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We investigated the effects of 6 mo of near-physiological testosterone administration to older men on skeletal muscle function and muscle protein metabolism. Twelve older men ([greater than or equal to] 60 yr) with serum total testosterone concentrations aging; muscle strength; lean body mass; insulin-like growth factor I

The objective of the present study was to evaluate changes in equine follicular fluid insulin-like growth factor binding protein (IGFBP) proteolytic activity as well as steroid, IGF, and IGFBP concentrations during follicular development in the mare. Mares (n = 14) were classified as either in the follicular phase (n = 8) or luteal phase (n = 6). Follicles (n = 92) were categorized as small (6 to 15 mm; n = 54), medium (16 to 25 mm; n = 23), or large (> 25 mm; n = 15), and follicular fluid was collected. Estradiol and androstenedione levels in follicular fluid were greater (P < 0.05), and IGFBP-3 concentrations tended to be greater (P < 0.10) in large than in small or medium follicles, whereas IGFBP-2, -4, and -5 levels were less (P < 0.05) in large than in small or medium follicles. Estradiol and androstenedione concentrations were negatively correlated (P < 0.01) with IGFBP-2, -4, and -5 but not IGFBP-3 concentrations. To evaluate proteolysis of IGFBP, follicular fluid was incubated with human [sup.125]I-labeled IGFBP-2, -3, and -5 and protein separated by 12% SDS-PAGE. Follicular fluid caused little or no proteolysis of [sup.125]I-lableled IGFBP-2 or -3, and the small amount of proteolysis of IGFBP-2 and -3 did not differ (P > 0.10) among follicle classes. However, more [sup.125]I-labeled IGFBP-5 was cleaved (P < 0.05) by follicular fluid from large follicles collected during the follicular phase than large follicles during the luteal phase, and small or medium follicles from follicular and luteal phase mares indicating that a protease to IGFBP-5 exists in estrogen-dominant equine follicles. This IGFBP-5 protease was inhibited by kallikrein/serine protease and metalloprotease inhibitors. We conclude that the tendency of estrogen-dominant follicles of mares to have greater levels of IGFBP-3 and lesser levels of IGFBP-2 does not appear to be due to differences in proteolysis, whereas changes in IGFBP-5 levels are likely due to changes in activity of a serine protease or metalloprotease. Changes in IGFBP may alter levels of bioavailable IGF that stimulate steroidogenesis and mitogenesis in developing mare follicles. Key Words: Follicles, Insulin-like Growth Factor, Mares

Research was conducted to examine the effects of exogenous porcine growth hormone (pGH) administration on circulating insulin-like growth factor (IGF) I concentration, IGF-binding proteins, tissue growth and protein synthesis in pigs. Absolute synthesis rate was computed as the fractional rate times the tissue protein content. Results showed that pGH administration to pigs produced the desired stimulation of the somatotropic axis. They also indicated at least two possible mechanisms for increasing IGF-I circulation in pGH-treated pigs.

The effect of insulin growth factor-1 receptor kinase, on hepatocyte-expressed plasma membrane glycoprotein, pp120, was investigated through in vitro phosphorylation of recombinant pp120 in intact NIH 3T3 mouse fibroblasts cells. Data revealed that IGF-1 receptors has no capacity to phosphorylate pp120 in the presence of IGF-1. The C-terminal domain of the beta subunit plays a regulatory role in pp120 phosphorylation.

Insulin-like growth factors (IGF-1) activate skeletal muscle cell proliferation first, and then triggers events which lead to the expression of muscle-specific genes in myogenic cell cultures. This was gleaned from a detailed analysis of gene expression in L6E9 myoblast cultures treated with IGF-1 to investigate the early events preceding the stimulation of myogenic differentiation by the growth factor.

The transgene p53 controls activity of the gene which encodes the insulin-like growth factor binding protein 3 (IGF-BP3). The induction of IGF-BP3 gene expression by wild-type p53 is associated with enhanced secretion of an active form of IGF-BP3. Such a secretion prevents mitogenic signalling by the insulin-like growth factor IGF-1. Stimulation of p53 gene in EB1 colon carcinoma cells increases the concentration of mRNA encoding the IGF-BP3. Results show that IGF-BP3 is involved in the cell growth controlled by p53.

Intestinal epithelial cell line Caco-2 generates three types of insulin-like growth factor-binding proteins (IGF-BPs), IGF-BP-2, IGF-BP-3 and IGF-BP-4, with variations in their profiles with differentiation. Epidermal growth factor or transforming growth factor-alpha (TGF-alpha) and IGFs activate distinct kinds of IGF-BPs and the autocrine function of TGF-alpha influences the synthesis of IGF-BP during differentiation.

125I-labeled insulin-like growth factor I (IGF-I) aids the detection and analysis of IGF-I receptors in human esophageal epithelial (HEE) cells and helps determine their function in cell development. HEE cells comprise two classes of IGF-I receptors, high capacity low affinity receptors and low capacity high affinity receptors. IGF-I occupies low-affinity IGF-I receptors to mediate cell development.

The beta-subunit mutant 952STOP, which assembles nonfunctional hybrid rat/mutant human receptor tetramers, is a dominant negative suppressor of endogenous insulin-like growth factors I (IGF-I) receptor function. IGF-I, which is a mitogenic growth factor, participates in tumorigenesis.

An analysis of DNA preparation of cultured chromaffin cells from fetal, neonatal and adult rats, to study the influence of insulin-like growth-factors (IGF3), nerve growth factors (NGF) and basic fibroblast growth factor (bFGF), confirms the synergistic nature of the joint influence of IGF3 and bFGF or NGF. Nuclear 5-bromo-21-deoxydine incorporation to around the same level as 10nm IGF-I or IGF-II resulted from addition of 1nM bFGF or 2nM NGF in neonatal and adult cells.

An analysis of proximal nephron growth-regulating adaptations to hypophysectomy confirms IGF binding protein 5 (IGFBP-5) and IGF-I receptor regulation in hypophysectomized rat kidneys. IGF-I, which restricts degradation and ensures growth factor interaction with the receptor, involves IGFBP-5 as an extravascular reservoir. Lowered circulating levels of IGF-I may involve ligand secretion.

An analysis of the 14-residue peptide, associated with Arg2410-Lys2423 of the insulin-like growth factor II receptor (IGF-IIR), demonstrates the transformation of G-protein specificity from the adenylate cyclase-binding protein Gi to the stimulating protein Gs. A short receptor site and intact cells were used to activate G-protein-complexed receptor signals.

An analysis of growth hormone (GH) responses in porcine kidney F+ cells revealed the different effects of growth hormone and IGF-I on glutamine/glutamate utilization. IGF-I and GH increased and decreased glutamine/glutamate consumption, respectively. GH also enhanced levels of synthesized acids to 30-50% above the basal standard in the monolayers that were grown in laboratory conditions. Recombinant human GH treatment of monolayers grown on porous supports led to a decline in net glucose uptake.

An analysis of the reduction of apoptosis in cerebellar granule neurons by low potassium reveals that differentiated granule neurons degenerate and die, when they are shifted from a culture medium with high K+ to one with a low, but more physiological K+ concentration. Apoptosis or programmed cell death is responsible for death by low potassium.

The mouse cDNA for the alpha subunit was cloned and studied to reveal that the nucleotide sequence of the mouse receptor is homologous to the alpha subunits of rat and human insulin-like growth factor I receptors (IGF-IR). The predicted polypeptide chain composition of the mouse receptor resembles the rat and human IGF-IRs. The active tetrameric IGF-IR glycoprotein complex is similer to its conformational configuration and biological functions.

A biologically active amino acid sequence called insulin-like growth factor 1B-(103-124) E1 amide (IBE1) has been located inside the E peptide of the insulin-like growth factor IB (IGF-IB) precursor. A flanking Gly-Lys-Lys-Lys, a signal sequence for sequential protolytic cleavage and peptidyl C-terminal amidation, predicted the existence of this sequence. An alternate mRNA resembling the midsection of the human IGF-IB E domain should be generated in species where an IGF-I mRNA with homology to the human IGF-IB E domain has not yet been elucidated.

Although chronic diarrhea affects heart function and morphology, the pathogenic mechanisms are unknown. It was our hypothesis that diarrhea imposes metabolic stress to inhibit the synthesis of new contractile proteins. To test this hypothesis, we investigated the effects of lactose-induced diarrhea in rats. The groups were: 1) freely fed controls, 2) rats with lactose-induced diarrhea or 3) pair-fed rats. After 1 wk, hearts from the rats were subjected to subcellular fractionation techniques to isolate the major protein fractions, including myofibrillar proteins. The rates of protein synthesis were measured with concomitant assay of cardiac composition and plasma analytes. In comparison with the control group, diarrhea induced the following changes (P [is less than] 0.05): a decrease in heart Weight, reduced RNA and mixed protein contents and a reduction in the fractional rate of mixed protein synthesis. There was a reduction in the content of all protein fractions. The fractional synthesis rate was reduced only for the myofibrillar fraction. Plasma insulin-like growth factor-I, but not corticosterone, was reduced. Plasma cholesterol and triglyceride concentrations were also reduced. In comparison with the pair-fed group, diarrhea induced the following changes (P [is less than] 0.05): a reduction in heart weight and fractional rate of mixed protein synthesis, reduced myofibrillar absolute synthesis rate and increased sarcoplasmic/myofibrillar fractional synthesis rate ratio. Plasma bicarbonate, triglyceride and urea concentrations were reduced, with an increase in albumin. Diarrhea impaired cardiac biochemistry, including a reduction in protein content and synthesis. A substantial proportion of these changes is due to anorexia, but the selective reduction in the synthesis of contractile proteins is a feature exclusive to the diarrhea group and may be due to reductions in plasma insulin-like growth factor-I. J. Nutr. 131: 1513-1519, 2001. KEY WORDS: * diarrhea * heart * protein synthesis * rats insulin-like growth factor

The insulin-like growth factors (IGFs) in extracellular fluids are bound to several high affinity binding proteins (IGFBPs). The circulating IGF/IGFBP complexes prolong the half-lives of IGFs and buffer the acute hypoglycemic effects of IGFs. Locally expressed IGFBPs may also provide a means of localizing IGFs in defined areas and may alter IGF bioactivity by modulating the ligand receptor interaction. In this paper, we report the cloning of an IGFBP cDNA from the gilthead seabream, Sparus aurata. The cDNA encodes a protein of 285 amino acids. The primary structure of this protein is 43~49% identical to that of zebrafish, chicken, rat, mouse, and human. The sequence identity of seabream IGFBP-2 with other human IGFBPs ranges from 28-34%. Northern blot analysis revealed that the seabream IGFBP-2 transcript is approximately 1.8 kb and is highly expressed in the liver. Analysis of IGFBP-2 mRNA in various adult tissues using RT-PCR revealed its expression in all tissues studied, with the highest levels in liver, skin, gonad and pyloric caeca. The hepatic mRNA levels of IGFBP-2 were greatly reduced in growth hormone-treated animals. This data is in agreement with the role of IGFBP-2 function as a negative growth regulator in the growth hormone-IGF-I axis. Transcripts for IGFBP2 were detected throughout early development in unfertilized eggs, embryos and larvae, with highest levels observed on days 3-6 after hatching, suggesting that this mRNA is the product of both the maternal and embryonic genomes. These data suggest that IGFBP-2 is expressed from the earliest stages of development and may play an important role in regulating growth and development in fish (Supported by BARD Grant IS-2769096R and NSF Grant IBN-9728911).

Parenteral nutrition with lipid or glucose suppresses liver growth and response to GH in adolescent male rats. Am J Physiol Endocrinol Metab 281: E1063-E1072, 2001.--Our aim was to investigate the effects of modifying the carbohydrate-to-lipid ratio of parenteral nutrition (PN) on body composition and the anabolic actions of insulin-like growth factor I (IGF-I) and growth hormone (GH). Adolescent male Sprague-Dawley rats were randomized to receive 7 days of GH, IGF-I (3.5 mg * [kg.sup.-1] * [day.sup.-1] for both) or placebo while receiving high-carbohydrate PN (CHO-PN), high-lipid PN (L-PN), or an oral diet (chow) (the PN protocols were isonitrogenous and isocaloric). PN impaired muscle growth, which was reversed by GH in the CHO-PN group only (P < 0.03). PN increased carcass lipid (P < 0.02), the effect being greater in the L-PN than in the CHO-PN group (P < 0.001). Visceral lean tissue growth was significantly impaired by PN (P < 0.001). IGF-I reversed this impairment, but GH had no effect. PN impaired the normal increase in hepatic protein and DNA (P < 0.001) and produced liver steatosis (P < 0.001). However, this steatosis was less in L-PN than in CHO-PN (P < 0.001). Serum IGF-I and the acid-labile subunit (ALS) were decreased by PN (P < 0.001) and were not affected by GH during PN treatment. However, GH significantly increased serum ALS concentrations in the chow-fed rats (P = 0.032). In conclusion, modifying the CHO-to-L ratio of PN had no significant effect on IGF-I action, but CHO-PN increased the peripheral effect of GH. L-PN increased carcass lipid significantly and decreased hepatic steatosis. Nevertheless, PN caused significant liver steatosis and profound impairment of hepatic cell growth, which was associated with relative hepatic GH resistance. growth hormone; parenteral nutrition; organ composition; body composition; insulin-like growth factor I treatment; steatosis; liver impairment