian granulosa cells. Activation of PKC by PMA did not affect steroidogenesis or cAMP secretion in cells treated with or without IGF-I. On the other hand, inhibition of PKC by ST alone (10(-9)-10(-7)m) led to an increase in progesterone production in a dose- and time-dependent manner without affecting cAMP secretion. In the presence, but not absence, of ST, IGF-I was able to stimulate progesterone production in the absence of any gonadotropin. PMA decreased ST-induced steroidogenesis and essentially abolished ST-potentiated IGF-I stimulation of steroidogenesis, suggesting the effects of ST on IGF-I action involved a PKC-dependent mechanism. Unlike gonadotropin, ST did not change IGF-I receptor binding. However, ST significantly decreased a major IGF binding protein (IGFBP, ∼30kDa) which is likely to be IGFBP-5, whereas it increased a minor IGFBP (∼24kDa) which is likely to be IGFBP-4. Both effects of ST were dose- and time-dependent. Furthermore, ST inhibited the expression of mRNA for IGFBP-5 suggesting that ST decreased IGFBP-5 levels by inhibiting its transcription and/or decreasing the stability of its mRNA. Interestingly, ST also decreased mRNA levels of IGFBP-4 despite a significant increase in secreted IGFBP-4 levels. The mechanisms involved are not known. Activation of PKC by PMA had no acute effect on these IGFBPs. The regulation by ST of IGFBPs was not antagonized by PMA, and was not affected by PKC-down regulation. Thus, it is likely that ST induces granulosa cell steroidogenesis, potentiates the IGF-I stimulation of steroidogenesis and regulates IGFBP via both PKC-dependent and -independent pathways.

Ovarian control of follicle development

A variety of ovarian autocrine and paracrine factors may modulate folliculogenesis and steroid production. The developmental program that leads to the production of a dominant follicle involves a precise quantitative and temporal pattern of expression of a large number of genes. Follicle-stimulating hormone plays an essential role in this process, and no other ligand by itself can serve in this regulatory capacity. It is clear that a variety of growth factors can modulate follicle-stimulating hormone action by autocrine and paracrine mechanisms. Advances in the understanding of the role of growth factors, particularly the family of insulin-like growth factor-related proteins, in regulating follicle-stimulating hormone action are discussed. It is likely that complex interactions exist between follicle-stimulating hormone and the growth factors. Significantly, growth factor regulation by pituitary gonadotropins is probably a central feature of their expression. With increased understanding of the ovarian control of follicle development, it is hoped that newer and more effective regimens for synchronous follicular and oocyte maturation can be realized.

Ovarian follicular growth, ovulation and atresia. Endocrine, paracrine and autocrine regulation

This chapter describes a finely tuned series of events that results in ovarian morphological changes including follicular growth, dominant follicle selection, oocyte development, ovulation, and corpus luteum formation. These changes are under the obligate control of the pituitary gonadotropins FSH and LH. The signaling mechanisms whereby the gonadotropins stimulate these changes in the ovary are now well described. The gonadotropin membrane receptors have been cloned and the cellular events proceeding from receptor binding to phosphorylation of protein gene regulators, such as CREB, have been elucidated. A whole series of intraovarian paracrine and autocrine regulators have been described as having the capability of "fine tuning" the effects of gonadotropins (see Tables I and II), and they are likely involved in dominant follicle selection and the demise of the corpus luteum. The roles of the individual paracrine regulators are, as of yet, not well known, but the IGF system offers an attractive paradigm for these intraovarian factors. Lastly, we have described the explosion of data on intracellular and intranuclear regulators. The challenge for us will be to understand the physiological significance of the seemingly unlimited number of regulatory possibilities. Much has been learned concerning the regulation of the morphological changes seen in the ovary, but much more remains to be elucidated.

IGF-binding proteins are differentially regulated in an ovarian granulosa cell line

We have recently established an immortalized granulosa cell line as a model system to investigate ovarian function, with particular emphasis on the insulin-like growth factor (IGF) regulatory system. Previous results have shown that these cells express mRNAs for IGF-binding proteins (IGFBPs)-2 to -5. These IGFBPs are also detected by ligand blots. The current work evaluated the regulation by the IGFs and cAMP on the IGFBPs and their mRNAs and compared the findings to that in primary culture. Our results indicate that levels of the IGFBPs are controlled, in part, by expression of the mRNAs. However, evidence for post-transcriptional regulation was also discovered. IGFBP-3 was stimulated by IGF-I, IGFBP-4 by forskolin, and IGFBP-5 by IGF-I. IGFBP-2, -3, and -4 are expressed under basal conditions whereas IGFBP-5 is only detectable after IGF-I induction. An alteration in the biphasic actions of cAMP in this cell line, as compared to primary culture, was evident.

IGF-I stimulates granulosa cell-derived insulin-like growth factor binding protein-5: evidence for medication via type I IGF receptors

Although the precise role of insulin-like growth factor binding proteins (IGFBPs) in ovarian physiology remains a matter of study, existing data suggest a possible antigonadotropic role in the context of follicular atresia. Given the above and the need for improved understanding of the regulation of ovarian IGFBPs, we have set out to explore the ability of IGF-I to modulate IGFBP levels in cultured rat granulosa cells. Specifically, granulosa cells (5 x 10(5) viable cells/dish) from immature (23-25 days old), estrogen-primed rats were cultured under serum-free conditions for 72 h in the absence or presence of IGF-I. At the conclusion of this incubation period, media samples were collected and subjected to Western ligand blotting. Treatment with IGF-I (100 ng/ml) resulted in a substantial (P < 0.05) increase in the accumulation of IGFBP-5, the major 28-29 kDa IGFBP species. Subsequent studies revealed this effect of IGF-I to be both dose- and time-dependent. A similar effect was noted for insulin at dose levels 1-10 micrograms/ml at which cross-reaction with the type I IGF receptor (but not with IGFBPs) has been amply documented. Des (1-3) IGF-I, a type I receptor-selective ligand with markedly reduced avidity for IGFBPs, proved substantially more potent (as a promoter of IGFBP-5 accumulation) than its native counterpart. In contrast, treatment with IGF-II or [Leu27]IGF-II, type II IGF receptor-selective ligands, yielded a more limited effect on IGFBP-5 accumulation in keeping with an overall rank order of potency of des (1-3) IGF-I > IGF-I > IGF-II > or = [Leu27]IGF-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of insulin-like growth factors (IGFs) and IGF binding proteins -1, -2 and -3 in human placenta and fetal membranes

Insulin-like growth factor (IGF) I and II are synthesized within the placenta and are believed to play an important role in the regulation of placental growth and endocrine function. IGF bioavailability is determined at a cellular level by several specific binding proteins (IGF BPs), which are widely but selectively distributed in all developing tissues. We have used immunohistochemistry to localize IGF I and II peptides, and IGF BP-1, -2, and -3 in human placentae, fetal membranes and umbilical cord at 6-8 weeks after therapeutic termination and at term after spontaneous delivery. Primary antisera were directed against human IGF I, human IGF BP-1, bovine IGF BP-2, and human IGF BP-3 respectively. Immunoreactive IGF BP-2 was found in association with the syncytiotrophoblast, intermediate trophoblasts of the fetal villi and chorion, amnion and decidua; while weaker staining was seen in some but not all cytotrophoblasts. A similar but less intense staining pattern was observed for IGF BP-1 and IGF peptides in placenta and amnio-chorion. Strong immuno-staining for IGF BP-1 was seen in decidual cells. No immunoreactive IGF BP-3 was found in placenta or membranes. A co-distribution of IGF BP-2, BP-1 and IGF peptides in placenta suggests a role for these IGF BPs in determining the localization of the IGFs for actions on target tissues.

Conventional and nonconventional uses of growth hormone

Although GH has been available as a therapeutic agent for the GH-deficient child for more than 30 years, the conditions of its use have yet to be optimized. The availability of biosynthetic material has provided researchers with the opportunity to develop the protocols necessary to begin to finally answer the most fundamental questions pertaining to dose, frequency, and duration of treatment. It has also permitted the initiation of prospective trials in a large number of conditions that result in childhood short stature, with the expectation that some or many of them will be treated effectively and safely. Finally, it has opened the door to an entire spectrum of potentially new uses of GH and other growth factors for so-called nonconventional indications. That these have implications that range from the short-term rapid healing of a burn graft site, to the more efficient induction of ovulation, to the long-term preservation of lean body mass has excited the interest of investigators in many fields of medicine and physiology. Thus, the recent progress reported in this paper is really the beginning of the new research that will take place with GH and growth factors.

Granulosa cell-derived insulin-like growth factor (IGF) binding proteins are inhibitory to IGF-I hormonal action. Evidence derived from the use of a truncated IGF-I analogue

An increasing body of information now suggests that insulin-like growth factor (IGF) binding proteins (BPs) may serve as antigonadotropins at the level of the ovary. It is the objective of the present communication to evaluate the functional role of endogenous (granulosa cell-derived) IGFBPs by exploiting the unique properties of des(1-3)IGF-I, a naturally occurring IGF-I analogue characterized as a weak ligand of IGFBPs but not of type I IGF receptors. Given IGFBP-replete circumstances, des(1-3)IGF-I proved more potent (10-fold) than its intact counterpart in promoting the follicle stimulating hormone (FSH)-stimulated accumulation of progesterone by cultured rat granulosa cells. In contrast, des(1-3)IGF-I proved virtually equipotent to the unmodified principle under IGFBP-deplete circumstances. Taken together, these findings are in keeping with the notion and that the apparently enhanced potency of des(1-3)IGF-I (under IGFBP-replete conditions) is due to its diminished affinity for endogenously generated IGFBPs and that rat granulosa cell-derived IGFBPs are inhibitory to IGF (and thus inevitably to gonadotropin) hormonal action. Accordingly, the reported ability of gonadotropins to attenuate IGFBP release by granulosa cells may be designed to enhance the bioavailability of endogenously generated IGFs in the best interest of ovarian steroidogenesis.

Luteinizing hormone induction of the cholesterol side-chain cleavage enzyme in cultured immature rat Leydig cells: no role of insulin-like growth factor-I?

Long-term inductive effects of luteinizing hormone (LH) on cholesterol side-chain cleavage (CSCC) enzyme activity were studied, using cultured Leydig cells isolated from 21-day-old rats. Particular reference was given to the role of insulin-like growth factor-I (IGF-I) as an autocrine or paracrine modulator or as an essential extracellular mediator of LH action. The CSCC enzyme activity was measured using an excess of 22(R)-hydroxycholesterol as substrate to saturate the enzyme, and inhibitors of pregnenolone metabolism to concentrate all the products of the enzyme reaction in pregnenolone. The rate of sterol conversion into pregnenolone (CSCC enzyme activity) reflected the amount of cytochrome P-450scc (P-450scc), as was shown by Western blotting. In cells cultured without LH, the CSCC enzyme activity decreased to 10% on day 7 of the culture period. In the presence of various doses of LH ranging from 0.01 to 100 ng/ml, the CSCC enzyme activity also diminished during the first 3 days of culture, but during the following days, the amount of CSCC enzyme was stimulated by LH. In contrast to the absence of any LH effect on the activity of the CSCC enzyme during the first days of the culture, the endogenous steroid production (no added 22(R)-hydroxycholesterol) could be stimulated at least 10-fold by high doses of LH. When LH (1 ng/ml) was added to cells which had been cultured for 7 days without hormones, CSCC enzyme activity was elevated 8-fold after 4 days of exposure of LH. These effects of LH could be mimicked by dbcAMP (0.5 mM). No evidence could be provided that IGF-I plays any role in the LH induction of the CSCC enzyme; neither the addition of exogenous IGF-I or analogs that do not bind to IGF-I binding proteins (IGFBPs) nor the inactivation of endogenous IGF-I action (through binding to IGFBP and antibodies to IGF-I or via masking of IGF-I receptor by antibodies) could influence the LH induced CSCC enzyme activity. The present data raise the question under which conditions IGF-I is capable of modulating Leydig cell steroidogenesis.

Gonadotropin and cAMP modulation of IGE binding protein production in ovarian granulosa cells

Porcine granulosa cells (GC) produce insulin-like growth factor (IGF) binding protein (BP)-3 and IGFBP-2 in culture. A gonadotropin, follicle-stimulating hormone (FSH), dramatically inhibited GC production of these IGFBPs in control cultures and in cultures stimulated by insulin plus epidermal growth factor (EGF) or IGF-I plus EGF. Stimulators of adenylate cyclase (forskolin, cholera toxin) and a derivative of adenosine 3',5'-cyclic monophosphate (cAMP), 8-bromoadenosine 3',5'-cyclic monophosphate, inhibited IGFBP synthesis in a manner similar to FSH. In contrast, the antagonist of cAMP action, (R)-p-adenosine 3',5'-cyclic phosphorothioate [(R)-p-cAMPS], significantly stimulated production of IGFBP-3 and IGFBP-2 compared with controls. This stimulatory effect of (R)-p-cAMPS was counteracted by cotreatment with FSH in a dose-dependent manner. Finally, treatment of GC cultures with FSH plus 3-isobutyl-1-methylxanthine resulted in a significant reduction in cellular content of mRNA coding for IGFBP-3 with no change in IGFBP-2 mRNA. In summary, agents that elevate intracellular cAMP were found to mimic the effects of FSH on IGFBP production.

Similar distribution of insulin-like growth factor binding proteins-1, -2, -3 in human fetal tissues

The actions of insulin-like growth factors (IGFs) are modulated by several specific binding proteins (IGF BPs). Since the anatomical distribution of IGF BPs is likely to dictate IGF bioavailability we used immunocytochemistry to localize IGF BP-1, -2, and -3 in early second trimester human fetal tissues. Primary antisera were directed against hIGF BP-1, bIGF BP-2 and hIGF BP-3 respectively, and showed less than 5% cross-reaction with heterologous IGF BP species. The distribution of immunopositive staining was similar for each IGF BP in many tissues being prominent in the epithelial lining of the gut, kidney and lung; in epidermis, adrenal cortex and pancreatic endocrine tissue; and in association with membranes of skeletal muscle fibres and cardiocytes. Unlike IGF BP-1 -2, IGF BP-3 was barely detectable in liver and absent from epiphyseal chondrocytes. Conversely, IGF BP-3 alone was visualized within neurons of the cerebral cortex. The co-distribution of IGF BPs in many human fetal tissues suggests that they may co-ordinately regulate IGF bioavailability in target tissues and modify IGF: receptor interactions.