Probing the disulfide folding pathway of insulin-like growth factor-I

The crucial step of folding of recombinant proteins presents serious challenges to obtaining the native structure. This problem is exemplified by insulin-like growth factor (IGF)-I which when refolded in vitro produces the native three-disulfide structure, an alternative structure with mispaired disulfide bonds and other isomeric forms. To investigate this phenomenon we have examined the refolding properties of an analog of IGF-I which contains a 13-amino acid N-terminal extension and a charge mutation at position 3 (Long-[Arg3]IGF-I). Unlike IGF-I, which yields 45% of the native structure and 24% of the alternative structure when refolded in vitro, Long-[Arg3]IGF-I yields 85% and 10% of these respective forms. To investigate the interactions that affect the refolding of Long-[Arg3]IGF-I and IGF-I, we acid-trapped folding intermediates and products for inclusion in a kinetic analysis of refolding. In addition to non-native intermediates, three native-like intermediates were identified, that appear to have a major role in the in vitro refolding pathway of Long-[Arg3]IGF-I; a single-disulfide Cys18-Cys61 intermediate, an intermediate with Cys18-Cys61 and Cys6-Cys48 disulfide bonds and another with Cys18-Cys61 and Cys47-Cys52 disulfide bonds. Furthermore, from our kinetic analysis we propose that the Cys18-Cys61, Cys6-Cys48 intermediate forms the native structure, not by the direct formation of the last (Cys47-Cys52) disulfide bond, but by rearrangement via the Cys18-Cys61 intermediate and a productive Cys18-Cys61, Cys47-Cys52 intermediate. In this pathway, the last disulfide bond to form involves Cys6 and Cys48. Finally, we apply this pathway to IGF-I and conclude that the divergence in the in vitro folding pathway of IGF-I is caused by non-native interactions involving Glu3 that stabilize the alternative structure.     

The effects of dietary protein restriction on chronic progressive renal disease

There have been a large number of clinical trials and two meta-analyses attempting to determine if dietary protein restriction retards the rate of renal disease progression. Indeed, in a systematic search of prospective, controlled trials examining the effects of protein restriction over at least 6 months, we located 23 published between 1980 and 1996. Only 12 of these trials were randomized and controlled. The results of the 23 studies were heterogeneous. Two meta-analyses combined the results of randomized, controlled trials. Although both meta-analyses concluded that dietary protein restriction significantly reduced the number of patients who died or required treatment for end-stage renal disease, the well-known effects of protein restriction on the signs and symptoms of uremia leave open the question of whether protein restriction had a substantial effect on renal disease progression per se. Adding to the uncertainty is the inconclusive result of the largest, best-designed clinical trial, the Modification of Diet in Renal Disease Study. In any case, the effect of protein restriction on the rate of decline in renal function is arguably modest, making it difficult to demonstrate statistical significance, even in large, well-designed clinical trials. All of these trials suggest that we need therapies that are more effective than dietary protein restriction to halt the progression of renal disease.     

Localisation of insulin-like growth factor-I (IGF-I) immunoreactivity in the olivocerebellar system of developing and adult rats

The molecular mechanisms which underlie the development of the olivocerebellar topography are not fully understood. Insulin-like growth factor-I (IGF-I) is a growth factor known to play important roles in neural development and it has been identified within the cerebellum and the inferior olive. To assess the contribution of IGF-I to the development of climbing fibre topography, the distribution of IGF-I-like immunoreactivity (IGF-I IR) was identified in the cerebellar cortex and inferior olive of rats, 0, 3, 5, 7, 10, 15, 21, 28 and 90 days old. In the cerebellar cortex, IGF-I IR was localised solely to Purkinje cells and its distribution was spatially and temporally regulated in a manner which coincides with climbing fibre development. At birth, weak IGF-I IR was detected in a few Purkinje cells in the ventral vermis. More Purkinje cells became positive until at postnatal day 7(P7) all Purkinje cells displayed IGF-I IR. Subsequently, a subpopulation of Purkinje cells lost their reactivity for IGF-I to leave IGF-I-positive cells organised into sagittal bands by P15. IGF-I IR was also seen in all subdivisions of the inferior olive between birth and P10 in a distribution which paralleled the maturation of the inferior olive. The Purkinje cell and inferior olivary IGF-I IR parallels climbing fibre development and thus the results of this study support the hypothesis that IGF-I is involved in the development of climbing fibre topography.     

Pharmacokinetics of recombinant human insulin-like growth factor-I in diabetic rats

Pharmacokinetics of recombinant human insulin-like growth factor-I (rhIGF-I) was investigated after iv administration (0.32, 1.0, and 3. 2 mg/kg) to normal and streptozotocin-induced diabetic rats. rhIGF-I was eliminated from plasma biexponentially in both normal and diabetic rats. Plasma concentrations of rhIGF-I were lower at almost all the time points examined in diabetic rats than in normal rats. The pharmacokinetic parameters of total body clearance (CLtotal), mean residence time (MRT), and elimination rate constant (kel) indicated that rhIGF-I disappeared more rapidly in diabetic rats than in normal rats at any dosage. The amounts of IGF binding proteins (IGFBPs) in plasma were assessed by determining the endogenous IGF-I and. Levels of the 150 kDa complex, a ternary complex of IGF-I with IGFPB-3 and an acid-labile subunit, the 50 kDa complex, a complex of IGF-I with IGFBP-2, were found to be lower in diabetic rats than in normal rats. Fractions of rhIGF-I free and bound to the binding proteins were estimated by gel chromatographic separation of rhIGF-I in plasma after iv administration, and the pharmacokinetics of free and bound rhIGF-I was analyzed independently. Plasma concentrations of free and bound rhIGF-I were lower in diabetic rats than in normal rats, especially the concentrations of the 150 kDa complex were much lower. The reduced IGFBP-3 would be responsible for the faster elimination of rhIGF-I in diabetic rats.     

Postnatal catch-up growth induced by growth hormone and insulin-like growth factor-I in rats with intrauterine growth retardation caused by maternal protein malnutrition

In an earlier study, we found that yellow-rumped warblers had in vitro active uptake rates of D-glucose that were only a few percent of the glucose absorption rate achieved at the whole-animal level. Here we used a pharmacokinetic technique to test whether a substantial amount of sugar can be absorbed passively. We used yellow-rumped warblers (Dendroica coronata), known for their seasonal frugivory, freely feeding on a synthetic mash formulated with naturally occurring concentrations of D-glucose. Birds absorbed 89.8% +/- 1.0% (SE) of the D-glucose in the mash. When fed the same mash with trace-labeled 3H L-glucose, the stereoisomer that does not interact with the intestinal Na(+)-glucose cotransporter, 3H appeared in plasma, an indication that this stereoisomer of glucose was absorbed. We used 3H levels in plasma and excreta in a pharmacokinetic model to calculate L-glucose extraction efficiency (i.e., the percent absorbed). Calculated mean extraction efficiency for the passively absorbed L-glucose averaged 91% +/- 23%. Our finding of considerable passive absorption reconciles the in vitro and in vivo results for D-glucose absorption and is in concert with results from five other avian species. The passive pathway appears to provide birds with an absorptive process that can respond quickly to changing luminal concentration and that is energetically inexpensive to maintain and modulate in real time but that may bear a cost. Less discriminate passive absorption might increase vulnerability to toxins and thus constrain foraging behavior and limit the breadth of the dietary niche.     

Androgen regulation of the insulin-like growth factor-I and the estrogen receptor in rat uterus and liver

For the first time testosterone is shown to be an important regulator of the insulin-like growth factor-I (IGF-I) in the rat uterus under in vivo conditions. In this study the regulation of IGF-I and the estrogen receptor (ER) by gonadal steroids in the uterus and liver of female rats was monitored. The ER level was assayed by hormone binding after treatment with testosterone, 5 alpha-dihydrotestosterone or estradiol and specific mRNA species were analyzed by a solution hybridization/RNase protection assay using 35S-labeled RNA probes. Ovariectomized rats restored uterine weight after treatment with testosterone. Uterine IGF-I mRNA was more than 20-fold higher in testosterone treated rats compared to untreated ovariectomized controls after 48 h treatment. The effects of testosterone on ovariectomized animals was followed in a timecourse study. Testosterone administration increased uterine IGF-I mRNA expression during the first 48 h and the maximally induced level was maintained throughout the duration of the experiment (168 h). Since induction of IGF-I mRNA by estrogen is transient, these data indicate that androgen and estrogen increase IGF-I mRNA by different mechanisms. Regulation of IGF-I mRNA by gonadal steroids was also studied in hypophysectomized animals. The rats were given either testosterone, 5 alpha-dihydrotestosterone or estradiol, and uterine IGF-I mRNA was measured after 1 week of treatment. At this timepoint estrogen treated rats showed levels of IGF-I mRNA not significantly different from those of hypophysectomized controls. In contrast testosterone and 5 alpha-dihydrotestosterone increased the IGF-I mRNA level 30 and 40 times, respectively, relative to hypophysectomized control animals. Since 5 alpha-dihydrotestosterone is not convertable to estrogen, the induction by testosterone was considered to be a true androgenic phenomenon.     

Effect of protein restriction on the messenger RNA contents of bone-matrix proteins, insulin-like growth factors and insulin-like growth factor binding proteins in femur of ovariectomized rats

It has been reported that loss of ovarian oestrogen after menopause or by ovariectomy causes osteoporosis. In order to elucidate the effect of dietary protein restriction on bone metabolism after ovariectomy, we fed ovariectomized young female rats on a casein-based diet (50 g/kg diet (protein restriction) or 200 g/kg diet (control)) for 3 weeks and measured mRNA contents of bone-matrix proteins such as osteocalcin, osteopontin and alpha 1 type I collagen, insulin-like growth factors (IGF) and IGF-binding proteins (IGFBP) in femur. Ovariectomy decreased the weight of fat-free dry bone and increased urinary excretion of pyridinium cross-links significantly, although dietary protein restriction did not affect them. Neither ovariectomy nor protein restriction affected the content of mRNA of osteopontin and osteocalcin; however, ovariectomy increased and protein restriction extensively decreased the alpha 1 type I collagen mRNA content in bone tissues. Ovariectomy increased IGF-I mRNA only in the rats fed on the control diet. Conversely, protein restriction increased and ovariectomy decreased the IGF-II mRNA content in femur. Furthermore, the contents of IGFBP-2, IGFBP-4 and IGFBP-5 mRNA increased, but the content of IGFBP-3 mRNA decreased in femur of the rats fed on the protein-restricted diet. In particular, ovariectomy decreased the IGFBP-2 mRNA content in the protein-restricted rats and the IGFBP-6 mRNA content in the rats fed on the control diet. These results clearly show that the mRNA for some of the proteins which have been shown to be involved in bone formation are regulated by both quantity of dietary proteins and ovarian hormones.     

Independent effects of food intake and insulin status on insulin-like growth factor-I in young pigs

The successful use of proteins in pharmaceutical and other commercial applications requires close examination of their relative fragility. Because of the resultant enhanced stability, proteins are often formulated in the solid state, even though dehydration tends to alter their structure. Even in the solid form, however, proteins may become inactivated due to various deleterious processes, e.g., aggregation. This review focuses on such mechanisms, with an emphasis on case studies conducted in our laboratory. Proteins which have both disulfide bonds and free thiols may aggregate via thiol-disulfide exchange, and this process may be facilitated by lyophilization-induced structural perturbations. For proteins possessing disulfides but not free thiols, aggregation also may occur when native disulfides are beta-eliminated, thus giving rise to thiol species which can catalyze disulfide scrambling. Other deleterious processes have also been uncovered, including a formaldehyde-mediated aggregation of formalinized vaccines. It is illustrated how knowledge of such deterioration pathways makes possible the rational development of stable solid protein formulations.     

A multicenter study on insulin-like growth factor-I serum levels in children with chronic inflammatory diseases

OBJECTIVE: To study insulin-like factor-I (IGF-I) levels in children and adolescents with connective tissue diseases (CTDs), compare them with values obtained in normal controls, and correlate them with age, sex, steroid treatment, and inflammatory parameters. METHODS: A multicenter, cross-sectional study was performed in 3 Italian pediatric rheumatology centers. The subjects studied comprised 117 patients with juvenile arthritis (53 systemic, 25 pauciarticular and 17 polyarticular) and other CTDs (22), and 78 children without inflammatory conditions. IGF-I levels were measured by radioimmunoassay after acid-ethanol extraction. RESULTS: Mean IGF-I serum levels were 167.6 ng/ml (+/- 132.5) in patients and 214.4 (+/- 142.8) in controls. A significant correlation was found between IGF-I levels and age in the controls (P = 0.001), but not in the patients. Covariance analysis with age as the covariate showed significantly lower IGF-I levels in the patient group (P = 0.001). No significant correlation was found between IGF-I levels and the total quantity of steroid taken. Multiple regression analysis showed that IGF-I levels were inversely correlated with the ESR (P = 0.0001) and positively correlated with age (P = 0.0002) and sex (P = 0.021) in the patient group. CONCLUSION: IGF-I serum levels are decreased in patients with CTDs; inflammation could play a major role.     

Role of growth hormone and insulin-like growth factor-I in mammary development

Mammary glands from 3- to 4-week-old mice were incubated in whole organ culture to determine the effects of GH, PRL, and insulin-like growth factor-I (IGF-I) on lobulo-alveolar development and milk protein expression. Virgin mice were implanted with pellets of estrogen and progesterone (1:1000). After 9 days, abdominal no. 4 glands were removed and place on siliconized lens paper in Waymouths' medium supplemented with insulin (Ins), aldosterone, hydrocortisone, and epidermal growth factor. Concentrations of bovine GH, ovine GH, rat GH, or ovine PRL added to the medium varied from 0-1 micrograms/ml. IGF-I was added to replace either Ins or PRL up to 1 microgram/ml. When glands were incubated with Ins, aldosterone, hydrocortisone, and 250 ng/ml PRL, they exhibited lobulo-alveolar development and expressed the milk protein beta-casein. When GH was substituted for PRL, little lobulo-alveolar development occurred, although beta-casein mRNA was expressed at low levels. Either PRL or GH at 1 microgram/ml induced lobulo-alveolar development and beta-casein mRNA. Addition of epidermal growth factor to whole organ culture with GH or PRL (1 microgram/ml) was equally effective in stimulating lobulo-alveolar development. IGF-I did not substitute for PRL, GH, or insulin in tissue maintenance. It is clear that GH at high concentrations can act directly on mouse mammary tissue to induce both lobulo-alveolar development and casein expression.     

Comparison of the effects of growth hormone, insulin-like growth factor-I and fetal calf serum on mouse molar odontogenesis in vitro

The effects of growth hormone, its mediator insulin-like growth factor-I (IGF-I), and fetal calf serum on odontogenesis were compared to those of serum-free medium. Explanted, 16-day, fetal mouse first molar tooth germs in early bell stage were grown on semisolid, serum-free medium supplemented with ascorbic and retinoic acids. Recombinant human growth hormone at 50 or 100 ng/ml, IGF-I at 100 or 200 ng/ml, or fatal calf serum at 20% concentration were added to the media. Volumetric changes in serial sections of six tooth germs per treatment over 3 days of treatment (4, 5, 6 days in vitro) were compared by digitized morphometry. Mitotic indices were also compared and the cell densities of the dental papillae recorded. Qualitative ratings of differentiation were ascribed to each tooth germ by light microscopy. Differences in volume, mitotic activity and cell densities were found. The growth hormone-treated tooth germs were not larger than the serum-free ones but had increased mitotic indices and higher cell densities in the dental papillae. IGF-I-treated tooth germs had larger volumes than with all other treatments, e.g. germs treated with 200 ng/ml of IGF-I, after 6 days in culture, were significantly larger than with all other treatments (p<0.01-<0.001). Whilst IGF-I-treated germs displayed the greatest extent of differentiation, growth hormone-treated germs also showed advanced differentiation compared to those on serum-free medium. These results suggest that growth hormone and IGF-I are involved in odontogenesis of murine teeth in vitro by affecting mitotic activity, tissue volume and cell differentiation. In conjunction with previous immunohistochemical studies that show expression of growth hormone receptor and IGF-I in developing teeth, these results provide evidence that both growth hormones and its mediator play a part in odontogenesis.     

Islet amyloid polypeptide decreases the effects of insulin-like growth factor-I on glucose transport and glycogen synthesis in skeletal muscle

Previous studies have shown that islet amyloid polypeptide (IAPP) is co-secreted with insulin from the beta-cell. IAPP reduces insulin-stimulated rates of glycogen synthesis in skeletal muscle but the mechanisms are unclear. Insulin-like growth factor I (IGF-I) is an important regulator of glucose metabolism in skeletal muscle and acts through its own receptor, which has many structural and functional similarities with the insulin receptor. Despite this, the effects of IGF-I on glucose utilization are not identical to those of insulin. The aim of the study was to determine the effects of IAPP on IGF-I-stimulated rates of glucose transport and metabolism (measured by 3-O-methyl[3H]glucose and [U-14C]glucose, respectively) in rat soleus muscle, and compare them with those simulated by insulin. IAPP (10 nM) decreased the sensitivity of 3-O-methylglucose transport, the flux of glucose to hexosemonophosphate and the sensitivity of glycogen synthesis to IGF-I. In contrast, IAPP had no effect on IGF-I-stimulated rates of lactate formation (i.e., glycolysis). IAPP decreased the sensitivity of 3-O-methylglucose transport and glycogen synthesis to insulin. It is concluded that IAPP blunts the stimulation of glucose uptake and deposition by IGF-I or insulin in skeletal muscle. These observations expand those made initially for IAPP and insulin and suggest that IAPP affects IGF-I- or insulin-stimulated glucose metabolism in muscle by a mechanism which is common for both hormones. These experiments may serve as a framework for future studies in order to clarify the mechanisms by which IAPP affects glucose metabolism in skeletal muscle.     

Divergent effects of short-term, very-low-calorie diet on insulin-like growth factor-I and insulin-like growth factor binding protein-3 serum concentrations in premenopausal women with obesity

Patients who have sustained alcohol-related injuries are frequently treated in departments of oral and maxillofacial surgery. Often, an alcohol intervention will not be possible in accident and emergency departments due to intoxication but, when attending out-patient clinics for follow-up, patients are usually sober. This presents a unique opportunity for encouraging patients to review their alcohol consumption at a time when their facial injury may make them more receptive to advice. This article reviews the convincing evidence of the effectiveness of advice and brief interventions designed to be incorporated into standard out-patient consultations and describes practical screening of patients for harmful drinking, the Stages of Change Model of behaviour change and motivational interviewing for facilitating behavioural change.     

Histomorphometric, physical, and mechanical effects of spaceflight and insulin-like growth factor-I on rat long bones

Pituitary adenylate cyclase activating peptide and vasoactive intestinal peptide belong to the same neuropeptide family. Both peptides are present in nerve fibers in the gastric wall and are thought to be involved in the regulation of inflammatory processes. Experimental ulcers were induced in the rat gastric mucosa by local application of acetic acid. During the healing process we examined the PACAP and VIP innervation by means of immunohistochemistry and in situ hybridization. The ulcer area was examined from day 1 to day 15 after ulcer induction. There was a marked depletion of PACAP in nerve fibers at the ulcer margin from day 1 and onwards. On day 10 and day 15, PACAP-immunoreactive nerve fibers could again be visualized at the ulcer margin. In contrast, VIP immunoreactive nerve fibers were present at the ulcer margin at all time points studied. From day 10 following ulcer induction PACAP- and VIP- immunoreactive nerve fibers were increased in frequency in the smooth muscle beneath the ulcer. An upregulation of VIP and PACAP mRNA was also demonstrated in the myenteric ganglia adjacent to ulcer. The present results indicate that neuronal PACAP and VIP react differently to the inflammation at the ulcer margin but similarly in the smooth muscle during the ulcer healing.     

Muscle reinnervation following neonatal nerve crush. Interactive effects of glycosaminoglycans and insulin-like growth factor-I

This study shows that glycosaminoglycans promote muscle reinnervation following neonatal sciatic nerve injury. Such an effect appears to be mediated by insulin-like growth factor-1. The glycosaminoglycan moiety of proteoglycans is a constituent of the basal lamina active on nerve regeneration by means of the interaction with laminin and with several growth factors. We have previously shown that supplementation of glycosaminoglycans affects neuronal degeneration and regeneration. In this study we report that following neonatal lesion of the rat sciatic nerve glycosaminoglycan treatment promoted extensor digitorum longus muscle reinnervation with consequent improvement of muscle morphology. In saline-treated rats, reinnervation was only partial and there was a marked muscle fibre atrophy. In addition glycosaminoglycan treatment of lesioned rats increased insulin-like growth factor-I messenger RNA and protein in the reinnervated muscle, and insulin-like growth factor-I and insulin-like growth factor binding protein-3 plasma levels. Similarly, treatment of nerve lesioned rats with insulin-like growth factor-I promoted muscle reinnervation and prevention of muscle fibre atrophy, higher levels of insulin-like growth factor-I in the reinnervated muscle and of insulin-like growth factor-I and insulin-like growth factor binding proteins in plasma. These data suggest that glycosaminoglycans are potent stimulants of muscle reinnervation and that their effects may be mediated by increased levels of insulin-like growth factor-I.     

Low doses of insulin-like growth factor-I improve nitrogen retention and food efficiency in rats with early cirrhosis

N-Methyl-D-aspartate receptors are thought to be involved in synaptic signaling within the hypothalamo-neurohypophysial system, but the extent and nature of their involvement has not been determined. In this study, in the rat, we evaluated the effect of hyperosmotic stimulation on the N-methyl-D-aspartate receptor subunit, NR1, which confers function to N-methyl-D-aspartate receptor heteromers. Co-localization of immunoreactivity for NR1 and vasopressin- or oxytocin-associated neurophysin in magnocellular neurons of the supraoptic and paraventricular hypothalamic nuclei was accomplished using double-label immunohistochemistry. Our results show that vasopressin- and oxytocin-neurophysin-positive populations contained detectable levels of NR1 labeling. Using NR1 labeling as a measure of N-methyl-D-aspartate receptor density, we examined the effect of dehydration in these nuclei. Using computer-assisted densitometry, we found significantly greater NR1 labeling densities in the magnocellular regions of both the supraoptic and paraventricular nuclei of saline-treated rats than of control rats. This increase was not due to methodological factors, since no changes in NR1 labeling density were found in a nearby nucleus, the nucleus reuniens. Western blot analysis showed similar selective increases in NR1 labeling in homogenates from the supraoptic nucleus, paraventricular nucleus and in some cases from the anterior hypothalamic area. In both immunohistochemical and western blotting experiments we did not observe a dehydration-induced increase in NR1 in other brain areas examined. Our results showing an up-regulation of NR1-containing N-methyl-D-aspartate receptors during dehydration suggest that these receptors are involved in the regulation of body water and may represent an adaptive physiological response following activation of the hypothalamo-neurohypophysial axis. In addition, these results suggest that the functional expression of N-methyl-D-aspartate receptors is dynamic and may be modified according to the physiological state of the animal.     

Serum insulin-like growth factor-I, insulin-like growth factor binding protein-3, sex steroids, osteocalcin and bone mineral density in male and female rats

Although it has been reported that the rate of weight gain and linear growth increases markedly during puberty in rats, little is known about the relationship between endocrine changes and bone mineral density (BMD) changes upon sexual maturation in these animals. The aim of this study was to examine the levels of serum insulin-like growth factor-I (IGF-I), IGF binding protein (IGFBP)-3, sex steroids and osteocalcin, and the changes in BMD in normal aging male and female rats. Male rats exhibited increases in serum IGF-I and IGFBP-3 concentrations before increases in serum testosterone levels. IGF-I and testosterone peaked at 9 weeks of age, and thereafter remained in a steady state, whereas IGFBP-3 reached a peak at 7 weeks of age, and then gradually declined. A strong correlation between serum IGF-I and IGFBP-3 levels was found in subjects 3-9 weeks old. A highly significant correlation between serum IGF-I and testosterone levels was also found. In females, serum 17 beta-estradiol, IGF-I and IGFBP-3 levels increased gradually from 3 to 5 weeks old, peaked at 9 weeks, and then decreased slowly thereafter. The correlation coefficient between serum IGF-I and IGFBP-3 was highly significant. The correlation coefficient between serum IGF-I and 17 beta-estradiol levels was weak, although it was strongest when the subjects were 3-9 weeks old. Serum osteocalcin is a marker of bone formation; its level remained relatively high from 3 to 9 and from 3 to 7 weeks of age in males and females, respectively, although osteocalcin in both sexes declined gradually with age. As for bone mass, sharp increases in BMD in the tibia, femur and lumbar vertebrae appeared earlier in female than in male rats, and the BMD in females tended to be higher than in males between 5 and 9 weeks old. After 9 weeks of age, BMD in males was higher than that in females, as BMD in males continued to increase whereas females tended to remain in a steady state after this stage. The correlation coefficients between tibial BMD and serum IGF-I or IGFBP-3 levels were highly significant when the subjects were from 3 to 9 weeks old. Taken together, these results suggest that BMD development occurs earlier in female than in male rats. This sex-related difference in changes in the BMD pattern may result from the earlier onset of puberty in females, and from sex-specific differences in concentrations of IGF-I, IGFBP-3 and sex steroids during maturation.     

Expression of insulin-like growth factor-I gene in normal and diabetic rat eye

The expression of insulin-like growth factor I (IGF-I) gene was studied in both normal and diabetic rat eyes via in situ hybridization. The results revealed the regional expression of IGF-I gene in the rat eyes. The expression of IGF-I mRNA in the internal nuclear layer and ganglion cell layer is strong, in choroid, retinal pigment epithelium and external nuclear layer is moderate, in sclera is weak in degree and no such mRNA is detected in the cornea. The abundance of IGF-I mRNA in diabetic eye tissues is significantly (P < 0.05 or P < or = 0.01) higher than that in normal eye. These findings suggest that (1) functionally, the eye ball be considered to be an "IGF-I paracrine-autocrine system", and (2) the high expression of IGF-I indicate its initiation of diabetic retinopathy and its promotion of the progression of the lesion.