Androgens promote insulin-like growth factor-I and insulin-like growth factor-I receptor gene expression in the primate ovary.

It has recently been shown that androgens increase the growth of immature follicles in the primate ovary. In the present study the effect of androgens on ovarian insulin-like growth factor I (IGF-I) and IGF-I receptor gene expression was investigated. The study groups included five follicular phase, placebo-treated controls, and four testosterone- and three dihydrotestosterone (DHT)-treated rhesus monkeys. The treatment period was 5 days. Both testosterone and DHT treatment resulted in significant, 3-4-fold increases in IGF-I mRNA concentration in granulosa, thecal and interstitial compartments. Likewise, both androgens induced significant increases in the amount of IGF-I receptor mRNA, most notably in thecal cells and less markedly in granulosa and interstitium (P < 0.05). These changes in amounts of IGF system mRNA were documented in growing follicles up to the small antral (相似文献   

Central administration of insulin-like growth factor-I decreases depressive-like behavior and brain cytokine expression in mice

Exogenous administration of insulin-like growth factor (IGF)-I has anti-depressant properties in rodent models of depression. However, nothing is known about the anti-depressant properties of IGF-I during inflammation, nor have mechanisms by which IGF-I alters behavior following activation of the innate immune system been clarified. We hypothesized that central IGF-I would diminish depressive-like behavior on a background of an inflammatory response and that it would do so by inducing expression of the brain-derived neurotrophic factor (BDNF) while decreasing pro-inflammatory cytokine expression in the brain. IGF-I (1,000 ng) was administered intracerebroventricularly (i.c.v.) to CD-1 mice. Mice were subsequently given lipopolysaccharide i.c.v. (LPS, 10 ng). Sickness and depressive-like behaviors were assessed followed by analysis of brain steady state mRNA expression. Central LPS elicited typical transient signs of sickness of mice, including body weight loss, reduced feed intake and decreased social exploration toward a novel juvenile. Similarly, LPS increased time of immobility in the tail suspension test (TST). Pretreatment with IGF-I or antidepressants significantly decreased duration of immobility in the TST in both the absence and presence of LPS. To elucidate the mechanisms underlying the anti-depressant action of IGF-I, we quantified steady-state mRNA expression of inflammatory mediators in whole brain using real-time RT-PCR. LPS increased, whereas IGF-I decreased, expression of inflammatory markers interleukin-1ß (IL-1ß), tumor necrosis factor-(TNF)α, inducible nitric oxide synthase (iNOS) and glial fibrillary acidic protein (GFAP). Moreover, IGF-I increased expression of BDNF. These results indicate that IGF-I down regulates glial activation and induces expression of an endogenous growth factor that shares anti-depressant activity. These actions of IGF-I parallel its ability to diminish depressive-like behavior.     

Antiproliferative effects and insulin-like growth factor-I expression in Balb-C 3T3 fibroblasts after treatment with somatostatin and gonadotropin-releasing hormone analogs

The present study was aimed to compare antiproliferative effects of somatostatin (SS) and gonadotropin-releasing hormone analogs (GnRHa) on a fibroblast cell line. Proliferation index, cell count, viability of the cells and insulin-like growth factor-I (IGF-I) immunoreactivity were determined after treatment with either SS (100 microM/ml), GnRHa (35 nM/ml) or SS and GnRHa of Balb-C 3T3 mouse fibroblasts. It was found that the proliferation index, cell count, viability and IGF-I immunoreactivity were not affected by GnRHa treatment as compared with no treatment (p > 0.05). Application of SS to the fibroblasts resulted in a significant reduction in proliferation index, cell count, and IGF-I immunoreactivity as compared with GnRHa treatment and no treatment, but it had no effect on cell viability. The labelling index in SS-treated cells was significantly reduced as compared with combined treatment with SS and GnRHa. In conclusion, a direct effect of GnRHa on fibroblast cells in culture could not be demonstrated. SS had direct inhibitory effects on cell proliferation possibly via inhibition of IGF-I effects without affecting cell viability.     

Control of growth hormone receptor and insulin-like growth factor-I expression by cortisol in ovine fetal skeletal muscle

Insulin-like growth factor (IGF)-I has an important role in myogenesis but its developmental regulation in skeletal muscle before birth remains unknown. In other tissues, cortisol modulates IGF gene expression and is responsible for many of the prepartum maturational changes essential for neonatal survival. Hence, using RNase protection assays and ovine riboprobes, expression of the IGF-I and growth hormone receptor (GHR) genes was examined in ovine skeletal muscle during late gestation and after experimental manipulation of fetal plasma cortisol levels by fetal adrenalectomy and exogenous cortisol infusion. Muscle IGF-I, but not GHR, mRNA abundance decreased with increasing gestational age in parallel with the prepartum rise in plasma cortisol. Abolition of this cortisol surge by fetal adrenalectomy prevented the prepartum fall in muscle IGF-I mRNA abundance. Conversely, raising cortisol levels by exogenous infusion earlier in gestation prematurely lowered muscle IGF-I mRNA abundance but had no effect on GHR mRNA. When all data were combined, plasma cortisol and muscle IGF-I mRNA abundance were inversely correlated in individual fetuses. Cortisol is, therefore, a developmental regulator of IGF-I gene expression and is responsible for suppressing expression of this gene in ovine skeletal muscle near term. These observations have important implications for muscle development both before and after birth, particularly during conditions which alter intrauterine cortisol exposure.     

The regulation of L-proline transport by insulin-like growth factor-I in human osteoblast-like SaOS-2 cells

The effect of insulin-like growth factor-I on amino acid transport was studied by measuring the uptake of tritiated L-proline in the cultured human osteoblast-like SaOS-2 cells. The uptake of L-proline was supported by both transport system A, ASC and Gly and by Na⁺-dependent amino acid transport system A, and by Na⁺-independent system L. The initial rate of total L-proline uptake as a function of concentration showed saturation and obeyed Michaelis-Menten kinetics with Michaelis constant (K _m) and maximum velocity (V _max) values of 1.87 mM and 8.89 nmol⋅(mg protein)⁻¹⋅(3 min)⁻¹, respectively. Na⁺-dependent L-proline uptake was significantly stimulated by insulin-like growth factor-I in a time- and concentration-dependent manner. Kinetic analysis showed that insulin-like growth factor-I enhanced transport activity by increasing the V _max of transport without significant changes in the affinity (K _m) of the carrier for the substrate. The increase in transport activity was significantly reduced by cycloheximide. The stimulated increment above basal L-proline uptake was completely inhibited by α-(methylamino) isobutyric acid, suggesting that only system A was affected by insulin-like growth factor-I. Na⁺-dependent L-proline uptake was also stimulated by insulin-like growth factor-II and insulin-like growth factor-I analogues. The insulin-like growth factor-I-stimulated L-proline uptake was inhibited by one of its binding protein, insulin-like growth factor binding protein-4, in a concentration-dependent manner. Received: 15 January 1996/Accepted 21 February 1996     

Intracerebroventricular infusion of insulin-like growth factor-I ameliorates the age-related decline in hippocampal neurogenesis.

The dentate gyrus of the hippocampus is one of few regions in the adult mammalian brain characterized by ongoing neurogenesis. Significantly, recent studies indicate that the rate of neurogenesis in the hippocampus declines with age, perhaps contributing to age-related cognitive changes. Although a variety of factors may influence the addition of new neurons in the adult dentate gyrus, the mechanisms responsible for the age-related reduction remain to be established. Insulin-like growth factor-I (IGF-I) is one promising candidate to regulate neurogenesis in the adult and aging brain since it influences neuronal production during development and since, like the rate of neurogenesis, it decreases with age. In the current study, we used bromodeoxyuridine labeling and multilabel immunofluorescence to assess age-related changes in neuronal production in the dentate gyrus of adult Brown Norway x Fischer 344 rats. In addition, we investigated the relationship between changes in neurogenesis and the age-dependent reduction in IGF-I by evaluating the effect of i.c.v. infusion of IGF-I on neurogenesis in the senescent dentate gyrus. The analyses revealed an age-dependent reduction in the number of newly generated cells in the adult dentate subgranular proliferative zone and, in addition, a 60% reduction in the differentiation of newborn cells into neurons. Restoration of IGF-I levels in senescent rats significantly restored neurogenesis through an approximately three-fold increase in neuronal production.The results of this study suggest that IGF-I may be an important regulator of neurogenesis in the adult and aging hippocampus and that an age-related decline in IGF-I-dependent neurogenesis could contribute to age-related cognitive changes.     

Effect of insulin-like growth factor-I gene therapy on the somatotropic axis in experimental prolactinomas

Insulin-like growth factor-I (IGF-I) provides a physiologic feedback effect within the somatotropic axis. Gene therapy was implemented in young female Sprague-Dawley rats which received 2 pituitary stereotaxic injections of a control recombinant adenoviral vector expressing green fluorescent protein (RAd-GFP) or IGF-I (RAd-IGF-I). The animals were sacrificed 7 days after injection. Previously, on day -23, the experimental groups received subcutaneous implants of 17-beta estradiol. Morphometric analysis revealed that the somatotrope cells in estrogen-treated rats without stereotaxic injections showed a significant (p < 0.01) increase in the cell size compared with intact controls (59.9 +/- 1.1 vs. 42.9 +/- 1.2 microm(2)) and had a significant (p < 0.05) decrease in cell density with respect to intact animals (10.5 +/- 0.1 vs. 19.7 +/- 1.7). The treatment of pituitary adenomas with RAd-IGF-I induced a significant (p < 0.05) decrease in cell size with respect to E(2) + RAd-GFP (51.3 +/- 0.3 vs. 58.9 +/- 0.3 microm(2)) and no changes in cell density compared with RAd-GFP-injected animals (12.8 +/- 1.7 vs. 10.5 +/- 0.1). Serum growth hormone was higher (p < 0.01) in estrogen-treated animals versus controls (146.7 +/- 6 vs. 73.9 +/- 9 ng/ml). In rats carrying estrogen-induced adenomas, RAd-IGF-I injection induced a significant (p < 0.05) decrease in serum growth hormone compared to RAd-GFP-injected animals (107.5 +/- 7 vs. 142.4 +/- 9 ng/ml). IGF-I gene therapy appears to be an effective approach for the treatment of experimental somatomammotropic pituitary tumors and could be potentially useful as an adjuvant of conventional therapies.     

The regulation of type-I collagen synthesis by insulin-like growth factor-I in human osteoblast-like SaOS-2 cells

 The effect of insulin-like growth factor-I on collagen synthesis was studied using cultured human osteoblast-like SaOS-2 cells by measuring the incorporation of tritiated L-proline into immunoprecipitable type-I collagen. Tritiated L-proline incorporation into collagen was significantly stimulated by insulin-like growth factor-I in a time- and concentration-dependent manner. Unlabelled L-proline and α-(methylamino) isobutyric acid inhibited either the influx into cells, or the incorporation into collagen, of tritiated L-proline. The increase in incorporation of tritiated L-proline was significantly reduced by cycloheximide and actinomycin D. L-Proline incorporation into collagen was also stimulated by insulin-like growth factor-II, insulin-like growth factor-I analogues and insulin. The insulin-like growth factor-I-stimulated L-proline incorporation was inhibited by one of its binding proteins, insulin-like growth factor binding protein-4, in a concentration-dependent manner. Received: 24 July 1996 / Received after revision and accepted: 11 September 1996     

Stimulatory effect of zinc and growth factor on bone protein component in newborn rats: enhancement with zinc and insulin-like growth factor-I

The effect of zinc and growth factor on bone protein component in newborn rats was investigated. The characterization of protein component in the femoral-diaphyseal and metaphyseal tissue of newborn rats (3-35 days old) was examined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The diaphyseal and metaphyseal tissues of 7 days-old rats were cultured for 24 or 48 h in a medium containing either vehicle, zinc sulfate (10-4 M) or dipicolinate (10-3 M), a chelator of zinc ion, in the presence or absence of insulin-like growth factor-I (IGF-I; 10-8 M) or transforming growth factor-beta (TFG-beta; 10-10 M) with an effective concentration. Many cellular protein molecules were present in the diaphyseal and metaphyseal tissues; potent bands were seen in protein molecules with about 66 and 46 kDa. Protein molecule of about 66 kDa was greatly released in the medium cultured with the diaphyseal and metaphyseal tissues. This protein in the medium was increased by culture with zinc, IGF-I or TGF-beta. Total protein content in the medium cultured with the diaphyseal and metaphyseal tissues was significantly increased in the presence of zinc, IGF-I or TGF-beta. The IGF-I-increased medium protein content was significantly enhanced by zinc. This enhancing effect was not seen in TGF-beta. Alkaline phosphatase activity and deoxyribonucleic acid (DNA) content in the diaphyseal and metaphyseal tissues was significantly increased by culture with zinc, IGF-I or TGF-beta. The effect of IGF-I was significantly enhanced by zinc, while it was not found in TGF-beta. The effect of IGF-I or TGF-beta in increasing the bone components was seen in the presence of dipicolinate. This study demonstrates that zinc, like IGF-I and TGF-beta, can increase protein components in the femoral-diaphyseal and metaphyseal tissues of new-born rats. Zinc may especially play a role in bone growth in collaboration with IGF-I.     

Delivery of insulin-like growth factor-I to the rat brain and spinal cord along olfactory and trigeminal pathways following intranasal administration

We investigated the CNS delivery of insulin-like growth factor-I (IGF-I), a 7.65 kDa protein neurotrophic factor, following intranasal administration and the possible pathways and mechanisms underlying transport from the nasal passages to the CNS. Anesthetized adult male Sprague-Dawley rats were given [125I]-IGF-I intranasally or intravenously and then killed by perfusion-fixation within 30 min. Other animals were killed following cisternal puncture and withdrawal of cerebrospinal fluid (CSF) or intranasal administration of unlabeled IGF-I or vehicle. Both gamma counting of microdissected tissue and high resolution phosphor imaging of tissue sections showed that the tissue concentrations and distribution following intranasal administration were consistent with two routes of rapid entry into the CNS: one associated with the peripheral olfactory system connecting the nasal passages with the olfactory bulbs and rostral brain regions (e.g. anterior olfactory nucleus and frontal cortex) and the other associated with the peripheral trigeminal system connecting the nasal passages with brainstem and spinal cord regions. Intranasal administration of [125I]-IGF-I also targeted the deep cervical lymph nodes, consistent with their possible role in lymphatic drainage of both the nasal passages and the CNS. Cisternal CSF did not contain [125I]-IGF-I following intranasal administration. Intravenous [125I]-IGF-I resulted in blood and peripheral tissue exposure similar to that seen following intranasal administration but CNS concentrations were significantly lower. Finally, delivery of IGF-I into the CNS activated IGF-I signaling pathways, confirming some portion of the IGF-I that reached CNS target sites was functionally intact. The results suggest intranasally delivered IGF-I can bypass the blood-brain barrier via olfactory- and trigeminal-associated extracellular pathways to rapidly elicit biological effects at multiple sites within the brain and spinal cord.     

Growth hormone, insulin-like growth factor-1, and the insulin-like growth factor binding proteins in rats maintaining reduced body protein following lesions of the lateral hypothalamus

Rats with lesions of the lateral hypothalamus (LH) maintain a reduced body protein mass that they effectively defend when challenged by under- or over-nutrition. The two studies reported here evaluate the potential contributions of growth hormone (GH), insulin-like growth factor-1 (IGF-1), and the insulin-like growth factor-binding (IGFBP) to this persistent maintenance of a reduced body protein mass by LH rats. At 18 weeks postlesion, it was found that the serum levels of GH, IGF-1, total IGFBP, and IGFBP-3 of LH rats maintaining reduced body protein were not different from those of age-matched controls. However, closer to the time of surgery, at which time the lesion-induced body protein adjustments are known to occur, altered hormone and binding protein levels were observed. Specifically, at 3 weeks after lesioning, the IGF-binding proteins of LH rats were significantly elevated, whereas their GH levels were lower than those of controls. Because the GH, IGF-1, and IGF-binding proteins of LH rats were comparable to those of controls at 18 weeks after lesioning, none apparently underlie the chronically reduced body protein mass that LH rats display. Closer to the time of lesioning, however, altered GH and IGF binding protein levels may contribute to the postlesion adjustments by which the body protein mass of LH rats is lowered to its reduced level.     

Exogenous steroids and the control of oestradiol secretion by human granulosa-lutein cells by follicle stimulating hormone and insulin-like growth factor-I

This study first examined the relative activities of 17-hydroxylase,17, 20-lyase and aromatase in human granulosa–lutein cellsby challenging the cells with steroid precursors in the oestradiolbiosynthetic pathway. When cells from four patients were challengedwith precursor steroids on the pathway to oestrogen synthesis(pregnenolone, 17-hydroxypregnenolone, progesterone, 17-hydroxyprogesteroneand androstenedione at 5 x 10^–6 M), oestradiol (nmol/l)outputs after 1 day of culture were (median, interquartile range)as follows: 4.1 (2.1– 8.8; pregnenolone), 3.1 (1.7–6.0;progesterone), 12.5 (6.9–18.1; 17hydroxypregnenolone),8.2 (4.1–16.7; 17hydroxyprogesterone) and 251 (140–819;androstenedione). No further increases were seen when the steroidconcentration was increased to 1 x 10^–5 M. Basal oestradiolsecretion was 3.5 (1.6–8.2) nmol/l. We conclude that theconversion of pregnenolone/progesterone to oestradiol by granulosa–luteincells is rate limited by 17-hydroxylase activity but that thesecells are capable of oestradiol secretion (in the nmol/l range)in the absence of androstenedione. In the second part of thisstudy we examined the control of granulosa–lutein oestradiolsecretion by follicle stimulating hormone (FSH) and insulinlikegrowth factor-I (IGF-I) in the presence and absence of exogenousandrostenedione (10^–6 M). Cells were cultured for up to6 days and basal oestradiol (nmol/l) fell dramatically overthis period both in the presence and absence of androstenedione,e.g. from 339 (223–419) (median and interquartile range,cells from five patients cultured in the presence of androstenedione)after 2 days to 14 (7–59) after 6 days. There was no effectof FSH (83/575, 0–160 IU/l) in the absence of androstenedionebut in its presence FSH (96 IU/l) increased oestradiol secretionslightly by 153 ±45 (day 4) and 151 ± 21 (day6; results mean ± SEM, percentage increase over time-matchedcontrols; cells from five patients). In contrast, the effectof IGF-I (30 ng/ml) was to markedly enhance oestradiol secretionto 1099±320% (n = 7) of the control (day 4) in the absenceof exogenous androgen and to 551 ± 184% (n = 5) in itspresence. There was no evidence of any synergistic interactionbetween IGF-I and FSH during the culture period in the absenceof androstenedione. However, there was a synergistic effectfor IGF-I (30 ng/ml)/FSH (96 IU/l) after 6 days in culture inits presence in that oestradiol secretion increased by 1748± 294% (n = 5) compared to 157 ± 21% (FSH) and1211 ± 233% (IGF-I) for the stimulators on their own.However, this effect may be explained, in part, by the increasein cell number provoked by IGF-I over this culture period. Weconclude that (i) under these conditions granulosa cells showedlow 17-hydroxylase activities, (ii) granulosa cells are capableof synthesizing oestradiol in the absence of exogenous androgens,the substrates for the aromatase complex, and (iii) FSH is oflittle importance in stimulating oestradiol secretion from granulosa-luteincells, and the evidence for it positively modulating IGF-I activityis poor.     

Reversal of desipramine-induced suppression of paradoxical sleep by a long-acting somatostatin analogue (octreotide) in rats

EEG sleep recordings were performed in rats under intraperitoneal injections of saline, desipramine (DMI, 4 mg/kg) an inhibitor of noradrenaline reuptake, and DMI plus the octapeptide somatostatin analogue (octreotide, 0.2 mg/kg). As already reported, DMI resulted in selective suppression of paradoxical sleep (PS) and increased slow wave sleep (SWS). The administration of the octapeptide somatostatin analogue totally reversed the DMI-induced suppression of PS, but had no effect on SWS. This finding confirms previous results demonstrating a role of somatostatin in the generation of PS. In addition, it suggests that the suppression of PS by DMI may be due to an inhibitory effect on somatostatin release, rather than to an alteration of brain noradrenaline.     

Prenatal expression of growth hormone receptor/binding protein and insulin-like growth factor-I (IGF-I) in the enamel organ

Immunohistochemistry was used to study the ontogeny of GH receptor/binding protein (GHR/BP) and IGF-I from the 13-day-old embryo (E13) to the E19 rat fetus in the developing incisor and molar. Analysis of serial sections revealed diffuse staining of GHR/BP and IGF-I at the bud and early cap stages within both the mesenchyme of the dental papilla and the ectodermal-erived enamel organ. Just before transition to the cap stage, immunoreactivity of GHR/BP and IGF-I increased in the epithelial bud and extended to the condensed dental mesenchyme. At the cap stage, the dental epithelium showed an intense expression of GHR/BP and IGF-I, whereas the dental mesenchymal cells showed very weak staining. The inner enamel epithelium and the outer enamel epithelium were positive for both GHR/BP and IGF-I in the bell stage. Differentiating ameloblasts, odontoblasts and the secretory ameloblasts and odontoblasts continued to express GHR/BP and IGF-I in incisors. These findings support the premise that growth hormone and IGF-I may play a role in embryonic tooth development by regulating the epithelial-mesenchymal interactions that influence events in growth and cytodifferentiation.     

Involvement of protein kinase C and nitric oxide in the modulation by insulin-like growth factor-I of glutamate-induced GABA release in the cerebellum

Insulin-like growth factor-I elicits a long-term depression of the glutamate-induced GABA release in the adult rat cerebellum that lasts at least several hours. We studied whether protein kinase C and nitric oxide may be involved in this effect of insulin-like growth factor-I on GABA release since both signalling pathways have been implicated in other forms of neuromodulation in the cerebellum. By using microdialysis in the adult rat cerebellum, we found that either an inhibitor of protein kinase C (staurosporine) or of nitric oxide synthase (Nw-nitro-l-arginine methyl ester) counteracted the long-term, but not the acute effects of insulin-like growth factor-I on glutamate-induced GABA release. On the contrary, when either an activator of protein kinase C (phorbol ester), or an nitric oxide donor (l-arginine), were given with glutamate, they mimicked only the acute effects of insulin-like growth factor-I on glutamate-induced GABA release. Finally, when both protein kinase C and nitric oxide-synthase were simultaneously inhibited by conjoint administration of staurosporine and Nw-nitro-l-arginine methyl ester, a complete blockage of both the short and the long-term effects of insulin-like growth factor-I on GABA release was obtained. These results, indicate that: (i) activation by insulin-like growth factor-I of either the protein kinase C or nitric oxide-signalling pathways is sufficient for the short-term inhibition of glutamate-induced GABA release; and (ii) simultaneous activation of both the protein kinase C and the nitric oxide signalling pathways is necessary for insulin-like growth factor-I to induce a long-term depression of GABA responses to glutamate.

Thus, long-term depression of glutamate-induced GABA release by insulin-like growth factor-I in the cerebellum is mediated by simultaneous activation of both protein kinase C and nitric oxide-signalling pathways.