Enhanced proteolytic activity directed against the N-terminal of IGF-I in diabetic rats

We have recently identified in serum an acid protease which is capable of generating des(1-3)IGF-I from intact IGF-I. Here we have utilized a synthetic substrate with the sequence, biotin-G-P-E-T-L-C-BSA which contains the N-terminal sequence of IGF-I, to investigate the levels of this protease activity in streptozotocin-diabetic rats. Protease activity, quantified in terms of the amount of the biotin label lost, was determined in serum and hepatic extracts from normal control rats, diabetic rats and insulin-treated diabetic rats. Both the serum protease activity and protease activity in hepatic extracts were significantly increased in diabetic rats compared with control rats (P<0.02 and P<0.005). Following acute administration of insulin, a rapid and marked reduction in serum protease activity was observed; with an approximately 50% reduction apparent at 30 min (P<0.001). Chronic insulin treatment of diabetic rats also significantly reduced the serum and hepatic protease activity to the levels seen in control rats. A positive correlation between protease activity and serum glucose level was observed (r=0.58, P<0.005). The abundance of Spi 2.1 mRNA, a serine protease inhibitor, capable of inhibiting the IGF-I protease activity in vitro, was significantly decreased in the liver of diabetic rats and insulin treatment of diabetic rats did not normalize Spi 2.1 mRNA levels. These data suggest that the conversion of IGF-I to the more active des(1-3)IGF-I variant may be enhanced in diabetic animals. Since serum IGF-I levels are reduced in diabetic rats, increased des(1-3)IGF-I-generating protease activity would enhance the functional activity of the circulating IGF-I.

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Altered release of growth hormone from dispersed adenohypophysial cells of streptozotocin diabetic rats. I. Effects of growth hormone releasing factor and somatostatin

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y89-209 ◽

1989 ◽

Vol 67 (10) ◽

pp. 1315-1320 ◽

Cited By ~ 3

Author(s):

M. S. Sheppard ◽

B. A. Eatock ◽

R. M. Bala

Keyword(s):

Growth Hormone ◽

Early Morning ◽

Serum Glucose ◽

Diabetic Rats ◽

Hormone Release ◽

Growth Hormone Release ◽

Growth Hormone Releasing Factor ◽

Rat Growth ◽

Streptozotocin Diabetic Rats

As growth hormone has been implicated in the "dawn phenomenon," an early morning rise in serum glucose, we have studied the control of growth hormone release in diabetes using an acutely dispersed system of adenohypophysial cells from normal or diabetic rats (65 mg/kg streptozotocin, 8 days before sacrifice; serum glucose, 490 ± 17 mg/dL). Growth hormone release is normally controlled by the two hypothalamic hormones, growth hormone releasing factor and somatostatin. We have found cells of the diabetic rats exhibit changes in sensitivity that result in increased growth hormone release in static incubation. In normal cells, rat growth hormone releasing factor increases growth hormone release three- to four-fold with an EC50 of 151 ± 27 pM (n = 7). In contrast, in cells from diabetic rats, there was a significant (twofold) increase in sensitivity to growth hormone releasing factor (EC50 = 75 ± 15 pM, n = 7) which resulted in increased growth hormone release with lower but not maximal (10 nM) growth hormone releasing factor. Basal nonstimulated release was unchanged. Somatostatin inhibition of stimulated growth hormone release was reduced (n = 7); half-maximal inhibition occurred with 0.21 ± 0.03 nM (normal) and 0.76 ± 0.17 nM somatotatin (diabetic). In perifusion the peak secretion rate was significantly lower for diabetic cells stimulated by a maximal dose of growth hormone releasing factor. These studies suggest somatotrophs of diabetic rats have altered sensitivity in vitro to the controlling hormones growth hormone releasing factor and somatostatin.Key words: growth hormone, diabetes, streptozotocin, growth hormone releasing factor, somatostatin.

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Effects of a high-glucose environment on the pituitary growth hormone-releasing hormone receptor: type 1 diabetes compared with in vitro glucotoxicity

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00141.2007 ◽

2008 ◽

Vol 294 (4) ◽

pp. E740-E751 ◽

Cited By ~ 6

Author(s):

Karine Bédard ◽

Julie Strecko ◽

Karyne Thériault ◽

Julie Bédard ◽

Christelle Veyrat-Durebex ◽

...

Keyword(s):

High Glucose ◽

Time Course ◽

Diabetic Rats ◽

Pituitary Cells ◽

Mrna Levels ◽

Mrna Transcript ◽

Protein Levels ◽

Igf I

The present study investigated the effects of diabetes and high glucose on GHRH receptor (GHRH-R) mRNA and protein levels in the pituitary of diabetic rats 2, 21, and 60 days post-streptozotocin (post-STZ) administration. Two days post-STZ, the 2.5-kb GHRH-R mRNA transcript was increased. Twenty-one days post-STZ, both the 2.5- and 4-kb transcripts and a 72-kDa 125I-GHRH-GHRH-R complex were elevated. Sixty days post-STZ, the 4-kb transcript remained increased and the 45-kDa 125I-GHRH-GHRH-R complex (functional receptor) was decreased. Hypothalamic GHRH mRNA and serum total IGF-I levels were reduced at all three time points. To better understand the role of high glucose on GHRH-R regulation, time-course effects of 33 compared with 6 mM d-glucose (DG) were examined in cultured anterior pituitary cells from 2-mo-old healthy rats. Membrane lipoperoxidation was present in 33 mM DG, and GHRH-R mRNA levels were diminished after 24 h, Fluo-GHRH internalization was marginal after 16–24 h, and GHRH-induced cAMP levels were decreased after 24 and 48 h. Altogether, these results indicate that the increase of the 2.5-kb GHRH-R mRNA transcript in vivo could be a consequence of a decrease of hypothalamic GHRH mRNA levels in STZ rats. Since it does not affect primarily functional GHRH-R levels, the initial diminution of circulating IGF-I levels could result from a decreased GHRH-R stimulation by GHRH. Thus, the effect of glucotoxicity would be related to a decrease of functional GHRH-R protein, as observed in rats 60 days post-STZ and in cultured pituitary cells from healthy rats exposed to a high-glucose environment.

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Differential expression of the insulin-like growth factor binding proteins in spontaneously diabetic rats

Journal of Molecular Endocrinology ◽

10.1677/jme.0.0080155 ◽

1992 ◽

Vol 8 (2) ◽

pp. 155-163 ◽

Cited By ~ 20

Author(s):

J. Luo ◽

L. J. Murphy

Keyword(s):

Growth Factor ◽

Binding Proteins ◽

Insulin Treatment ◽

Diabetic Rats ◽

Mrna Levels ◽

Insulin Like Growth Factor ◽

Intensive Insulin Treatment ◽

Igf I ◽

Spontaneously Diabetic Rats ◽

Igfbp 3

ABSTRACT Diabetes-induced growth retardation in the rodent is associated with both reduced circulating insulin-like growth factor-I (IGF-I) and enhanced levels of inhibitors of somatomedin activity. IGF-binding proteins (IGFBPs) are present in the circulation and tissue fluids and are believed to modulate the actions of IGF-I. Since elevated concentrations of the IGFBPs may contribute to the enhanced somatomedin-inhibitor activity observed in serum from diabetic animals, we have examined the amounts of hepatic IGFBP-1, -2, -3 and -4 mRNA in the spontaneously diabetic BioBreeding/Worcester rat. The study used two types of diabetic animal: mildly diabetic animals, which received suboptimal insulin treatment (0.5–1 U/day) and diabetic animals, which received intensive insulin treatment (3–6 U/day). A significant increase in the amount of IGFBP-1 and IGFBP-2 mRNA was seen 1 month and 3 months after the onset of diabetes. Intensive insulin treatment for 3 weeks normalized the amount of IGFBP-1 mRNA in diabetic rats and resulted in a decrease in IGFBP-2 mRNA. In contrast to the increase in IGFBP-1 and IGFBP-2 mRNA, a significant decrease in IGFBP-3 mRNA was seen in diabetic rats (54.6% of control, P < 0.0005 and 64.6% of control, P < 0.005 for 1 and 3 months respectively) and intensive insulin treatment for 3 weeks did not restore the IGFBP-3 mRNA level in diabetic rats. No significant difference in IGFBP-4 mRNA levels was seen in diabetic compared with non-diabetic rats. When serum was analysed by ligand blotting the major finding was a reduction in the 39–42kDa binding protein. No increase in 29–30kDa IGFBP in the serum was detected in the diabetic rats. From these studies we conclude that the major change in IGFBPs in mildly hyperglycaemic spontaneously diabetic rats is a decrease in IGFBP-3. The changes in hepatic IGFBP-1 and -2 mRNA do not appear to be of sufficient magnitude to result in an increase in serum concentrations of these binding proteins.

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Abnormalities of pancreatic somatostatin secretion corrected by in vivo insulin treatment of streptozotocin-diabetic rats

Diabetes ◽

10.2337/diabetes.30.10.865 ◽

1981 ◽

Vol 30 (10) ◽

pp. 865-867 ◽

Cited By ~ 4

Author(s):

E. R. Trimble ◽

P. P. Gerber ◽

A. E. Renold

Keyword(s):

Insulin Treatment ◽

Diabetic Rats ◽

Somatostatin Secretion ◽

Streptozotocin Diabetic Rats

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The adrenergic beta-receptor adenylate cyclase system in heart and lymphocytes from streptozotocin-diabetic rats. In vivo and in vitro evidence for a desensitized myocardial beta-receptor

Diabetes ◽

10.2337/diabetes.32.12.1110 ◽

1983 ◽

Vol 32 (12) ◽

pp. 1110-1116 ◽

Cited By ~ 18

Author(s):

O. Gotzsche

Keyword(s):

Adenylate Cyclase ◽

Diabetic Rats ◽

Adenylate Cyclase System ◽

Beta Receptor ◽

Streptozotocin Diabetic Rats

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Oxidative Stress in Rats After 60 Days of Hypergalactosemia or Hyperglycemia

International Journal of Toxicology ◽

10.1177/109158180302200603 ◽

2003 ◽

Vol 22 (6) ◽

pp. 423-427 ◽

Cited By ~ 17

Author(s):

Mary Otsyula ◽

Matthew S. King ◽

Tonya G. Ketcham ◽

Ruth A. Sanders ◽

John B. Watkins

Keyword(s):

Oxidative Stress ◽

Lipid Peroxidation ◽

Superoxide Dismutase ◽

Glutathione Peroxidase ◽

Insulin Treatment ◽

Diabetic Rats ◽

Diabetic Rat ◽

Glutathione Disulfide ◽

Hepatic Lipid Peroxidation ◽

Streptozotocin Diabetic Rats

Two of the models used in current diabetes research include the hypergalactosemic rat and the hyperglucosemic, streptozotocin-induced diabetic rat. Few studies, however, have examined the concurrence of these two models regarding the effects of elevated hexoses on biomarkers of oxidative stress. This study compared the activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase and the concentrations of glutathione, glutathione disulfide, and thiobarbituric acid reactants (as a measure of lipid peroxidation) in liver, kidney, and heart of Sprague-Dawley rats after 60 days of either a 50% galactose diet or insulin deficiency caused by streptozotocin injection. Most rats from both models developed bilateral cataracts. Blood glucose and glycosy-lated hemoglobin A1c concentrations were elevated in streptozotocin diabetic rats. Streptozotocin diabetic rats exhibited elevated activities of renal superoxide dismutase, cardiac catalase, and renal and cardiac glutathione peroxidase, as well as elevated hepatic lipid peroxidation. Insulin treatment of streptozotocin-induced diabetic rats normalized altered markers. In galactosemic rats, hepatic lipid peroxidation was increased whereas glutathione reductase activity was diminished. Glutathione levels in liver were decreased in diabetic rats but elevated in the galactosemic rats, whereas hepatic glutathione disulfide concentrations were decreased much more in diabetes than in galactosemia. Insulin treatment reversed/prevented all changes caused by streptozotocin-induced diabetes. Lack of concomitance in these data indicate that the 60-day galactose-fed rat is not experiencing the same oxidative stress as the streptozotocin diabetic rat, and that investigators must be cautious drawing conclusions regarding the concurrence of the effects of the two animal models on oxidative stress biomarkers.

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Effects of refeeding of undernourished and insulin treatment of diabetic neonatal rats on IGF and IGFBP

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1996.271.2.e223 ◽

1996 ◽

Vol 271 (2) ◽

pp. E223-E231 ◽

Cited By ~ 6

Author(s):

L. Goya ◽

F. Rivero ◽

M. A. Martin ◽

R. Arahuetes ◽

E. R. Hernandez ◽

...

Keyword(s):

Growth Hormone ◽

Body Weight ◽

Growth Factor ◽

Mrna Expression ◽

Insulin Treatment ◽

Diabetic Rats ◽

Insulin Like Growth Factor ◽

Neonatal Rats ◽

Igf I ◽

Serum Gh

The effect of refeeding and insulin treatment of undernourished and diabetic neonatal rats, respectively, on the regulation of insulin-like growth factor (IGF) and insulin-like growth factor binding protein (IGFBP) was investigated. The changes in body weight, insulinemia, glycemia, serum IGF-I, and growth hormone (GH) as well as the increase of the 30-kDa IGFBP in undernourished and diabetic neonatal rats previously shown elsewhere were reversed by refeeding and insulin treatment, respectively. Also, changes in liver mRNA expression of IGF-I and-II and IGFBP-1 and -2 were restored in refed undernourished and IGF-I and IGFBP-1 levels recovered in insulin-treated diabetic rats. However, serum GH was still below normal after rehabilitation in both situations. Thus the present results support the idea of a GH-independent IGF/ IGFBP regulation mediated by a balance of insulin and nutrients as has already been suggested in previous neonatal studies.

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Loss of sensitivity to cholecystokinin stimulation of isolated pancreatic acini from genetically diabetic rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1995.268.3.e531 ◽

1995 ◽

Vol 268 (3) ◽

pp. E531-E536 ◽

Cited By ~ 1

Author(s):

M. Otsuki ◽

T. Akiyama ◽

H. Shirohara ◽

S. Nakano ◽

K. Furumi ◽

...

Keyword(s):

Serum Glucose ◽

Diabetic Rats ◽

Exocrine Function ◽

Guanine Nucleotide Binding Protein ◽

Rat Serum ◽

Pancreatic Acini ◽

Isolated Pancreatic Acini ◽

Long Evans ◽

Oletf Rat

Pancreatic exocrine function of a new inbred strain Otsuka Long-Evans Tokushima Fatty (OLETF) rat that develops spontaneous persistent hyperglycemia was evaluated in in vitro isolated pancreatic acini and compared with that in the control Long-Evans Tokushima Otsuka (LETO) rat. Serum glucose and insulin concentrations in the OLETF rats were significantly high (glucose: 270 +/- 12 vs. 208 +/- 10 mg/100 ml, P < 0.01; insulin: 12.4 +/- 1.7 vs. 4.9 +/- 0.6 ng/ml, P) < 0.01), whereas pancreatic wet weight was significantly low (803 +/- 20 vs. 1,138 +/- 17 mg, P < 0.01) compared with those in the LETO rat. Pancreatic acini isolated from the OLETF rat were totally insensitive to cholecystokinin (CCK)-8 stimulation at concentrations of up to 100 nM. However, neither the responsiveness nor the sensitivity to carbamylcholine, bombesin, and secretin of the acini from the OLETF rat was altered or even increased, probably due to the larger amylase content in the OLETF rat acini compared with those of the LETO rat acini (31.5 +/- 2.0 vs. 13.0 +/- 1.1 Somogyi units/micrograms DNA, P < 0.01). The responsiveness to fluoride, a direct activator of guanine nucleotide-binding protein, in the OLETF rat acini was similar to that in the LETO rat, suggesting that the transmembrane signaling and effectors and subsequent intracellular signal transduction molecules in the OLETF rat acini are normal. Moreover, 125I-CCK binding to the acini prepared from the OLETF rat was totally absent. These present results indicate that the OLETF rat has a selective defect in the binding of CCK to its receptors on the acinar cell surface.

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