Insulin-like Growth factor-I Production Research Articles

Effect of 17 β-estradiol on the human osteosarcoma cell line MG-63

We present evidence that 17 β-estradiol (17 β-E 2) regulates 1,25(OH) 2D 3-induced alkaline phosphatase synthesis and osteocalcin secretion by the human osteosarcoma cell line MG-63. When cells were pre-treated with 17 β-E 2 for 48 h prior to treatment with 1,25(OH) 2D 3 (50 nM) for another 48 h, alkaline phosphatase activity increased by 40% ( P < 0.025) with 2 nM 17 β-E 2 and plateaued at levels of 20 and 200 nM 17 β-E 2. Under the same experimental conditions, osteocalcin secretion was enhanced by 37% ( P < 0.005) with 2 nM E 2. However, 17 β-E 2 had no effect on basal alkaline phosphatase or on osteocalcin secretion. Moreover, simultaneous addition of 17 β-E 2 and 1,25(OH) 2D 3 to cells did not result in any additional effect over l,25(OH) 2D 3 treatment alone. Tamoxifen (10 nM) inhibited 17 β-E 2-induced activities in l,25(OH) 2D 3-treated cells while not affecting control cells. Dexamethasone pretreat-ment (100 nM, 48 h) also stimulated alkaline phosphatase activity in MG-63 cells. Moreover, dexamethasone pretreatment followed by treatment with 17 β-E 2 and l,25(OH) 2D 3 gave an additive effect for alkaline phosphatase activity. 17 α-Estradiol (17 α-E 2), a less active form of estrogen, failed to modify, at low concentrations, control or l,25(OH) 2D 3-induced alkaline phosphatase synthesis and osteocalcin secretion. In fact, a 100–1000-fold higher concentration of 17 α-E 2 was necessary to reproduce the effects of 17 β-E 2 on osteocalcin secretion. The addition of insulin-like growth factor I (IGF-I) for 24 h (1–50 ng/ml) to MG-63 cells did not modify 1,25(OH) 2D 3-induced osteocalcin release from these cells. However, longer incubations with 50 ng/ml IGF-I did reproduce some of the effects observed with 17 β-E 2. Thus, the effects of 17 β-E 2 are probably not related to IGF-I production in MG-63 cells since under these conditions the addition of IGF-I alone should have produced a response at shorter incubation times and in the presence of lower concentrations of IGF-I. Since 17 β-E 2 pretreatment was necessary to observe any effects on l,25(OH) 2D 3-induced activities, we hypothesized that 17 β-E 2 regulated 1,25(OH) 2D 3 receptors in MG-63 cells. When cells were treated with 100 nM 17 β-E 2 for 48 h, the binding affinity was unchanged: 37.3 ± 1.9 versus 35.1 ± 0.4 pM for cells whether treated or not with l7 β-E 2, respectively. In contrast, a significant increase in binding capacity (B max) was noted (15 ± 3.5%; P < 0.025). These results suggest that the estrogen analogue 17 β-E 2 induces the differentiation of MG-63 cells into a more osteoblastic-like phenotype while 17 α-E 2 is without physiological effect. They also suggest that estrogens may regulate bone remodeling by modulating hormonal-induction of proteins involved in bone mineralization. This effect is indirect since it does not modify basal activities, but involves a regulation of 1,25(OH) 2D 3 receptor levels in these MG-63 cells.

Overexpression of a truncated growth hormone receptor in the sex-linked dwarf chicken: evidence for a splice mutation.

Sex-linked dwarfism in chickens is a form of GH resistance that resembles the Laron syndrome in humans. The dwarfism found in chickens is due to a mutant gene (dw) carried on the sex chromosome. The homozygous dwarf (dwdw) chicken is characterized by reductions in stature and plasma insulin-like growth factor-I (IGF-I) levels. Despite the absence of hepatic GH-binding activity, Southern blot analysis shows that there is no gross structural change in the gene for the GH receptor (GHR) in this strain of dwdw chicken. GH-dependent IGF-I production can be restored in cultured dwdw hepatocytes after transfection and transient expression of a chicken GHR (cGHR) cDNA, indicating that other factors that participate in GH-mediated IGF-I synthesis are intact. Northern blot analysis of liver, muscle, fat, and pituitary RNA from normal (DwDw) chickens shows a major transcript of 4.3 kilobases (kb) and three minor transcripts (0.8, 1.7, and 3.2 kb), which correspond to the cGHR. In contrast, the 0.8-kb transcript is the major cGHR transcript expressed in these tissues from dwdw chickens. Northern blot analysis with domain-specific probes shows that the 0.8-kb transcript in DwDw and dwdw liver contains only a small portion of the extracellular domain of the cGHR. A cDNA clone encoding this transcript has been isolated from a liver library prepared from a normal chicken.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between growth hormone and nutrition in hypophysectomized rats: body composition and production of insulin-like growth factor-I

Hypophysectomy of adult rats results in a loss of body growth which can be reversed by treatment with GH. The increased growth caused by administration of GH is accompanied by an increase in food consumption. The effects of GH and interactions with nutrition were investigated by treating hypophysectomized rats with GH and either providing unrestricted food or preventing the increased food consumption by pair-feeding with the same intake as that of the hypophysectomized animals. Over the 7-day experimental period, the GH-treated animals grew significantly when food was available ad libitum but did not gain body weight when an increase in food intake was prevented. However, there was a significant interaction between GH and nutrition on body composition; GH significantly decreased body fat and increased the protein: fat ratio only in the animals with the restricted intake. Gastrocnemius muscle weight was increased by GH regardless of food intake, but heart weight did not increase and liver weight was actually decreased by GH treatment when food intake was restricted. Serum concentrations of insulin and insulin-like growth factor-I (IGF-I) were increased by GH in the rats with food available ad libitum but not in the pair-fed rats. However, the liver concentration of IGF-I and its mRNA were increased by GH although the increase in IGF-I mRNA was modulated by the restricted food intake. The decreased weight of the liver in the pair-fed GH-treated rats, despite the increase in IGF-I mRNA, suggests that IGF-I does not influence liver growth. In the gastrocnemius muscle, however, GH increased IGF-I mRNA concentration similarly in both rats with food available ad libitum and in pair-fed rats. Decreased nutrition therefore modulated the action of GH but emphasized its nutrient partitioning effect, thus increasing the anabolic drive towards skeletal muscle growth; this appeared to be mediated by the local production of IGF-I within the muscle.

Autocrine control of wound repair by insulin-like growth factor I in cultured endothelial cells.

The repair process of the vascular endothelium is modulated by growth factors from both endogenous (within the vessel wall) and exogenous (blood borne) sources. We utilized a tissue culture model of endothelial wounding to gain further insight into the potential autocrine control of proliferation during wound repair. Cultured porcine aortic endothelial monolayers were mechanically wounded by passing a 7-mm sterile glass rod over the surface of the culture. Proliferation at the wound edge was quantified using [3H]thymidine autoradiography. In wounded cultures incubated in media supplemented with 10% fetal calf serum, 81 +/- 2% of the nuclei at the wound edge were labeled. When the cultures were incubated in serum-free media, proliferation at the wound edge was only slightly diminished with 65 +/- 3% (P < 0.05) of the cells labeled. These findings raise the possibility that there is a significant contribution from autocrine growth factors to endothelial wound repair. To evaluate the potential role of insulin-like growth factor I (IGF-I) in the wound repair process, we used a radioimmunoassay to measure IGF-I secretion. Wounded cultures exhibited a 187 +/- 58% increase in IGF-I production when compared with nonwounded cultures (P < 0.05). To determine the extent to which endogenous IGF-I mediates the proliferative response of endothelial cell monolayers to wounding, wounded cultures were incubated with inactivating concentrations of IGF-I antibody. When IGF-I antibody was present in the culture media, only 26 +/- 3% of the nuclei at the wound edge were labeled with [3H]thymidine (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin E2 rapidly stimulates insulin-like growth factor-I gene expression in primary rat osteoblast cultures: evidence for transcriptional control.

Osteoblast-enriched (Ob) cultures isolated from fetal rat bone synthesize insulin-like growth factor-I (IGF-I), which functions as a locally acting growth and differentiation factor in the skeleton. Consistent with prior studies demonstrating that IGF-I production is enhanced in bone by agents that induce cAMP, prostaglandin E2 (PGE2) stimulates both cAMP synthesis and IGF-I mRNA in Ob cells. However, little is known about how cAMP regulates IGF-I expression in this or any other cell system. In rat tissues, multiple mechanisms influence levels of IGF-I mRNA, including transcription from two promoters, differential RNA splicing and stability, and alternative RNA polyadenylation. To determine how cAMP influences IGF-I gene expression in Ob cultures, we examined the responses of these cells to treatment with PGE2. PGE2 rapidly enhanced the accumulation of both large and small IGF-I transcripts, with increases in IGF-I mRNA detected within 2 h of treatment and persisting for 24 h. Analysis of precursor RNA by a highly specific and sensitive ribonuclease protection assay demonstrated a rise in nascent IGF-I mRNA within 30 min of exposure to PGE2, with a peak stimulation of 4-fold above control levels seen by 2 h and levels remaining elevated for up to 24 h. IGF-I transcripts in Ob cells were directed only by promoter 1, the more 5' of the two rat IGF-I gene promoters. As additionally assessed using the RNA polymerase II inhibitor 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole, PGE2 treatment had little effect on IGF-I mRNA stability. In aggregate, these studies show that in fetal rat Ob cultures, PGE2 enhances IGF-I gene expression primarily through transcriptional mechanisms that are limited to a single IGF-I gene promoter. Ob cells, therefore, may be an excellent model for determining how cAMP regulates IGF-I gene transcription.

The influence of endocrine factors on the serum concentrations of insulin-like growth factor-I (IGF-I) and IGF-binding proteins.

Serum insulin-like growth factor-I (IGF-I) levels in lit (isolated GH deficiency), dw (panhypopituitarism), hyt (hypothyroidism) and cog (congenital goiter) mutant mice were found to be significantly lower than in control mice. In addition, liver and kidney IGF-I concentrations in mutants were also found to be significantly reduced compared with controls. These differences in IGF-I concentration were not observed in pg (genetic IGF receptor or post-receptor defect?) mice. These results indicated that serum IGF-I production is induced by thyroid hormones as well as by GH. Western blot analysis of serum IGF-binding protein (IGFBP) fractions revealed the following differences among the five mutants: the triplet of IGFBP-3 (42, 45 and 49 kDa) and IGFBP-4 (24 kDa) levels were significantly reduced. IGFBP-2 (32 kDa) levels were also reduced in the lit, hyt and cog mice, although the level in serum of dw mice was found to be greatly elevated. No differences in serum IGFBP levels were found in the pg mouse. Consequently, the ratio of IGFBP-3%: IGFBP-2% (the percentage of IGFBP-3 fraction of total IGFBP (IGFBP-3%) divided by that of IGFBP-2 (IGFBP-2%)) was decreased in GH-deficient mice but increased in hypothyroid mice, suggesting that IGFBP-3 and IGFBP-2 production in the liver is induced by GH and thyroid hormones respectively.

Androgen induction of steroid 5 alpha-reductase may be mediated via insulin-like growth factor-I.

The action of added insulin-like growth factor-I (IGF-I) and dihydrotestosterone (DHT) on steroid 5 alpha-reductase (5 alpha R) activity was studied using primary cultures of rat or human scrotal skin fibroblasts. Agents were added to cultured cells (2 x 10(5) cells) for 2 days, and enzyme activity was measured by the percent conversion of [3H] testosterone to DHT over a 4-h period in the absence of fetal calf serum or other growth factors. DHT, but not testosterone, at 10(-7) M significantly increased 5 alpha R activity (rat, 1.5 +/- 0.3% to 3.0 +/- 0.4%; human, 7.6 +/- 1.7% to 11.4 +/- 2.9%; P < 0.01). IGF-I (10(-9)-6.4 x 10(-9) M), but not IGF-II (10(-9)-10(-8) M) or insulin (10(-9)-10(-7) M), increased enzyme activity in a dose-related fashion [i.e. 1.5 +/- 0.5 to 10 +/- 2 in rat and 6.0 +/- 1.1 to 9.8 +/- 1.6% (P < 0.01) in human cells]. No change in cell numbers was observed in any experiment. Since the effect of IGF-I was about 100 times that of androgen, we studied the possibility that androgen induction of the enzyme activity could be via IGF-I production. Addition of a monoclonal antibody against IGF-I significantly reduced the effect of DHT, and simultaneous addition of a specific IGF-I receptor antibody blocked the expected induction of 5 alpha R activity (control, 4.9 +/- 0.5; DHT, 8.0 +/- 1.9; DHT plus IGF-I receptor antibody, 3.7 +/- 0.4%). No effect on 3 alpha-reduction of [3H]DHT to 3 alpha-androstanediol was detected in separate experiments. These studies indicate that IGF-I may be an important regulator of skin 5 alpha R activity and, thus, may influence DHT formation. The previously known androgen induction of this peripheral steroidogenic enzyme may be via paracrine/autocrine production of an IGF-I-type growth factor.

Multifactorial regulation of IGF‐I gene expression

Insulin-like growth factor-I (IGF-I) is a highly conserved 70-residue circulating peptide with diverse biological effects. In mammals IGF-I is an essential mediator of normal postnatal growth and its expression is influenced by hormonal, nutritional, tissue-specific, and developmental factors. Recent studies have demonstrated that the IGF-I gene is more complicated than might have been predicted from its simple protein sequence. In rats and in humans the single-copy six-exon gene is transcribed by adjacent promoters into nascent RNAs with different 5' leader sequences that undergo both alternative RNA splicing and differential polyadenylation to yield multiple mature transcripts. These observations suggest that trophic agents may modulate expression of IGF-I at any of several nodal points. In this report we review several of the mechanisms responsible for regulating production of IGF-I in the rat. During neonatal development IGF-I gene transcription is progressively activated, leading to a rise in both hepatic IGF-I mRNA and in serum IGF-I. The induction of IGF-I expression is limited to mRNAs directed by promoter 1, the more 5' of two rat IGF-I gene promoters, and precedes the ontogenic appearance of liver growth hormone (GH) receptors, indicating that mechanisms independent of GH activate IGF-I expression during early postnatal life. By contrast, in adult GH-deficient rats, a single intraperitoneal injection of GH causes a prompt rise in IGF-I gene transcription that is mediated equivalently by promoters 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Gene regulation by IGF-I.

Constitutive overexpression of the insulin-like growth factor-I (IGF-I) receptor makes 3T3 cells capable of growing in serum-free medium supplemented solely with IGF-I to the total exclusion of the platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptors, the other two receptors that are required for the growth of 3T3 cells. Pietrzkowski et al. (Cell Growth Differ 92:199-205, 1992) found that these cells, overexpressing the IGF-I receptor, can also be induced to grow by the addition of EGF. We have ascertained that the mechanism by which EGF induces growth in these cells is through the induction of substantial amounts of IGF-I RNA and IGF-I. In 3T3 cells overexpressing the EGF receptor, a functional IGF-I receptor is still required for growth. We have also found, using a temperature-sensitive mutant of the SV40 large T antigen, that the levels of IGF-I mRNA and of IGF-I secreted in the medium are markedly increased by a functional T antigen. Using an IGF-I promoter driving a reporter luciferase gene, we have determined that this increase in the expression of IGF-I by T-antigen occurs, at least in part, at a transcriptional level. It seems, therefore, that transformation by SV40 reduces the requirement for growth factors by increasing the production of IGF-I.

T-type Ca2+ channels are required for adrenocorticotropin-stimulated cortisol production by bovine adrenal zona fasciculata cells.

The function of low voltage-activated T-type Ca2+ channels in ACTH-stimulated cortisol production by bovine adrenal zona fasciculata cells (AZF) was explored in patch clamp and secretion studies. Nearly all AZF cells expressed only a low voltage-activated T-type Ca2+ current (IT) that was blocked by the diphenylbutylpiperidine (DPBP) Ca2+ antagonists penfluridol and pimozide with IC50S of 0.3 and 0.5 microM, respectively. Dihydropyridine (DHP) Ca2+ antagonists, including nimodipine, nisoldipine, and felodipine, also blocked T-type Ca2+ current with IC50S ranging from 3.5-8.8 microM. Inhibition of IT by DPBP and DHP antagonists was voltage and use dependent. ACTH (1 nM) stimulated large (> 50-fold) increases in cortisol production by AZF cells, which were inhibited by Ca2+ antagonists at concentrations similar to those which blocked IT. Inhibition of cortisol production by Ca2+ antagonists was specific; ACTH-induced insulin-like growth factor-I production by AZF cells was not affected by DPBP antagonists. The L channel-specific DHP Ca2+ agonist (-)Bay K 8644 did not enhance basal or ACTH-stimulated cortisol synthesis. These results demonstrate that functional T-rather than L-type Ca2+ channels are required for ACTH-stimulated cortisol synthesis. They also suggest that these low voltage-activated channels, acting as the primary pathway for Ca2+ entry into AZF cells, couple ACTH-stimulated membrane depolarization to steroid hormone production.

In vivo and in vitro effect of growth hormone on estradiol secretion by human granulosa cells.

GH therapy increases the ovarian response to gonadotropin stimulation in women presenting with ovaries that are relatively resistant to conventional gonadotropin therapy. As it is not completely certain whether GH modulates the actions of FSH on granulosa cells directly or via insulin-like growth factor-I (IGF-I) production, we studied its effect on steroid release by human granulosa cells obtained from subjects affected by unexplained or male factor infertility. In all subjects, superovulation for in vitro fertilization/embryo transfer was induced by treatment with gonadotropins or GH plus gonadotropins combined. The effects of the different in vivo treatments were evaluated in the conditioned medium obtained after the first 24 h of incubation; granulosa cells from patients treated with GH released higher amounts of estradiol and progesterone into the medium than did granulosa cells from patients treated with gonadotropins alone. When the release of steroid due to the in vivo treatment was exhausted, cells were subjected to increasing concentrations of GH in the presence or absence of 200 nmol anti-IGF Sm 1.2 monoclonal antibody (MoAb) or the antitype I receptor alpha IR3 MoAb. The results revealed that GH stimulates estradiol production in a dose-dependent fashion, and the presence of the MoAbs drastically reduces the GH effect. These data demonstrate that the established stimulatory effect of GH on ovarian function is dependent not only on the increased levels of circulating IGF-I, but also on a direct effect of GH on granulosa cells, which seems to be mediated at least in part by the autocrine action of IGF, particularly IGF-II. In fact, chromatographic analysis of medium conditioned by human granulosa cells revealed that these cells clearly produce IGF-II and IGF-binding proteins and only small amounts of IGF-I. Since GH appears to be able to increase the in vitro effect of both IGF-I and IGF-II, we can hypothesize a sensitization of the granulosa cells to the IGF-II produced by the cells themselves, which acts through the IGF-I receptor.

Effects of insulin, insulin-like growth factor I, and gonadotropins on bovine granulosa cell proliferation, progesterone production, estradiol production, and(or) insulin-like growth factor I production in vitro1

The objectives of the present studies were to determine the effect of insulin, insulin-like growth factor I (IGF-I), testosterone, and FSH on proliferation, progesterone production, and(or) estradiol production of bovine granulosa cells. In addition, existence of IGF-I mRNA in granulosa cells and in vitro IGF-I production by granulosa cells were assessed. Cells from small (1 to 5 mm) and large (> or = 8 mm) follicles were collected from cattle and cultured for either 3 or 4 d. When cells from small follicles were cultured, insulin (.1 to 10 micrograms/mL) and IGF-I (100 to 400 ng/mL) increased (P < .05) cell numbers compared with controls. Insulin alone or IGF-I alone increased (P < .05) progesterone production per cell by severalfold on d 4. In cells from both sizes of follicles, insulin (1 microgram/mL), in the presence of FSH, increased estradiol production per cell. In contrast, IGF-I (100 ng/mL) inhibited estradiol production by cells from small follicles and stimulated estradiol production by cells from large follicles. Insulin-like growth factor II (100 ng/mL) and insulin at higher doses (> or = 5 micrograms/mL) had no effect on estradiol production by cells from small and large follicles. Granulosa cells contained four IGF-I mRNA transcripts and produced IGF-I in vitro. These results support the hypothesis that insulin and IGF-I may have direct local effects on bovine ovarian function, and that these effects are influenced by dose and size of follicle.

Secretion of insulin-like growth factors in milk and their effect on the neonate

Many hormones and growth factors appear in milk and colostrum. Interest and research concerning these factors has recently been revitalized to study their role in both mammary and neonatal development. Colostrum is rich in insulin-like growth factor-I (IGF-I), IGF-II and IGF binding proteins (IGFBPs). The appearance of IGFs in colostrum is specific and the pattern of appearance is similar to that of immunoglobulins. Blood concentrations of IGF-I are significantly altered by the cessation and initiation of lactation. Increasing blood IGF-I concentrations by somatotropin treatment results in increased mass appearance of IGF-I into colostrum during the prepartum period with only modest increases at parturition. Because local production of IGF-I is low and not epithelial in origin, and because blood flux has been demonstrated, it is likely that most colostrum IGF-I is of blood origin. Conversely, mammary tissue epithelial cells synthesize and secrete IGFBPs. Peak secretory IGF-I and IGFBP colostrum concentrations are 10–30-fold that of blood concentrations. Two possible mechanisms of appearance are described. Because of the occurrence of IGFs in colostrum, the dietary effects of IGF-I on the newborn were of interest. Both intestinal and systemic changes were hypothesized. Calves were fed dietary treatments of: (1) milk replacer (MR), (2) pooled colostrum for four feedings, followed by MR, and (3) MR supplemented with 750 ng/ml of recombinant human (rh) IGF-I for one week. The dietary treatments had no effect on circulating neonate IGFBP profiles, yet IGFBPs changed with neonate age. Blood insulin and prolactin concentrations, but not IGF-I were altered initially. A latent increase in blood IGF-I concentrations in IGF-I-fed animals appeared after 4 to 5 days of feeding. At slaughter, there was more growth in intestinal proximal regions in rhIGF-I-fedanimals than in the colostrum-fed controls. Thermodynamic analysis of the IGF type I and II receptors of intestinal mucosal microsomes indicated that IGF-I feeding up-regulated (increased binding capacity) the type I IGF receptor, whereas dietary colostrum down-regulated the type II IGF receptor. These data support the concept of a physiological effect of colostrum-borne IGFs on the neonate.

The early postnatal development of the murine mandibular condyle is regulated by endogenous insulin-like growth factor-I.

Skeletal growth during the early postnatal period is thought to be GH-independent, and is probably regulated by intrinsic growth factors. We studied the involvement of locally produced insulin like growth factor-I (IGF-I) in the growth of the neonatal mandibular condyle. Immunofluorescence studies revealed intense staining with antibodies to IGF-I in the mandibular condyle of 2-day-old ICR mice. We have also shown that these mandibular condyles contain specific high-affinity binding sites (Kd = 0.157 nmol/l) for IGF-I (427 fmol/mg). Autoradiographical studies of iodinated IGF-I revealed that the distribution of the receptors for IGF-I was parallel to that of IGF-I production, mainly in the younger zones of the condyle, namely the chondroprogenitor and the chondroblast cell layers. Immunoinhibition of IGF-I resulted in an almost complete inhibition (-91%) of thymidine incorporation into DNA, as well as in marked degenerative changes in the morphological appearance of the condyle. Our studies support the hypothesis that early postnatal growth is dependent on the paracrine activity of endogenous GH-independent IGF-I.

Ontogenic study of Expression of IGF-I and Gh-Receptor (GHR) mRNA in pig Liver and Skeletal Muscle.

Many of the effects of growth hormone are now thought to be mediated via the stimulation of insulin-like growth factor-I (IGF-I) production by many tissues, especially the liver, with this stimulation being dependent upon the presence of the GH-receptor (GHR). IGF-I gene expression occurs via alternative promoters giving rise to class 1 and 2 transcripts, of which class 2 is thought to be preferentially responsive to GH (Saunders, Dickson, Pell &amp; Gilmour, 1991).The effects of IGF-I include the stimulation of DNA synthesis (mitogenesis) and protein synthesis in most cell types, together with the differentiation of many cell types into mature tissue, including the differentiation of muscle cells into muscle fibres. Thus the GH/IGF-I axis has been found to play a major part in the control of animal growth. For this reason, we studied the age related changes in IGF-I and GHR mRNA expression in pig liver and skeletal muscle.

Polycystic ovaries in non-obese and obese patients: possible pathophysiological mechanism based on new interpretation of facts and findings

This study was designed to investigate the basic concentrations of different hormones in obese and non-obese patients with polycystic ovarian disease (PCOD). Eight women with PCOD, of whom four were obese with body mass index (BMI, kg/m2) of > 25 and four were non-obese with BMI < 25, volunteered to participate in this study. Serum samples were taken every 20 min over an 8 h period, starting at 2300 h, on day 5 of a spontaneous or gestagen-induced cycle. Basic insulin concentration was found to be significantly higher in the obese women compared with their non-obese counterparts (P < 0.0001). Serum concentrations of insulin-like growth factor binding protein (IGFBP-I) and sex hormone binding globulin (SHBG) were found to be significantly lower (P < 0.001 for both hormones) in the obese compared with the non-obese women. Serum concentrations of insulin-like growth factor I (IGF-I) did not differ between the two groups. The non-obese women had significantly higher serum concentrations of luteinizing hormone (LH) (P < 0.001) and of growth hormone (GH) (P < 0.002) than their obese counterparts. Based on these results, two models of the development of PCOD were suggested. In obese women, hyperinsulinaemia causes an excessive production of androgens through the enhancement of IGF-I receptors which, in synergism with LH, causes increased activity of cytochrome P-450c 17a. In non-obese patients, relative increase of GH concentration stimulates excessive ovarian IGF-I production. At this point synergism with LH results in excessive production of androgens by the same mechanism as in obese patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin‐like growth factor‐I (IGF‐I) production by astroglial cells: Regulation and importance for epidermal growth factor‐induced cell replication

The insulin-like growth factors are postulated to play a role during brain development. Because they are believed to act in a paracrine/autocrine manner, the production of insulin-like growth factor-I (IGF-I) by cultured astroglial cells was examined. Quantities of IGF-I in conditioned media were determined by RIA after separation of IGFs from IGF-binding proteins by high-pressure liquid chromatography. Astrocytes from 1-day-old rats and the rat glioma cell line (C6) both secreted 7.5-kDa IGF-I. A peak of immunoreactivity with an apparent mol wt of 12,000 was additionally present in media conditioned by C6 cells. Exposure to epidermal growth factor (EGF) increased media content of immunoreactive IGF-I slightly (60%) in C6 cells but more than 2-fold in normal astrocytes. Fibroblast growth factor also increased the amount of IGF-I contained in media conditioned by normal astrocytes. To determine whether the secreted IGF-I was biologically active, media IGFs were immunoneutralized with a monoclonal antibody (Sm 1.25). In the presence of the antibody, EGF-stimulated astrocyte replication was blocked. These data indicate that IGF-I secretion by rodent astrocytes is stimulated by factors thought to be important for brain growth and development and that the IGFs are likely intimate participants in EGF-induced astrocyte growth.

Human growth hormone and human aging

UNTIL recently, there has been little scientific inquiry into the physiological significance of, and possible therapy for, GH deficiency in adulthood. This was because the lack of efficacy in humans of animal-derived (e.g.1 bovine or porcine) GH and the limited supply of human cadaveric GH restricted use of exogenous GH to treatment of GHdeficient children. The availability of recombinant human GH (rhGH) has led to a renewal of scientific and clinical interest in investigating wider indications for GH administration. It is now recognized that GH deficiency may exert adverse metabolic effects in adults with panhypopituitarism, and that these effects can be reversed or attenuated by treatment with rhGH (1, 2). Recently, it has also become apparent that, with advancing age, an increasing proportion of men and women with no clinical evidence of pituitary pathology show decreases in GH secretion and serum levels of insulin-like growth factor-I (IGF-I) (3, 4). Because GH deficiency (1, 2) and normal aging (5) are both associated with decreases in protein synthesis and percent of lean body and bone mass, and with increases in percent of body fat, it is possible that reduced GH secretion and IGF-I levels might account, at least in part, for one or more of the above effects of aging, and that some older people might benefit from treatment with rhGH. In this regard, in several recent studies, administration of rhGH for periods varying from a few weeks to 6 months has resulted in improvements in nitrogen balance, an increase in lean body mass, and a decrease in percent body fat in older persons with low IGF-I levels (3, 4, 6, 7). We review herein the published work describing the alterations in GH and IGF-I production with increasing age, and the methods, benefits, and risks of GH treatment of older persons in the light of new knowledge regarding basic physiology of GH secretion and action. We also attempt to point out areas requiring further investigations.

Growth hormone (GH) and adult bone remodeling: the potential use of GH in treatment of osteoporosis.

Decreased osteoblastic activity seems to be of major importance in the pathogenesis of postmenopausal and senile osteoporosis and several lines of evidence suggest that GH may become useful in treatment of osteoporosis. GH stimulates osteoblastic proliferation and differentiation in vitro and increases production of Insulin-like Growth Factor-I and II (IGF-I and IGF-II) which both have profound stimulatory effects on osteoblasts and are important local regulators of bone remodeling. GH affects several other osteotropic hormones in vivo and increases bone turnover while the effect on bone mass is less pronounced and depends on the skeletal compartment. The few published clinical studies on the use of GH in treatment of osteoporosis have been inconclusive and well controlled studies of adequate size are greatly needed. Future research should focus on intermittent use of GH in combination with other hormones stimulating IGF production or antiresorptive agents.

Prostaglandins: Mechanisms of action and regulation of production in bone

Prostaglandins (PGs), particularly PGE2, are produced by bone and have powerful effects on bone metabolism. PGs have an initial, transient, direct inhibitory effect on osteoclast function. However, the major long-term effect in bone organ culture is to stimulate bone resorption by increasing the replication and differentiation of new osteoclasts. PGs also stimulate osteoclast formation in cell culture systems. Stimulation of osteoclastic bone resorption may be important in mediating bone loss in response to mechanical forces and inflammation. PGs have a biphasic effect on bone formation. At relatively low concentrations or in the presence of glucocorticoids, the replication and differentiation of osteoblasts is stimulated and bone formation is increased. This increase is associated with an increase in production of insulin-like growth factor-I (IGF-I). However, at high concentrations or in the presence of IGF-I, PGE2 inhibits collagen synthesis. In osteoblastic cell lines this inhibition can be shown to occur at the level of transcription of the collagen gene. The stimulatory effect on bone formation has been demonstrated when PGs are administered exogenously, but it is not clear how endogenous PG production affects bone formation in physiological or pathologic circumstances. The production of PGs in bone is highly regulated. The major source appears to be cells of the osteoblast lineage. A major site of regulation is at the level of the enzyme PG endoperoxide synthase (cyclooxygenase or PGH synthase). PGE2 production and PGH synthase mRNA are increased by PTH and interleukin-1 and decreased by estrogen. Glucocorticoids probably act by a different mechanism, decreasing either arachidonic acid or PGH synthase activity.(ABSTRACT TRUNCATED AT 250 WORDS)