Serum levels of the acid-ethanol soluble component of non-suppressible insulin-like activity in untreated and treated streptozotocin-diabetic rats

Insulin-like growth factor: receptor and binding proteins in human retinal endothelial cell cultures of diabetic and non-diabetic origin

Human retinal endothelial cell (HREC) cultures of diabetic and non-diabetic origin were examined for the production of insulin-like growth factor I (IGF-I), IGF-I receptor and IGF-binding proteins (IGFBPs) using colloidal gold quantitative immunocytochemistry and quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR). The levels of immunoreactivity for IGF-I receptor and for four IGFBPs (IGFBP-1, -2, -3 and -5) were significantly increased in diabetic HREC cultures. Moreover, diabetic HREC cultures showed significantly less immunoreactivity for IGF-I and for IGFBP-4 as compared to non-diabetic HREC cultures. Message levels for IGF-I decreased two-fold in diabetic HREC and correlated with protein levels. Message levels for IGFBP-1, -2 and -5 increased 1.5-, 1.7- and 1.6-fold, respectively, in diabetic HREC and correlated with protein levels. However, the protein levels for IGF-I receptor and IGFBP-3 and -4 did not correlate with mRNA levels. There were no differences in mRNA levels for IGF-I receptor and IGFBP-3 and -4 between diabetic and non-diabetic HREC cultures, suggesting a post-transcriptional regulation of IGF-I receptor and the two IGFBPs. The net effect, however, supports enhanced IGF-I action in HREC cultures of diabetic origin which is an important cellular event in diabetic retinopathy.

Effects of cimaterol administration on plasma concentrations of various hormones and metabolites in Friesian steers

The aim of the experiment was to determine the acute and chronic effects of the beta-agonist, cimaterol, on plasma hormone and metabolite concentrations in steers. Twelve Friesian steers (liveweight = 488 +/- 3 kg) were randomly assigned to receive either 0 (control; n = 6) or .09 mg cimaterol/kg body weight/day (treated; n = 6). Steers were fed grass silage ad libitum. Cimaterol, dissolved in 140 ml of acidified distilled water (pH 4.2), was administered orally at 1400 hr each d. After 13 d of treatment with cimaterol or vehicle (days 1 to 13), all animals were treated with vehicle for a further 7 d (days 14 to 20). On days 1, 13 and 20, blood samples were collected at 20 min-intervals for 4 hr before and 8 hr after cimaterol or vehicle dosing. All samples were assayed for growth hormone (GH) and insulin, while samples taken at -4, -2, 0, +2, +4, +6 and +8 hr relative to dosing were assayed for thyroxine (T4), triiodothyronine (T3), cortisol, urea, glucose and non-esterified fatty acids (NEFA). Samples taken at -3 and +3 hr relative to dosing were assayed for IGF-I only. On day 1, cimaterol acutely reduced (P less than .05) GH and urea concentrations (7.6 vs 2.9 +/- 1.4 ng/ml; and 6.0 vs 4.9 +/- 0.45 mmol/l, respectively; mean control vs mean treated +/- pooled standard error of difference), and increased (P less than .05) NEFA, glucose and insulin concentrations (160 vs 276 +/- 22 mumol/l, 4.1 vs 6.2 +/- 0.15 mmol/l and 29.9 vs 179.7 +/- 13.9 microU/ml, respectively). Plasma IGF-I, T3, T4 and cortisol concentrations were not altered by treatment. On day 13, cimaterol increased (P less than .05) GH and NEFA concentrations (7.7 vs 14.5 +/- 1.4 ng/ml and 202 vs 310 +/- 22 mEq/l, respectively) and reduced (P less than .05) plasma IGF-I concentrations (1296 vs 776 +/- 227 ng/ml). Seven-d withdrawal of cimaterol (day 20) returned hormone and metabolite concentrations to control values. It is concluded that: 1) cimaterol acutely increased insulin, glucose and NEFA and decreased GH and urea concentrations, 2) cimaterol chronically increased GH and NEFA and decreased IGF-I concentrations, and 3) there was no residual effect of cimaterol following a 7-d withdrawal period.

[Principles and clinical significance of insulin-like growth factors/somatomedins]

The Insulin-like Growth Factors (IGFs) or Somatomedins are polypeptide growth factors which are similar to insulin in respect to their aminoacid sequence, structure and biologic activities. The IGFs bind to high affinity receptors which are present on many cells and in many tissues. In the circulation the IGFs are bound to transport (binding) proteins (IGF-BPs). In this review the physiologic role, the basic chemistry and the gene expression of this family of growth factors is summarized systematically. The pathophysiology of growth disorders, diabetes mellitus, malnutrition, liver and kidney disease in relation to the IGFs as well as the therapeutic and diagnostic potentials of these peptides are discussed in detail.

The effect of ovarian function on insulin-like growth factor I plasma levels and hepatic IGF-I mRNA levels in diabetic rats treated with insulin

When insulin was administered to streptozotocin-induced diabetic female rats, the percentage of glycohemoglobin, growth rate, ovulatory cycle, uterus to body weight ratio, and insulin-like growth factor (IGF-I) level returned to near normal. In untreated diabetic rats there were no normal estrous cycles, and hepatic IGF-I mRNA (7.94 +/- 1.02 O.D. units per micrograms total RNA) levels were significantly lower than the control or insulin-treated groups in proestrus (16.47 +/- 0.91 and 17.15 +/- 1.84, respectively). Insulin therapy restored the hypothalamic-pituitary-ovarian axis with the reinstitution of normal estrous cycles. Plasma IGF-I levels were highest in non-diabetic proestrous animals (277 +/- 36.9 ng/ml), significantly higher than IGF-I levels in insulin-treated diabetic rats in diestrus (174 +/- 23.1 ng/ml), non-diabetic diestrus rats (165 +/- 18.4 ng/ml) and untreated diabetic rats (135 +/- 19.7 ng/ml). Plasma IGF-I levels were elevated in insulin-treated diabetic rats in proestrus (221 +/- 78.3 ng/ml), however this was not significantly different from any other group. The increases observed in plasma IGF-I and hepatic IGF-I mRNA after insulin therapy correlate with the normalization of sex hormone secretion. Though this study does not prove a causal relationship between restoration of ovarian function and normalization of circulating IGF-I levels, a relationship has been established, as evidenced by higher levels of IGF-I in both the control and insulin-treated diabetic proestrous groups when compared to the diestrus groups.

Somatomedin-C (SM-C). Study in diabetic patients with and without retinopathy

In the present study we evaluated somatomedin-C (Sm-C) plasma levels in diabetic patients, with and without retinopathy. One hundred and thirty four diabetic patients (65 type I and 69 type II) and 90 controls, strictly matched for age and sex, were enrolled in the study. Ophthalmoscopy and fluorescein angiography allowed to distinguish: 49 patients without retinopathy, 45 patients with background retinopathy, and 40 with proliferative retinopathy. Growth hormone (GH) and Sm-C plasma levels were measured using a pool of 20-24 blood samples over 24h. Sm-C levels in type I (0.62 +/- 0.11 U/ml) and type II (0.56 +/- 0.09 U/ml) patients were significantly decreased (p less than 0.01) when compared to controls (0.89 +/- 0.30 U/ml). The mean daily secretion of GH was significantly (p less than 0.01) greater in diabetic patients (7.8 +/- 2.6 ng/ml) than in controls (4.1 +/- 1.5 ng/ml), but no correlation was found between Sm-C and GH (r = 0.15; p = n.s.). Our findings did not show any correlation between Sm-C plasma levels and either the existence of retinopathy, regardless of the degree of microvascular damage, or duration of the disease, or degree of metabolic control, as evaluated by HbA1c.

Glucocorticoid effects on IGF-1/somatomedin-C and somatomedin inhibitor in streptozotocin-diabetic rats

Diabetes is associated with a fall in serum levels of insulin-like growth factor-1/somatomedin-C (IGF-1/Sm-C) and a rise in somatomedin inhibitor, a factor which antagonizes somatomedin action. We attempted to determine if the presence of glucocorticoids was required for diabetes-related alterations in these circulating growth factors. Diabetes was induced with streptozotocin in intact or adrenalectomized rats. Adrenalectomized-nondiabetic and adrenalectomized-diabetic rats were given either no glucocorticoids or daily hydrocortisone acetate at 0.5 or 50 mg/kg body weight, and killed 48 hours after streptozotocin treatment. After serum fractionation via size exclusion high performance liquid chromatography (HPLC), IGF-1/Sm-C was determined by radioimmunoassay, and somatomedin inhibitor by bioassay according to the ability of serum fractions to blunt cartilage stimulation by normal serum. Intact-diabetic rats had 22% weight loss, glucose 427 mg/dL, and beta-hydroxybutyrate 7.2 mmol/L (all P less than .001 v control). Serum IGF-1/Sm-C levels in intact-diabetic rats were decreased 71%, while somatomedin inhibitor rose to 470% of the control values (both P less than .004). Adrenalectomized-diabetic rats displayed comparable hyperglycemia (greater than 400 mg/dL) and decline in IGF-1/SmC, with or without glucocorticoid replacement. However, adrenalectomized-diabetic rats had greatly reduced weight loss (10%), beta-hydroxybutyrate (1.5 mmol/L), and somatomedin inhibitor (59% of control), all P less than .01 v intact-diabetic. Hydrocortisone 0.5 mg/kg in these animals increased weight loss but had no significant effect on beta-hydroxybutyrate or somatomedin inhibitor levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of proteoglycans by IGF I and II in microvessel and large vessel endothelial cells

Endothelial cells were cultured from bovine capillaries and pulmonary arteries, and the effect of insulinlike growth factor (IGF) I and II (multiplication-stimulating activity) and insulin on the synthesis of proteoglycans was determined. IGF I and II stimulated 35SO4 incorporation into proteoglycans in a dose-dependent manner in both microvessel and pulmonary artery endothelial cells with maximum threefold increases. In pulmonary artery cells, the IGFs caused a general stimulation of all classes of glycosaminoglycan-containing proteoglycans. In microvessel endothelial cells, the IGFs appeared to preferentially increase heparan sulfate-containing proteoglycans. Insulin, at concentrations up to 10(-6) M, had no effect on the synthesis of proteoglycans in either microvessel or pulmonary arterial endothelial cells. Thus, the IGFs stimulate the synthesis of proteoglycans in both microvessel and large vessel endothelial cells, a property that is not mimicked by insulin. Because vascular endothelial cells are bathed by IGFs in vivo, such IGF-mediated functions are likely to be significant in both the normal physiology of vascular endothelium and in disease states such as diabetes mellitus.

Nutrition and somatomedin. XIV. Altered levels of somatomedins and somatomedin inhibitors in rats with streptozotocin-induced diabetes

Diabetes is associated with poor growth despite elevated levels of growth hormone (GH). Skeletal GH effects are mediated by somatomedins; in diabetes, somatomedins measured by radioassay are normal, yet somatomedin activity measured by bioassay is low. Since bioassay measurements reflect the presence of both somatomedins and somatomedin inhibitors, we asked if diabetes might be associated with discordant regulation of these circulating factors. Graded severity of diabetes was induced in rats by injection of streptozotocin at 37, 73, 146, and 293 mg/kg. After two days, metabolic derangement varied from normal serum beta-hydroxybutyrate with slight increase in glucose and minimal weight loss at 37 mg/kg streptozotocin to beta-hydroxybutyrate 10.6 mmol/L, glucose 447 mg/dL, and 33 g weight loss at 293 mg/kg streptozotocin. After fractionation of serum on Sephacryl S-300 pH 7.0, somatomedins and somatomedin inhibitors were measured by rat cartilage bioassay. Somatomedins (Kav 0.25 to 0.50) were comparable to control levels despite beta-hydroxybutyrate 2 mmol/L, glucose 534 mg/dL, and weight loss 11 g at 73 mg/kg streptozotocin and fell only at higher streptozotocin dosage. In contrast, somatomedin inhibitors (Kav 0.62 to 0.88) began to rise at 37 mg/kg streptozotocin and increased with higher dosage. Levels of somatomedins were correlated weakly only with beta-hydroxybutyrate (r = 0.48, P less than 0.05), while somatomedin inhibitors were correlated significantly with all indices, particularly beta-hydroxybutyrate (r = 0.78, P less than 0.0001). The early rise in somatomedin inhibitors but late fall in somatomedins could explain low somatomedin activity (and poor growth) despite normal levels of somatomedins measured by radioassay; measurement of somatomedin inhibitors may provide an index of growth potential in diabetes mellitus.

Changes in rat liver prolactin binding sites in diabetes are sex dependent

The effect of streptozotocin-induced diabetes (100 mg/kg) on lactogenic binding sites, measured by iodinated ovine prolactin (PRL) binding, has been studied in liver microsomal membranes from males and female rats. In females, specific binding was reduced in diabetes from 13% to 4.5% of total tracer, while in males specific binding increased from 0.5% to 2.5%. Similar results were obtained using iodinated human growth hormone as tracer, through overall binding was higher. Scatchard plots of binding curves in females showed that changes in binding were due to changes in receptor concentration, while affinity remained unchanged at 2 X 10(9) M-1. In diabetes, serum PRL and estradiol levels fell by 60% in males but showed no significant change in females, and could therefore not account for receptor changes. In contrast, mean testosterone levels fell in diabetic males from 9.0 to 3.9 nM, and rose in diabetic females from 2.1 to 5.8 nM. Estrogen treatment of male rats caused a marked induction of binding in nondiabetic animals, and a change from the male to the female response to diabetes. Testosterone treatment of nondiabetic females suppressed binding, although not to the male levels, and diabetes caused further suppression. These results are consistent with a role for testosterone in regulating PRL receptors in experimental diabetes, but suggest that other hormonal influences are also involved.

Increased somatomedin and cartilage metabolic activity in rabbit fetuses injected with insulin in utero

The effect of insulin injection in fetal rabbits on plasma somatomedin activity and cartilage metabolism was investigated. One fetus in each of 12 litters was injected with 1 unit of insulin zinc suspension subcutaneously on day 27 of gestation and a control fetus was injected with the same volume of 0.154 mol/l saline. The litter was delivered by caesarean section on day 29 and each fetus identified. Plasma somatomedin activity was determined by fetal rabbit cartilage bioassay. Costal cartilage from individual fetuses was incubated in medium containing [3H]thymidine or [35S]sulphate as indicators of cell replication and matrix synthesis respectively. Individual values for somatomedin activity or cartilage isotope uptake were ranked within a litter. In each case the rank in the litter of the insulin-injected fetus, but not the saline-injected fetus, was significantly higher than the mean rank of the litter. Insulin did not stimulate cartilage metabolism in vitro.

Endocrine influences on serum acid-ethanol soluble non-suppressible in insulin-like activity (NSILA-S)

Serum levels of the acid-ethanol soluble component of non-suppressible insulin-like activity (NSILA-S) have been measured by bioassay in patient with hyperprolactinaemia, hypothyroidism, thyrotoxicosis and diabetes mellitus, and in normal subjects administered prednisone, oestrogens of androgens. Hyperprolactinaemia per se did not influence serum NSILA-S, however when GH was deficient prolactin hypersecretion may have maintained serum NSILA-S. Thyroid hormones, insulin and steroids did not appear to influence serum NSILA-S. These results suggest that regulation of the serum concentration of NSILA-S is not a common effector mechanism by which these hormones influence statural growth in man.