Hepatic Insulin-like Growth factor-I mRNA Expression Research Articles

Growth and Hepatic Insulin-Like Growth Factor-I Gene Expression in Dominant and Subordinate Oreochromis Niloticus L Under Limited Period of Physical Interaction

Social stress is known to regulate several aspects of the teleost physiology. This study explored the influence of limited period of physical interaction on growth and hepatic insulin-like growth factor-I (IGF-I) messenger RNA (mRNA) expression of the fish. Twenty all-male Oreochromis niloticus were isolated for 10 days and were used in a social pair study. After the social interaction was settled, dominant and subordinate individuals in a pair were reared separately in one aquarium separated by glass divider. The fish were fed at the same rate daily to remove the possible effect of nutrition. The glass divider was removed 10 min daily for social interaction. Weight was monitored on Days 2, 7 and 14 during the experimental period, then hepatic IGF-I mRNA expression was quantified. During the 14 days social experiment, mean specific growth rate of dominant fish (1.6%·day−1) was significantly higher (P<0.01) than that of the subordinate fish (0.9%·day−1). Dominant fish also had 2.5 fold significantly higher (P<0.05) mean IGF-I mRNA expression than that of subordinate fish. These indicate that even under limited period of physical contact but with period of visual communication, social status regulates growth and hepatic IGF-I gene expression in this species of fish. There was also a significant positive correlation (r = 0.52; P<0.01) between growth and IGF-I mRNA level which supports the previous studies that hepatic IGF-I gene expression has a potential utility as an instantaneous growth rate indicator for O. niloticus.

Differential responses of the somatotropic and thyroid axes to environmental temperature changes in the green iguana

Growth hormone (GH), together with thyroid hormones (TH), regulates growth and development, and has critical effects on vertebrate metabolism. In ectotherms, these physiological processes are strongly influenced by environmental temperature. In reptiles, however, little is known about the direct influences of this factor on the somatotropic and thyroid axes. Therefore, the aim of this study was to describe the effects of both acute (48h) and chronic (2weeks) exposure to sub-optimal temperatures (25 and 18°C) upon somatotropic and thyroid axis function of the green iguana, in comparison to the control temperature (30–35°C). We found a significant increase in GH release (2.0-fold at 25°C and 1.9-fold at 18°C) and GH mRNA expression (up to 3.7-fold), mainly under chronic exposure conditions. The serum concentration of insulin-like growth factor-I (IGF-I) was significantly greater after chronic exposure (18.5±2.3 at 25°C; 15.92±3.4 at 18°C; vs. 9.3±1.21ng/ml at 35°C), while hepatic IGF-I mRNA expression increased up to 6.8-fold. Somatotropic axis may be regulated, under acute conditions, by thyrotropin-releasing hormone (TRH) that significantly increased its hypothalamic concentration (1.45 times) and mRNA expression (0.9-fold above control), respectively; and somatostatin (mRNA expression increased 1.0–1.2 times above control); and under chronic treatment, by pituitary adenylate cyclase-activating peptide (PACAP mRNA expression was increased from 0.4 to 0.6 times). Also, it was shown that, under control conditions, injection of TRH stimulated a significant increase in circulating GH. On the other hand, while there was a significant rise in the hypothalamic content of TRH and its mRNA expression, this hormone did not appear to influence the thyroid axis activity, which showed a severe diminution in all conditions of cold exposure, as indicated by the decreases in thyrotropin (TSH) mRNA expression (up to one-eight of the control), serum T4 (from 11.6±1.09 to 5.3±0.58ng/ml, after 2weeks at 18°C) and T3 (from 0.87±0.09 to 0.05±0.01ng/ml, under chronic conditions at 25°C), and Type-2 deiodinase (D2) activity (from 992.5±224 to 213.6±26.4fmolI125T4/mgh). The reduction in thyroid activity correlates with the down-regulation of metabolism as suggested by the decrease in the serum glucose and free fatty acid levels. These changes apparently were independent of a possible stress response, at least under acute exposure to both temperatures and in chronic treatment to 25°C, since serum corticosterone had no significant changes in these conditions, while at chronic 18°C exposure, a slight increase (0.38 times above control) was found. Thus, these data suggest that the reptilian somatotropic and thyroid axes have differential responses to cold exposure, and that GH and TRH may play important roles associated to adaptation mechanisms that support temperature acclimation in the green iguana.

Cysteine induces longitudinal bone growth in mice by upregulating IGF-I.

Cysteine (Cys) is known to exert various effects, such as antioxidant, antipancreatitic and antidiabetic effects. However, the effects of Cys on longitudinal bone growth have not been elucidate to date. Thus, the aim of the present study was to evaluate the effects of Cys on bone growth. Growth-plate thickness and bone parameters, such as bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), connectivity density (Conn.D) and total porosity were analyzed by means of micro-computed tomography (μCT). The levels of serum insulin-like growth factor-I (IGF-I) were measured by enzyme-linked immunosorbent assay (ELISA). Hepatic IGF-I mRNA expression was analyzed by quantitative polymerase chain reaction (qPCR). The phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 5 (STAT5) was investigated by western blot analysis. Our results revealed that Cys increased IGF-I mRNA expression in HepG2 cells. The thickness of the growth plates was increased following treatment with Cys. Moreover, BV/TV, Tb.Th, TbN, Conn.D and total porosity were improved following treatment with Cys. Hepatic IGF-I mRNA expression and serum IGF-I levels were increased by Cys. The levels of phosphorylated JAK2 and STAT5 were elevated by Cys. The findings of our study indicate that Cys increases the thickness of growth plates through the upregulation of IGF-I, which results from the phosphorylation of JAK2-STAT5. Thus, our data suggest that Cys may have potential for use as a growth-promoting agent.

Effect of KH-BaRoKer-SeongJangTang based on traditional medicine theory on longitudinal bone growth

KH-BaRoKer-SeongJangTang (KBS) is a recently developed formulation by using traditional drugs considering traditional medical theory of Oriental books such as ShinNongBonChoGyeong and JuRye, which has been used to improve the growth of child in Korea. Although KBS is usually prescribed to many children who are in retard for their age, its pharmacological effects have not been fully understood in experimental models. The aim of this study was to evaluate the effects of KBS on bone growth. Growth plate thickness and bone parameters such as bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), connection density (Conn.D), and total porosity were analyzed by means of microcomputed tomography. Serum insulin-like growth factor-I (IGF-I) levels were measured by enzyme-linked immunosorbent assay. Hepatic IGF-I mRNA expression was analyzed by real-time polymerase chain reaction. Phosphorylation of signal transducer and activator of transcription5 (STAT5) was investigated using Western blot analysis and immunohistochemistry. The thickness of growth plate was increased by KBS. BV/TV, Tb.Th, TbN, Conn.D, and total porosity were improved by KBS. Hepatic IGF-I mRNA and serum IGF-I levels were elevated by KBS. Phosphorylation of STAT5 was increased with administration of KBS. These results suggest that KBS would be helpful to children who are in retard for their age through the elevation of IGF-I.

Anti-tumor necrosis factor agent PEG-sTNFRI improves the growth hormone/insulin-like growth factor-I system in adjuvant-induced arthritic rats

Adjuvant-induced arthritis is associated with body weight loss and decreased pituitary growth hormone (GH) and hepatic insulin-like growth factor-I (IGF-I) synthesis. Cytokines as tumor necrosis factor (TNF) mediate wasting associated with chronic inflammation. The aim of this study was to analyse whether the inhibition of TNF is able to revert the decrease in the body weight and the GH/IGF-I axis in arthritic rats. Male Wistar rats were injected with Freund's adjuvant, and 15 days later arthritic and control rats were daily injected with polyethylene glycol linked to soluble TNF receptor p55 (PEG-sTNFRI) (1 mg/kg, s.c.) or saline for 8 days. There was a significant decrease in pituitary GH mRNA ( P < 0.05), hepatic IGF-I mRNA ( P < 0.01) and serum concentrations of IGF-I ( P < 0.01) in arthritic rats. The 8-day administration of PEG-sTNFRI resulted in an increase in food intake ( P < 0.05) and body weight gain ( P < 0.01) in arthritic but not in control rats. There was an increase in pituitary GH mRNA after PEG-sTNFRI treatment both in control and in arthritic rats. There was a significant increase in IGF-I serum concentrations ( P < 0.05) and hepatic IGF-I mRNA expression ( P < 0.05) in control rats treated with PEG-sTNFRI, whereas the effect of this anti-TNF agent in arthritic rats was only statistically significant in hepatic IGF-I mRNA expression ( P < 0.05). These data suggest that TNF seems to be involved in the decrease in GH and IGF-I synthesis in arthritic rats.

Effect of dietary supplementation of chitosan and galacto-mannan-oligosaccharide on serum parameters and the insulin-like growth factor-I mRNA expression in early-weaned piglets

The study was to determine effects of dietary supplementation of chitosan (COS) and galacto-mannan-oligosaccharids (GMOS) on some serum biochemical indices, serum growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels, and hepatic and long gissimus muscle IGF-I mRNA expression in early-weaned piglets. Twenty six Duroc × Landrace × Yorkshire piglets at the age of 15 days were used. The piglets had access to creep feed during the suckling. Six piglets were sacrificed for sampling at the beginning of the study. The other 20 piglets were individually housed in metabolic cages and randomly allotted to four corn and soybean meal-based diets including the control group, the antibiotic group with 110 mg lincomycin/kg diet, the COS group containing 0.025% COS, and the GMOS group with 0.20% GMOS, respectively, in a 2-week feeding experiment. Blood urea nitrogen (BUN) level was reduced whereas serum total protein concentration was increased ( P < 0.05) in responses to the COS and GMOS supplementation. Dietary supplementation of COS and GMOS also increased ( P < 0.05) the serum GH and IGF-I levels along with enhanced hepatic and the muscle IGF-I mRNA abundance. Dietary supplementation of oligosaccharides such as COS and GMOS may improve growth and feed conversion efficiency by increasing plasma GH and IGF-I levels, in the early-weaned piglets.

Alcohol-Reduced Plasma IGF-I Levels and Hepatic IGF-I Expression Can Be Partially Restored by Retinoic Acid Supplementation in Rats

Chronic and excessive ethanol intake in rats results in low levels of hepatic retinoic acid (RA) either by inhibiting the biosynthesis of RA or by enhancing its catabolism of RA. Chronic ethanol intake also decreases both hepatic expression of insulin-like growth factor-I (IGF-I) and plasma IGF-I concentration in rats. It is not known whether RA supplementation in alcohol-fed rats can restore plasma IGF-I concentrations and hepatic IGF-I expression. In the present study, we examined both plasma IGF-I level and hepatic IGF-I mRNA expression in alcohol-fed rats with or without RA (100 microg/kg body weight) supplementation for 6 mo. Hepatic IGF-I mRNA levels and plasma IGF-I concentration were decreased (84 and 29%, respectively) significantly in alcohol-fed rats compared with the control. In contrast, RA supplementation in ethanol-fed rats partially restored both hepatic IGF-I mRNA levels and plasma IGF-I concentration compared with rats fed ethanol alone. These data suggest that alcohol-impaired hepatic RA status contributes to the decreased plasma IGF-I level and hepatic IGF-I expression in alcoholics.

Establishment of a time-resolved fluoroimmunoassay for measuring plasma insulin-like growth factor I (IGF-I) in fish: effect of fasting on plasma concentrations and tissue mRNA expression of IGF-I and growth hormone (GH) in channel catfish ( Ictalurus punctatus)

A time-resolved fluoroimmunoassay (TR-FIA) was established and validated that allows for the determination of plasma concentrations of insulin-like growth factor I (IGF-I) in three domestically cultured fishes: channel catfish ( Ictalurus punctatus), hybrid striped bass ( Morone chrysops × M. saxatilis), and rainbow trout ( Oncorhynchus mykiss). Sensitivity of the assay was 0.20 ng/ml. Intra- and inter-assay coefficients of variation (CV) were <7 and <12%, respectively. Serial dilutions of plasma from each species were parallel to the standard curve. Recovery of IGF-I from spiked plasma samples was >90% for all three species of fishes. The IGF-I TR-FIA was biologically validated via its use to determine the effect of fasting on circulating IGF-I levels in channel catfish. Fasting-induced changes in plasma growth hormone (GH), hepatic IGF-I mRNA expression, and pituitary GH mRNA expression were also determined. Fasted channel catfish lost 5.6 and 15.6% body mass after 2 and 4 weeks of fasting, respectively. Plasma IGF-I concentrations were depressed ( P < 0.05) relative to fed controls following 2 and 4 weeks of fasting. Plasma GH concentrations were not different ( P > 0.05) in fasted fish after 2 weeks, but significantly increased ( P < 0.05) by 4 weeks of fasting. Hepatic IGF-I mRNA expression after 2 and 4 weeks of fasting was reduced ( P < 0.05) relative to fed controls. Pituitary GH mRNA expression was similar ( P > 0.05) between 2-week-fasted catfish and fed controls, but was increased ( P < 0.05) in 4-week-fasted catfish. The IGF-I TR-FIA was sensitive, accurate, and precise for all three species of fishes, and provided a low-cost, and non-radioisotopic method for quantifying plasma IGF-I levels in fed and fasted channel catfish.

Molecular cloning and expression of insulin-like growth factor-I (IGF-I) in Eurasian perch (Perca fluviatilis): lack of responsiveness to growth hormone treatment

The cloning of Eurasian perch (Perca fluviatilis) insulin-like growth factor-I (IGF-I) liver cDNA resulted in the identification of two transcripts of 794 and 713 nucleotides. Whereas the long IGF-Ib isoform consisted of 186 residues, the short IGF-Ia isoform was lacking 27 residues of the E domain due to alternative exon splicing. The long isoform was more abundant than the short isoform in liver, while the expression of both isoforms was rather low in non-hepatic tissues. In order to elucidate the specific endocrine regulation of growth in perch, effects of growth hormone (GH) treatment on weight gain and hepatic IGF-I expression were investigated in juvenile Eurasian perch. Fish injected with Southern black bream (Acanthopagrus butcheri, Perciformes) GH (0.5 μg/g body weight) grew significantly faster than the saline injected control group, whereas treatment with bovine GH (1.0 μg/g body weight) gave no growth enhancement. No effects of the GH treatments on hepatic IGF-I mRNA expression were shown by Northern blot analysis. Thus, the impact of GH-IGF-I axis on growth regulation in Eurasian perch remains unclear, but might be affected by IGF-binding proteins (IGFBPs).

Hepatic mRNA expression and plasma levels of insulin-like growth factor-I (IGF-I) in broiler chickens selected for different growth rates

The hepatic expression and plasma concentrations of IGF-I were investigated in three broiler chicken strains selected for different growth rates (HP-Hubbard-Pettersen, a fast growing strain; NN-Naked-neck, a strain with an intermediate growth rate and a heterozygous genotype, and C-Caipira, a slow growing crossbred strain). The chickens were studied at 1, 21 and 42 days of age and had free access to food throughout the study. Hepatic IGF-I mRNA expression was assessed by dot blot analysis using a randomly labeled chicken IGF-I cDNA as the probe and plasma IGF-I concentrations were assayed by radioimmunoassay. The hepatic levels of IGF-I mRNA increased from 1 to 21 days of age in all strains, with NN chickens showing a higher (p < 0.05) IGF-I expression than the other strains. Plasma IGF-I concentrations increased (p < 0.05) with broiler chicken age, but there were no significant differences among the strains. These results indicate that despite differences in the growth rates among the strains, the changes in the expression of IGF-I mRNA in liver and in the plasma levels of IGF-I were independent of broiler chicken strain, but varied with chicken age.

The inhibition of inducible nitric oxide synthase reverts arthritic-induced decrease in pituitary growth hormone mRNA but not in liver insulin-like growth factor I mRNA expression.

Experimental arthritis induced by Freund-adjuvant administration is a model of chronic inflammation and rheumatoid arthritis associated with a decrease in pituitary growth hormone (GH) and hepatic insulin-like growth factor I (IGF-I) gene expression. Excessive nitric oxide (NO) synthesis by inducible NO synthase (iNOS) has been implicated in the pathogenesis of inflammatory illness. Moreover, NO participates in the regulation of GH secretion at both the hypothalamus and the pituitary. We have examined the role of iNOS activation in producing the changes in the GH-IGF-I axis in arthritic rats. Adult male Wistar rats received aminoguanidine or vehicle from day 20, after adjuvant or vehicle injection, until day 28. Two hours and 30 min after the last aminoguanidine injection, all rats were killed by decapitation. Arthritis increased hypothalamic expression of somatostatin mRNA while it decreased pituitary GH mRNA expression, and both effects were prevented by aminoguanidine administration. In arthritic rats, the parallel decrease in serum IGF-I, and in hepatic IGF-I content and mRNA expression, correlates with the decrease in circulating GH concentrations. Aminoguanidine administration to arthritic rats did not modify either serum GH or serum IGF-I concentrations, or hepatic IGF-I mRNA expression. However, aminoguanidine administration to control rats resulted in a decrease in serum GH concentrations and in a decrease in both hepatic IGF-I mRNA expression and serum IGF-I concentrations. These data suggest that NO mediates the arthritis-induced decrease in GH mRNA expression by acting at a hypothalamic level, but it is not involved in the decrease in hepatic IGF-I mRNA expression.

Thyroid hormone stimulates hepatic IGF-I mRNA expression in a bony fish, the tilapia Oreochromis mossambicus, in vitro and in vivo

To gain more knowledge about the physiological regulation of hepatic insulin-like growth factor-I (IGF-I) production in bony fish, we examined the potential influence of thyroid hormone (T3, 3,5,3 ′-triiodothyronine) on the expression of IGF-I in the liver of the tilapia Oreochromis mossambicus, using in vitro and in vivo methods. The in vitro experiments were performed using a recently established primary hepatocyte cell culture and IGF-I expression was determined by means of semiquantitative RT-PCR. T3 (100 nM) significantly enhanced the synthesis rate of IGF-I mRNA in short (>8 h) and long (>42 h) time courses. The stimulating effect of T3 was detected already after 1 h. After 4 h, the IGF-I mRNA expression was more than 150% of the starting amount. In long time courses, after 6 h the IGF-I mRNA value was about 170% of that in untreated cells and at the end of the experiment, it was still three times higher than in the control. In addition, the increase in IGF-I mRNA expression evoked by T3 (1 nM to 1 μM) was dose-dependent. In the in vivo approach, 10 individuals of tilapia received 4 daily intraperitoneal injections of T3 (6 μg/g body weight). IGF-I mRNA was assessed using dot blot technique with a tilapia specific IGF-I cRNA probe. The T3 treatment led to an increase of the IGF-I mRNA level up to 45% in the liver compared to the untreated animals. In conclusion, our results show that T3 directly stimulates the hepatic production of IGF-I in the tilapia in vitro and in vivo and indicate that in tilapia liver regulatory mechanisms seem to exist, as they are discussed for mammals.

Differential Regulation of Porcine Hepatic IGF-I mRNA Expression and Plasma IGF-I Concentration by a Low Lysine Diet

The influence of dietary lysine on hepatic insulin-like growth factor-I (IGF-I) gene expression and plasma IGF-I level was investigated. Two male 6-wk-old pigs from each of six litters were used. Each littermate was assigned to one of two diets, control or low lysine (LL), that were isoenergetic and similar in protein content and provided 14.3 MJ digestible energy/kg for both diets, 185 g protein/kg for the control diet and 180 g protein/kg for the LL diet. The control diet contained all essential amino acids in the recommended amounts, including 11.5 g lysine/kg. The LL diet was similar but contained only 7 g lysine/kg. Pigs were pair-fed these diets for 3 wk. Growth rates and feed efficiencies of pigs fed the LL diet were significantly lower than those of pigs fed the control diet (P < 0.01). Plasma IGF-I levels in pigs fed the LL diet were 52% lower than in those fed the control diet (P < 0.01), and the LL group also had lower plasma IGF-binding protein-3 (IGFBP3) levels (P < 0.05). Despite the strikingly lower plasma IGF-I in pigs fed the LL diet, hepatic IGF-I mRNA abundance did not differ between the two treatment groups. We conclude that the reduction in plasma IGF-I caused by reduced dietary lysine may have been due in part to suppression of post-transcriptional events in IGF-I expression. The lower plasma IGFBP3 in pigs fed the LL diet suggests that increased clearance rates of circulating IGF-I may have been involved in this response.

Increased Expression of Insulin-like Growth Factor-I in Serum and Liver after Recombinant Human Growth Hormone Administration in Thermally Injured Rats

Background. Recombinant human growth hormone (rhGH) has been shown to modulate the hypermetabolic response and the hepatic acute-phase response after thermal injury. In vitro studies, however, demonstrated that rhGH activates insulin-like growth factor-I (IGF-I) gene transcription and production, suggesting that rhGH may exert some of its effects indirectly through IGF-I stimulation. The purpose of this study was to determine the effects of rhGH on serum and hepatic IGF-I in thermally injured rats.Methods. Sprague–Dawley rats (56 males) receiving a 60% TBSA third-degree scald burn were randomly divided to receive either rhGH (2.5 mg/kg/day im) or saline (control). Rats were sacrificed on postburn days 1, 2, 5, and 7 and serum IGF-I, hepatic IGF-I mRNA, and IGF-I protein concentration were measured. The physiologic response to changes in IGF-I levels was evaluated by measuring hepatocyte proliferation, total liver protein concentration, and muscle dry/wet weights.Results. Serum IGF-I was increased from postburn day 1 through day 7 in rats receiving rhGH compared to controls (P < 0.05). Hepatic IGF-I mRNA and IGF-I protein expression were increased from day 1 to 7 after burn in animals receiving rhGH when compared to controls (P < 0.05). Recombinant hGH increased hepatocyte proliferation at 5 days and total liver protein concentration at 5 and 7 days postburn compared to controls (P < 0.05). Muscle dry/wet weights increased in rats receiving rhGH at 7 days after burn compared to controls (P < 0.05).Summary. Liver and serum IGF-I levels decreased after a thermal injury. Recombinant hGH attenuated this decrease by stimulating hepatic IGF-I expression. Increases in IGF-I were associated with increases in hepatocyte proliferation and protein concentration in liver and muscle.Conclusion. We suggest that rhGH modulates the hypermetabolic response through IGF-I stimulation in the hepatic parenchyma.

Insulin and insulin-like growth factor I in coho salmon Oncorhynchus kisutch injected with streptozotocin

Streptozotocin (STR), an agent known to induce damage of pancreatic B cells in mammals, was used to study changes of plasma insulin concentration and hepatic insulin-like growth factor I (IGF-I) mRNA levels in juvenile coho salmon, Oncorhynchus kisutch. Fish were injected intraperitoneally with either 200 mg/kg body wt STR or the vehicle. All fish fed and grew throughout the experiment; however, the STR-injected fish had lower instantaneous growth rates than control fish (1.4% and 2.1%, correspondingly). Plasma insulin concentration and hepatic IGF-I mRNA levels in STR-treated fish were significantly lower than in the control fish, whereas there was no difference between the two groups of fish in plasma concentrations of either glucagon or growth hormone. Impaired insulin production caused by STR injection was either coincident with or slightly preceded reduction in hepatic IGF-I mRNA expression, implying that insulin may affect IGF-I production and, consequently, fish growth.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) treatment of the GH-deficient dwarf rat: differential effects on IGF-I transcription start site expression in hepatic and extrahepatic tissues and lack of effect on type I IGF receptor mRNA expression

The rat IGF-I gene consists of six exons, with exons 3 and 4 forming a ‘core’ mature IGF-I coding region to which alternate 5′ and 3′ regions are spliced. Transcription occurs from four dispersed start sites (ss) ≈ 382 (ss 1), ≈ 343 (ss 2), ≈ 245 (ss ≈ 30–40 (ss 4) basepairs (bp) from the 3′ end of exon 1, and from a region 50–70 bp from the 3′ end of exon 2. The expression of ss mRNAs displays tissue-specific and ontogenic regulation. Alternate splicing of exon 5 produces E-peptide coding domain variants (Ea and Eb mRNAs), with the Eb form found predominantly in the liver. The regulation of IGF-I mRNA expression by GH and IGF-I in the GH-deficient dwarf ( dw / dw) rat was investigated using antisense RNA probes in a solution hybridization RNase protection assay to detect leader exon and E domain variant mRNAs. GH treatment of dw / dw and normal Lewis rats increased the expression of all liver leader exon ss and E domain variants coordinately (1.6–1.9-fold increase, p < 0.01), although the increase observed in Eb transcripts was significantly higher in the dw / dw compared to the normal rat ( p < 0.05). In kidney, GH treatment significantly increased exon 1 ss 3 and ss 4 transcripts by approximately 40% ( p < 0.05). The expression of the other start sites was not affected by GH, suggesting that transcription factors may regulate start site usage independently. GH treatment was associated with a significant increase in IGF-I mRNA expression in skeletal muscle ( p < 0.05) but not cardiac muscle or spleen. IGF-I treatment was associated with minor (≈ 20%) but significant ( p < 0.05) reductions in IGF-I mRNA expression in the liver and kidney of dw / dw rats, suggesting that IGF-I can suppress IGF-I mRNA expression. IGF-I treatment did not affect IGF-I mRNA expression in cardiac and skeletal muscle of dw / dw rats. IGF-I receptor mRNA was detected in extrahepatic tissues only, and was not affected by either GH or IGF-I treatment. In summary, start site-specific regulation by GH was observed in kidney. GH increased IGF-I mRNA expression in muscle, kidney and liver, but had no effect in heart or spleen in the dw / dw rat. Our data suggest that systemic IGF-I can feedback on hepatic and renal IGF-I mRNA expression in the GH-deficient state.

Regulation of serum insulin-like growth factor-I (IGF-I), hepatic growth hormone binding and IGF-I gene expression in the rat during pregnancy and lactation

An apparent GH resistance occurs in pregnancy, since GH concentrations in serum are reported to be normal or elevated, whereas serum IGF-I falls to very low levels. To determine whether this GH resistance is manifest at the level of the hepatic GH receptor or in the ability of GH to initiate IGF-I gene expression, we have determined hepatic IGF-I mRNA expression, circulating IGF-I and hepatic GH binding during various stages of pregnancy and lactation in the rat. The concentration of IGF-I in serum fell from 37 +/- 5 nmol/l (means +/- S.E.M.) in virgin rats to 17 +/- 1 nmol/l in rats in late pregnancy, recovered in early lactation (31 +/- 3 nmol/l) but was again significantly lower than in virgin animals by mid-lactation (22 +/- 3 nmol/l). Hepatic GH binding did not vary significantly during pregnancy but showed a small significant decrease in early lactation when expressed per mg membrane protein. When expressed as GH binding per liver, however, there were no significant changes in GH binding at any stage. Liver weight increased significantly between virgin and early pregnant animals (7.1 +/- 0.2 g compared with 9.2 +/- 0.5 g respectively, P < 0.01) and continued to increase up to late lactation (14.3 +/- 0.4 g).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor I (IGF-I) mRNA expression in coho salmon, Oncorhynchus kisutch: Tissue distribution and effects of growth hormone/prolactin family proteins

To examine the hormonal and nutritional regulation of insulin-like growth factor I (IGF-I) mRNA expression, a sequence-specific solution hybridization/RNase protection assay for coho salmon IGF-I mRNA was developed. This assay is both rapid and sensitive and has low inter- (less than 15%) and intra-assay variations (less than 5%). Using this assay, the tissue distribution of IGF-I mRNA and effects of growth hormone (GH), prolactin (PRL) and somatolactin (SL) on hepatic IGF-I mRNA expression in coho salmon were examined in vivo. Liver had the highest IGF-I mRNA level of 16 pg/μg DNA. Significant amounts of IGF-I mRNA were also found in all other tissues examined (intestine 4.1, kidney 3.8, gill arch 2.4, brain 2.4, ovary 2.3, muscle 2.1, spleen 1.7 and fat 1.1 pg/μg DNA). Injection of coho salmon GH at doses of 0.1 and 1 μg/g body weight significantly increased the hepatic IGF-I mRNA levels in a dose-dependent manner. Injection of coho salmon SL, a recently discovered member of the GH/PRL family, stimulated the IGF-I mRNA expression at the higher dose (1 μg/g), whereas coho salmon PRL had no effect at either dose. Concentration-dependent stimulation by coho salmon GH was also obtained in vitro in primary culture of salmon hepatocytes in concentrations ranging from 0.01 to 1 μg/ml. These results indicate that IGF-I mRNA expression occurs in a variety of tissues in coho salmon, and that at least the hepatic expression is under the regulation of GH and possibly other hormones. The sequence-specific assay established in the present study can be used for accurate quantitation of IGF-I mRNA in salmonid species, and can contribute to a better understanding of the physiology of IGF-I in salmonids.