Effect of hypophysectomy and growth hormone replacement on hypothalamic GHRH

Long-term (7 and 14 days) hypophysectomy resulted in a striking decrease in growth hormone releasing hormone-like immunoreactivity (GHRH-LI) in the median eminence (ME) of adult male rats, evaluated by both radioimmunoassay and immunohistochemistry. Treatment with human GH (125 μg/rat, twice daily IP for 14 days) prevented, though partially, depletion of GHRH-LI from the ME, as assessed by both methods. These results demonstrate that circulating GH levels regulate the function of GHRH-producing structures, via a feedback mechanism.     

Involvement of hypothalamic somatostatin in glucagon-induced suppression of growth hormone secretion in conscious rats

The role of central glucagon in regulating GH secretion was studied in conscious male rats with chronic indwelling intra-atrial and intracerebro-ventricular (ICV) cannulae. Repeated blood sampling every 20 min from 1000 hr to 1700 hr showed two major GH bursts occurring at regular intervals (3.6±0.1 hr) around 1200 hr and 1540 hr. The ICV (lateral ventricle) injection of glucagon (10 μg/rat) at 1100 hr inhibited spontaneous GH secretion, and the mean (±SE) plasma GH levels from 1120 hr to 1700 hr were lower than those in controls injected ICV with the vehicle solution only (31.9±7.8 ng/ml vs. 157.1±13.4 ng/ml, p<0.01). The GH bursts did not appear until 5 hr after the injection. The intravenous (IV) injection of glucagon (10 μg/rat) did not change plasma GH levels or the occurrence of spontaneous GH bursts. The glucagon-induced suppression of GH release was attenuated when anti-somatostatin serum (ASS), but not normal rabbit serum (NRS), was given IV in a volume of 0.25 ml immediately before the ICV injection of glucagon (10 μg/rat) (mean GH levels at 1120–1700 hr: ASS+glucagon, 133.6±26.7 ng/ml vs. NRS+glucagon, 30.5±7.4 ng/ml, p<0.01). These findings suggest that central glucagon may play an inhibitory role in regulating GH secretion by stimulating SRIF release from the hypothalamus in the rat.     

Inhibition of rat C6 glioblastoma tumor growth by expression of insulin-like growth factor I receptor antisense mRNA

 The expression of insulin-like growth factor I receptor (IGF-IR) antisense mRNA inhibits the growth of C6 rat glioblastoma cells both in vitro and in vivo [Cancer Res (1994) 54: 2218]. Moreover, the injection of C6 cells expressing an antisense mRNA to the IGF-IR into syngeneic rats prevents subsequent wild-type tumorigenesis and induces regression of established tumors. For the study of immune function in syngeneic rats, C6 cells expressing either IGF-IR sense or IGF-IR antisense mRNA were injected and splenic lymphocyte function analyzed in vitro after 2 weeks. Cytotoxic, CD8⁺ lymphocytes from animals injected with IGF-IR antisense cells, but not from those treated with IGF-IR sense cells, proliferated in vitro in response to wild-type C6 cells. Wild-type C6 cells or IGF-IR-sense-RNA-expressing cells rapidly formed tumors upon subcutaneous injection into athymic nude mice. IGF-IR antisense cells were weakly tumorigenic, exhibiting a six- to tenfold increase in tumor latency. Injection of IGF-IR antisense C6 cells mildly delayed the development of wild-type tumors, and did not induce the regression of established wild-type C6 tumors in athymic nude mice. Thus, these findings demonstrate the stimulation of a cellular immune response in rats following the injection of IGF-IR antisense cells. However, studies of athymic nude mice indicate that expression of IGF-IR antisense mRNA also inhibits C6 cells tumorigenicity by additional mechanisms. Received: 27 January 1995 / Accepted: 15 November 1995     

Growth hormone and insulin-like growth factor I concentrations in bulls of various growth hormone genotypes

A leucine/valine substitution at amino acid position 127 was identified by the polymerase chain reaction and restriction fragment length polymorphism in the bovine growth hormone gene. Genotyping was performed in 84 AI bulls of three different breeds, in which plasma concentrations of growth hormone (GH) and insulin-like growth factor I (IGF-1) were also measured. Gene frequencies of variants L (leucine) und V (valine) were 0.80/0.20 (Black and White), 0.90/0.10 (Brown), 0.71/0.29 (Simmental). Hormone concentrations were measured during different physiological conditions (normal feeding, fasting, realimentation) in the majority of animals. Generally, genotype LL was associated with higher concentrations of GH than LV. This difference was significant in Black and White bulls (P < 0.05). In contrast, IGF-1 concentrations were higher in LV than in LL animals. This was most pronounced in mature, realimented Simmental bulls. We conclude that the various GH alleles influence the circulating concentrations of GH and IGF-1.     

Effect of hypophysectomy on immunocytochemically demonstrated growth hormone releasing factor (GHRF) in the rat brain

The effect of removal of CH by long-term hypophysectomy (HPX) on the GHRF-immunoreactivity in the rat hypothalamus was studied using immunocytochemical methods. HPX resulted in a dramatic reduction in immunostaining in the median eminence (ME), indicating a significant reduction in storage of GHRF. Other regions of the hypothalamus, including the dorsomedial nucleus, the medial preoptic and suprachiasmatic regions, and the lateral hypothalamus showed the distribution and intensity of GHRF-immunoreactive structures as seen in intact animals; i.e., scattered fibers only. A few weakly stained cell bodies were seen in experimental and control animals. This could be due to a lack of storage, and/or this peptide may possibly not be present in its matured and fully immunoreactive form in the cell bodies.     

SRIF及CSH对斜带石斑鱼脑垂体生长激素合成和分泌的调控

斜带石斑鱼 (Epinepheluscoioides)属于雌性先成熟、具有性转变的雌雄同体鱼类。生长激素释放抑制因子 (SRIF)是鱼类生长激素 (GH)分泌的主要抑制性调节剂 ,半胱胺 (CSH)可抑制SRIF的作用。本文采用静态孵育系统 ,应用RPA及RIA研究SRIF及CSH对斜带石斑鱼GHmRNA表达及GH分泌的调节。结果显示 ,SRIF能以剂量依存方式抑制斜带石斑鱼脑垂体释放GH ,时间越长作用越强。但SRIF作用 2 4h对GHmR NA水平的影响不显著 ,表明SRIF是斜带石斑鱼GH释放的抑制性调节剂 ,对GHmRNA的表达没有明显影响。较低剂量的CSH (10 -4- 10 -2 mol/L)使斜带石斑鱼的GH释放量增加 ,较高剂量 (10 -1mol/L)的CSH引起的GH增加趋势减缓 ,这种现象可能与较高剂量的CSH不仅抑制下丘脑SRIF的释放 ,同时影响GHRH的释放 ,使得GH的分泌量增幅下降有关 ;无论是较高剂量还是较低剂量的CSH都不能使GHmRNA的水平增加 ,表明CSH只能引起GH的释放量增加 ,不影响GH的合成。GnRH与CSH共同作用引起的GH释放量明显高于CSH单独作用的效应 ,其主要原因是由于GnRH促进GHmRNA的表达所致     

Effect of recombinant growth hormone on expression of growth hormone receptor,insulin-like growth factor mRNA and serum level of leptin in growing pigs

Sixteen Large White × Landrace castrated male pigs were allotted into treatment and control group. The treatment group was injected intramuscularly with recombinant porcine growth hormone (rpGH, 4 mg d⁻¹) and the control group with vehicle for 28 days. Animals were slaughtered 4 h after final injection for liver, longissimus dorsi (LD) muscle and blood sampling. Serum concentration of insulin-like growth factor 1 (IGF-I) and leptin were determined by RIA. The total RNA was extracted from tissues to measure the abundance of growth hormone receptor (GHR), IGF-I mRNA by RT-PCR with 18S rRNA internal standard. Results showed that rpGH enhanced the average daily weight gain by 26.1% (P < 0.05), the serum IGF-I concentration by 70.94% (P < 0.01), decreased serum leptin by 34.8% (P < 0.01). The relative abundance of GHR and IGF-I mRNA in liver were increased by 24.45% (P < 0.05) and 45.30% (P < 0.01), respectively, but no difference of GHR (P > 0.05) and IGF-I mRNA (P > 0.05) in LD between GH treated and control group was found. These results suggest that rpGH can up-regulate hepatic GHR and IGF-I gene expression and improve animal growth. However the effect of rpGH on GHR and IGF-I gene expression are tissue-specific.     

Effect of recombinant growth hormone on expression of growth hormone receptor, insulin-like growth factor mRNA and serum level of leptin in growing pigs

Growth hormone (GH) plays an important role in regulation of animal growth, metabolism and lactation[1]. Numerous studies have shown that exogenous somatotropin (ST) can increase average daily weight gain, improve feed efficiency, stimulate protein deposition and muscle growth and decrease lipid accretion rate[1]. The original somatomedin hypothesis suggested that the effect of GH on postnatal growth was mediated by insulin-like growth hormone factor 1 (IGF-I) which was thought to be deriv…     

Cell kinetics of the growth plate in hypophysectomized rats treated with growth hormone and thyroxine

Summary The cell production in the growth plate of the proximal tibia was calculated in hypophysectomized rats given growth hormone and/or thyroxine from values of longitudinal bone growth determined with oxytetracycline and the size of degenerative cells in the growth plate.The changes in longitudinal bone growth induced by thyroxine and growth hormone in hypophysectomized rats were found to be predominantly caused by changes in the cell production, whereas the changes in the size of the degenerative cells were minor. The stimulation of cell production by growth hormone was dependent on the dose and the administration period. Thyroxine was found to stimulate the cell production up to an optimum dose of thyroxine.     

Immunohistochemical localization of insulin-like growth factor 1 and 2 in the endocrine pancreas of rat,dog, and man,and their coexistence with classical islet hormones

Immunohistochemical techniques were used to study the occurrence and distribution of insulin-like growth factor 1 (IGF-1) and IGF-2 in the pancreas of man, dog, and rat and their possible coexistence with insulin (INS), glucagon (GLUC), somatostatin (SOM) and pancreatic polypeptide (PP). All control experiments, including pre-absorption of the antisera with synthetic peptide hormones, indicated the specificity of the immunoreactions obtained. In all species investigated, IGF-2-immunoreactivity occurred exclusively in INS-immunoreactive cells as was found by the use of consecutive sections and double immunofluorescence on identical sections. In contrast, IGF-1-immunoreactivity co-existed with GLUC-immunoreactivity. In man, singular SOM-immunoreactive cells also contained IGF-1-immunoreactivity. Thus, IGF-1 and IGF-2 can be localized by means of immunohistochemistry in the mammalian pancreas, and can be shown to occur in different islet cell populations. It is presumed that IGF-1 derived from A-cells and/or D-cells acts on the B-cells in a paracrine manner. The co-existence of IGF-2-immunoreactivity and INS-immunoreactivity in the human, rat, and dog endocrine pancreas indicates that mammalian IGF-2 and INS genes are regulated simultaneously.     

Effects of cadmium and zinc on plasma levels of growth hormone, insulin-like growth factor I, and insulin-like growth factor-binding protein 3

Humans are constantly exposed to cadmium (Cd) as a result of the increase in air pollution and cigaret use. Zinc (Zn), which is an essential element for the metabolism of and the constituent of many enzymes, causes growth retardation in the deficiency status so at present it is often added to the diet without measuring blood levels of this element. We also aimed to observe the effects of both Cd and Zn on the plasma levels of growth hormone (GH), insulin-like growth factor I(IGF-I), and insulin-like growth factor-binding protein 3 (IGFBP-3) in this study. For this purpose, 27 young Wistar albino male rats were divided into three groups. The first group was given 50 mg/L of CdCl₂, the second group received 500 mg/L of ZnSO₄, and the third group, as a control, received only drinking water for 1 mo. At the end of this period, plasma GH, IGF-I, and IGFBP-3 of the animals were analyzed in the blood obtained. The significance between groups was evaluated with the Mann-Whitney U-test. According to our results, levels of IGF-I and IGFBP-3 in the Cd-administered group were significantly lower than those of controls (p<0.05 and p<0.01 respectively). No statistically significant difference was observed between Zn administered and control groups in terms of all three parameters. These results show that although the addition of Zn to the diet of healthy rats had no effect on the levels of GH, IGF-I, and IGFBP-3, Cd addition lowered the levels of IGF-I and IGFBP-3 but did not change the levels of GH compared to controls.     

Sulfated gastrin stimulates ghrelin and growth hormone release but inhibits insulin secretion in cattle

This study was designed to determine the effects of gastrin on the circulating levels of ghrelin, growth hormone (GH), insulin, glucagon and glucose in ruminants. Two experiments were done in eight Holstein steers. Animals were randomly assigned to receive intravenous bolus injections: (1) 0.1% bovine serum albumin in saline as vehicle, 0.8, 4.0 and 20.0 μg/kg body weight (BW) of bovine sulfated gastrin-34; (2) vehicle, 0.53 μg/kg BW of bovine sulfated gastrin-17 alone or combined with 20.0 μg/kg BW of [d-Lys³]-GHRP-6, the selective antagonist of GHS-R1a. Blood samples were collected from −10 to 150 min relative to injection time. Concentrations of acyl and total ghrelin in response to gastrin-34 injection were significantly increased in a dose-dependent manner. Concentrations of GH were also markedly elevated by gastrin-34 injection; however, the effect of 20.0 μg/kg was weaker than that of 4.0 μg/kg. The three doses of gastrin-34 equally decreased insulin levels within 15 min and maintained the level until the time of last sampling. Gastrin-34 had no effect (P > 0.05) on the levels of glucagon and glucose. Levels of acyl ghrelin increased after administration of gastrin-17 alone or combined with [d-Lys³]-GHRP-6; however, [d-Lys³]-GHRP-6 did not block the elevation of GH by gastrin-17. The present results indicate that sulfated gastrin stimulates both ghrelin and GH release, but the GHS-R1a may not contribute to the release of GH by gastrin. Moreover, sulfated gastrin seems to indirectly maintain the homeostasis of blood glucose through the down-regulation of insulin in ruminants.     

Blockade of IRS1 in isolated rat pancreatic islets improves glucose-induced insulin secretion

Several neural, hormonal and biochemical inputs actively participate in the balance of insulin secretion induced by blood glucose fluctuations. The exact role of insulin as an autocrine and paracrine participant in the control of its own secretion remains to be determined, mostly due to insufficient knowledge about the molecular phenomena that govern insulin signaling in pancreatic islets. In the present experiments we demonstrate that higher insulin receptor and insulin receptor substrates-1 and -2 (IRS1 and IRS2) concentrations are predominantly encountered in cells of the periphery of rat pancreatic islets, as compared to centrally located cells, and that partial blockade of IRS1 protein expression by antisense oligonucleotide treatment leads to improved insulin secretion induced by glucose overload, which is accompanied by lower steady-state glucagon secretion and blunted glucose-induced glucagon fall. These data reinforce the inhibitory role of insulin upon its own secretion in isolated, undisrupted pancreatic islets.     

Sensitivity of rat forebrain neurons to growth hormone-releasing hormone

The effects of iontophoretically applied human pancreatic growth hormone-releasing factor (hpGRF), peptide histidine isoleucine (PHI-27), and somatostatin (SS) on the extracellular activity of single cells in the hypothalamus, thalamus, and cortex of the rat brain were studied in urethane-anesthetized, male rats. Neurons with membrane sensitivity to hpGRF, PHI-27, and SS were present in each brain region. Although neurons excited by these peptides were encountered in thalamus and hypothalamus, depression of neuronal firing was the predominant response observed. Overall, the neurons responding to hpGRF also possessed membrane sensitivity to PHI-27, whereas, the hpGRF sensitive neurons appeared to be more divided as to their ability to respond to SS. The results clearly demonstrate that hpGRF and PHI-27 are capable of affecting the membrane excitability of neurons in several brain regions. The distribution of neurons sensitive to hpGRF suggests that hypothalamic GRF, in addition to its well documented role in the regulation of pituitary growth hormone secretion, may subserve other physiological events in the rat central nervous system as a neurotransmitter and/or neuromodulator.     

Muscle-specific expression of insulin-like growth factor I counters muscle decline in mdx mice

The Rho GTPase and Fyn tyrosine kinase have been implicated previously in positive control of keratinocyte cell-cell adhesion. Here, we show that Rho and Fyn operate along the same signaling pathway. Endogenous Rho activity increases in differentiating keratinocytes and is required for both Fyn kinase activation and increased tyrosine phosphorylation of beta- and gamma-catenin, which is associated with the establishment of keratinocyte cell-cell adhesion. Conversely, expression of constitutive active Rho is sufficient to promote cell-cell adhesion through a tyrosine kinase- and Fyn-dependent mechanism, trigger Fyn kinase activation, and induce tyrosine phosphorylation of beta- and gamma-catenin and p120ctn. The positive effects of activated Rho on cell-cell adhesion are not induced by an activated Rho mutant with defective binding to the serine/threonine PRK2/PKN kinases. Endogenous PRK2 kinase activity increases with keratinocyte differentiation, and, like activated Rho, increased PRK2 activity promotes keratinocyte cell-cell adhesion and induces tyrosine phosphorylation of beta- and gamma-catenin and Fyn kinase activation. Thus, these findings reveal a novel role of Fyn as a downstream mediator of Rho in control of keratinocyte cell-cell adhesion and implicate the PRK2 kinase, a direct Rho effector, as a link between Rho and Fyn activation.     

Involvement of growth hormone (GH) and insulin-like growth factor (IGF) system in ovarian folliculogenesis

During the last decade, involvement of growth hormone (GH), insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) in ovarian folliculogenesis has been extensively studied. This review provides an update on the GH, IGF system and their role in ovarian follicular development. In vitro studies and knockout experiments demonstrated an important role of GH in preantral follicle growth and differentiation through their binding with GH receptors, which are located both in the oocyte and follicular somatic tissues. Furthermore, GH stimulates the development of small antral follicles to gonadotrophin-dependent stages, as well as maturation of oocytes. With regard to the IGF system, IGF-I has no effects on primordial follicle development, but both IGF-I and IGF-II stimulate growth of secondary follicles. Depending on the species studies and method used, these proteins have been detected in oocytes and/or somatic cells. In antral follicles, these IGFs stimulate granulosa cell proliferation and steroidogenesis in most mammals. The bioavailability of IGFs is regulated by a family of intrafollicular expressed IGF binding proteins (IGFBPs). Facilitation of IGF can be increased through the activity of specific IGFBP proteases, which degrade the IGF/IGFBP complex, resulting in the production of IGFBP fragments and release of attached IGF.     

Phe-met-arg-phe-amide (FMRF-NH2) inhibits insulin and somatostatin secretion and anti-FMRF-NH2 sera detects pancreatic polypeptide cells in the rat islet

FMRF-NH2-like immunoreactivity was localized in the pancreatic polypeptide containing cells of the rat islet. FMRF-NH2 was investigated with regard to its effect on insulin, somatostatin and glucagon secretion from the isolated perfused rat pancreas. FMRF-NH2 (1 microM) significantly inhibited glucose stimulated (300 mg/dl) insulin release (p less than 0.005) and somatostatin release (p less than 0.01) from the isolated perfused pancreas. FMRF-NH2 (1 and 10 microM) was without effect on glucagon secretion, either in low glucose (50 mg/dl), high glucose (300 mg/dl), or during arginine stimulation (5 mM). These findings indicate that these FMRF-NH2 antisera recognize a substance in the pancreatic polypeptide cells of the islet which may be capable of modulating islet beta and D cell activity.     

Growth hormone,insulin-like growth factor I,and motoneuron size

In this study we asked whether growth hormone (GH) and one of its key mediators, insulin-like growth factor I (IGF-I), influence spinal motoneuron size in conjunction with whole body size. We present evidence that GH has such a role, possibly without the mediation of IGF-I. Both lumbar motoneuron and body size were found to be increased relative to littermate controls in transgenic mice overexpressing GH, while body size, but not motoneuron size, was increased in mice overexpressing IGF-I. GH overexpression coordinately increased nucleolar, nuclear, and cell body size in lumbar spinal motoneurons, so that their normal size relationships were preserved in the transgenic mice. In addition, spinal cord and brain weights were significantly increased in both types of transgenic animal. We conclude that GH can regulate motoneuron, central nervous system, and body size in the same animal, and that IGF-I can mimic the effects of GH on at least two of these three parameters. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 202–212, 1997.     

Separation of fast from slow anabolism by site-specific PEGylation of insulin-like growth factor I (IGF-I)

Insulin-like growth factor I (IGF-I) has important anabolic and homeostatic functions in tissues like skeletal muscle, and a decline in circulating levels is linked with catabolic conditions. Whereas IGF-I therapies for musculoskeletal disorders have been postulated, dosing issues and disruptions of the homeostasis have so far precluded clinical application. We have developed a novel IGF-I variant by site-specific addition of polyethylene glycol (PEG) to lysine 68 (PEG-IGF-I). In vitro, this modification decreased the affinity for the IGF-I and insulin receptors, presumably through decreased association rates, and slowed down the association to IGF-I-binding proteins, selectively limiting fast but maintaining sustained anabolic activity. Desirable in vivo effects of PEG-IGF-I included increased half-life and recruitment of IGF-binding proteins, thereby reducing risk of hypoglycemia. PEG-IGF-I was equipotent to IGF-I in ameliorating contraction-induced muscle injury in vivo without affecting muscle metabolism as IGF-I did. The data provide an important step in understanding the differences of IGF-I and insulin receptor contribution to the in vivo activity of IGF-I. In addition, PEG-IGF-I presents an innovative concept for IGF-I therapy in diseases with indicated muscle dysfunction.