Scanning electron microscopic examinations on retarded bone defect healing in spontaneously diabetic BB/O(ttawa)K(arlsburg) rats

To date, no detailed knowledge from animal experiments is available on the kind and extent of osseous and mineral metabolic disorders in genetically determined, insulin-dependent Type I diabetes. The purpose of this study was to examine the influence of the diabetic metabolic state in spontaneously diabetic BB/O(ttawa)K(arlsburg) rats on bone defect healing. Eighty spontaneously-diabetic BB/OK rats with a blood-glucose value of 391 +/- 106 mg% (mean +/- SD) at the time of manifestation were used in the study. Based on blood-glucose values at the time of surgery (mg%), postoperative blood-glucose course (mg%) and postoperative insulin requirements (IU/kg), the animals were divided into groups with well-compensated (n = 40, 170 +/- 101 mg%; 221 +/- 120 mg%; 2.1 +/- 1 IU/kg) or poorly compensated (n = 40; 371 +/- 158 mg%; 357 +/- 83 mg%; 5.2 +/- 1.4 IU/kg) metabolic state. Forty LEW.1A rats served as the normoglycemic controls (95 +/- 18 mg%). Using a 1-mm-diameter Kirschner wire, a hole of femoral bone ca. 1 cm proximal to the knee joint space was centrally drilled. Ten animals from each group were killed on postoperative days 7, 14, 24, and 42, and specimens were taken for analysis. Using SEM to measure regions of new bone semiautomatically and quantitatively, also determining the number, area, and circumference of regions not yet filled with new bone. Up to postoperative day 14, very significant differences (p < 0.0001) for all investigated characteristics were found between the spontaneously-diabetic BB/OK rats and the control animals--in favor of the controls--and up to postoperative day 24 within the group of spontaneously-diabetic BB/OK rats, where the well-compensated animals had significantly better results in terms of number and area of regions of bone not yet filled with new bone formations. Forty-two days postoperatively, SEM observations showed no differences between examination groups. The process of bone defect healing in spontaneously-diabetic rats was disturbed only in the early phase and exhibited retardation in its progression. After 42 days, bone defect healing was complete, regardless of the diabetic metabolic state; no differences were detected with the SEM between examination groups at this time point.     

Gonadal dysfunction in the spontaneously diabetic BB rat: alterations of testes morphology, serum testosterone and LH

Serum testosterone, luteinizing hormone (LH), testicular histology and ultrastructure were examined in 91 spontaneously diabetic BB, semi-starved, and control Wistar rats. Between 80-120 days of age serum testosterone was decreased (1.67 +/- .25 vs. 2.95 +/- .48 ng/ml; P less than .05) in the BB rats compared to controls but not different from semi-starved rats. LH values were similar in control and BB rats (49.4 +/- 10.9 vs. 46.8 +/- 6.2 ng/ml). Abnormal lipid droplets were noted within Leydig cells at this period. From 121-150 days of age serum testosterone was lower in BB (1.38 +/- .23 vs. 3.42 +/- .45 vs. 2.94 +/- .81 ng/ml; P less than .05) than controls or semi-starved rats. Serum LH was not significantly higher in controls than in BB rats (63.2 +/- 7.4 vs. 36.6 +/- 12 ng/ml; P = NS). Between 151-200 days of age, there was further lipid accumulation in Leydig cells in the BB rat and occasional epithelial disorganization. After 200 days, serum testosterone decreased (P less than .05) to similar levels in both control and BB rats (1.42 +/- .87 vs. 1.22 +/- .25; P = NS) and was similar in BB rats after 250 days (1.02 +/- .2 ng/ml). After 250 days of age Leydig cell morphology appeared relatively normal but marked alterations were apparent in Sertoli cells, germ cells and morphology of the tubule wall.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum lipids and lipoprotein composition in spontaneously diabetic BB Wistar rats

Serum lipid and lipoprotein composition in spontaneously diabetic BB Wistar rats, nondiabetic littermates, and control Wistar rats was studied to elucidate diabetes-related abnormalities of lipoprotein composition. Serum total triglycerides and pre-beta-lipoprotein concentrations of insulin-treated spontaneously diabetic BB and nondiabetic littermate rats were significantly higher than those of control Wistar rats. Serum cholesterol and HDL cholesterol concentrations of spontaneously diabetic BB and nondiabetic littermate rats did not differ from controls. Concentrations of very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL) of spontaneously diabetic BB and nondiabetic littermate rats were higher than those of normal rats. With sodium dodecylsulfate-polyacrylamide gel electrophoresis it was observed that the spontaneously diabetic BB and nondiabetic littermate rat VLDL contained higher percentages of apoE relative to total apoC when compared with control Wistar rats. With isoelectric focusing, apoC-II relative percentages in VLDL and HDL of both spontaneously diabetic BB and nondiabetic littermate rats were higher than apoC-II proportions in VLDL and HDL of controls. Apolipoprotein A-I of the control rat HDL showed four isoforms that focused at pI 5.8 (17.3%), 5.75 (30.6%), 5.65 (31.8%), and 5.55 (20.5%); however, the spontaneously diabetic BB and nondiabetic littermate rat HDL apoA-I was mainly represented by two isoforms that focused at pI 5.8 and 5.75. VLDL of both diabetic and nondiabetic BB rats contained higher levels of acidic apoE isoforms compared to their counterparts in control Wistar rats. Although HDL cholesterol concentrations of spontaneously diabetic BB rats remained normal, protein concentrations were higher resulting in a low cholesterol/protein ratio in HDL suggesting that the cholesterol-carrying capacity of spontaneously diabetic BB rat HDL could be less than normal and may be due to an abnormal apoA-I composition. Quantitative alterations of lipid and lipoprotein composition appear in the BB Wistar rat when compared to the Wistar rat, but some of the changes are more pronounced in the spontaneously diabetic BB Wistar rat.     

Phenotypic selection: a successful strategy to fix major genes of hypertension

Spontaneously diabetic BB/OK rats are not genetically susceptible to develop diabetic complications as hypertension or nephropathy. Recently, we generated 5 congenic BB. SHR rat strains by transferring different chromosomal regions of the spontaneously hypertensive rat (SHR) onto the genetic background of BB/OK rats. Four out of 5 strains showed a weak increase of blood pressure (8 mmHg). This weak blood pressure effect indicated that the transferred regions fo not contain major genes for hypertension. That prompted us to choose the classical procedure of phenotypic selection to fix major genes causing hypertension in a BB/OK rat subline generated by cross of BB/OK and SHR and repeated backcrossing of animals with highest blood pressure onto normotensive BB/OK rats. After 7 backcrosses (N8), all backcross parents were genetically analysed with the aid of 259 microsatellites to identify loci causing blood pressure of 177 ± 10 mmHg in this BB/OK rat subline. The data revealed, that loci on chromosome 1, 14 and 18 were heterozygous until BC5, BC6 and BC7, respectively. Considering the relative stable high blood pressure during the backcross procedure, these loci might be of essential importance for the development of hypertension in the SHR.     

Assessment of the antidiabetic activity of epicatechin in streptozotocin-diabetic and spontaneously diabetic BB/E rats

(–)-Epicatechin has previously been suggested to rapidly reverse alloxan diabetes in rats. We have assessed the therapeutic value of the compound in two further animal models of insulin-dependent diabetes mellitus, namely streptozotocin - diabetic rats and the spontaneously diabetic BB/E rat . There was no indication of a reversal of established diabetes in either the streptozotocin-diabetic or the spontaneously diabetic BB/E rats. Moreover, epicatechin also failed to halt the progression of the disease in prediabetic BB/E rats. Earlier claims of the potential use of epicatechin as an antidiabetic agent must therefore be treated with some caution.     

Phenotypic selection: a successful strategy to fix major genes of hypertension.

Hypertension is dominantly inherited in cross hybrids between hypertensive SHR/Mol and normotensive BB/OK rats. We used these cross hybrids for repeated backcrossing of selected hypertensive animals onto normotensive BB/OK rats to fix high blood pressure and to generate a hypertensive and diabetic BB/OK rat subline. After 8 backcrosses, the backcross parents were genetically analysed with the aid of 259 microsatellite markers to identify SHR genes causing blood pressure of 177 +/- 10 mmHg in this BB/OK rat subline. Loci on chromosomes 1, 14 and 18 showed longest heterozygosity. These loci might contain major genes of the SHR rat causing hypertension in this BB/OK rat subline. This classical strategy seems to be most suitable to fix major genes of hypertension in particular and complex traits in general and therefore to generate new animal models.     

Free radical activity during development of insulin-dependent diabetes mellitus in the rat.

Free radical-induced lipid peroxidation was quantified by measuring expired pentane from diabetic prone BB Wistar rats of 45-90 d of age. Insulin-dependent diabetes mellitus was manifest at the age of 71 +/- 8 d. Expired pentane increased from 2.1 +/- 0.7 to 5.0 +/- 3.0 pmol/100g/min (p less than 0.01) at manifestation of the disease and remained high throughout the test period. In healthy age-matched control rats it persisted low. In rats made diabetic with streptozotocin, expired pentane remained low. The changes in expired pentane suggest that the development of endogenous insulin-dependent diabetes mellitus in BB rats is associated with increased free radical activity. This is not due to hyperglycemia or ketosis per se, and reflects a fundamental difference in the free radical activity between the spontaneously diabetic BB rats and the disease produced by streptozotocin. Development of spontaneous insulin-dependent diabetes in BB rats is associated with increased free radical activity that persists after the manifestation of the disease.     

Congenic diabetes-prone BB.Sa and BB.Xs rats differ from their progenitor strain BB/OK in frequency and severity of insulin-dependent diabetes mellitus.

Two newly established congenic diabetes-prone BB rat strains designated BB.Sa and BB.Xs carrying a region of chromosome 1 (Sa-Lsn-Secr-Igf2-Tnt, 16 cM) and a region of chromosome X (DXMgh3-Mycs/Pfkb1-Ar, 36 cM) of the SHR rats, respectively, were studied to determine whether the transferred chromosomal regions influence diabetes frequency, age at onset, and clinical picture. Therefore, 4 complete litters of BB/OK (n = 43), BB.Sa (n = 45), and BB.Xs (n = 41) were observed for diabetes occurrence up to the age of 30 weeks. From these litters 6 diabetic males of each strain manifesting in an interval of 1 week were chosen to study body weight, blood glucose, insulin requirement to survive, and several diabetes-related serum constituents at onset of diabetes and after a diabetes duration of 150 days. The diabetes frequency was significantly lower in BB.Xs than in rats of the parental strain BB/OK, whereas comparable frequencies were found between BB/OK and BB.Sa rats. Obvious differences were observed 150 days after diabetes onset between BB/OK and both BB.Sa and BB.Xs rats. BB/OK rats were significantly heavier and needed significantly more insulin/100 g body weight than BB.Sa and BB.Xs rats. Comparisons of the serum constituents as lipids, proteins, and minerals revealed significant differences between diabetic BB/OK rats and their diabetic congenic derivatives in several traits studied at onset and after 150 days of insulin treatment. These results not only show the power of congenic lines in diabetes research, but indicate for the first time that there are genetic factors on chromosomes 1 and X influencing frequency and severity of diabetes in the BB/OK rat.     

Genes of SHR rats protect spontaneously diabetic BB/OK rats from diabetes: lessons from congenic BB.SHR rat strains

Diabetes in BB rats share many common features with human type 1 diabetes. One of them is the complex and polygenic nature of disease. Analysis of cross hybrids of diabetic BB/OK rats and rats of different diabetes-resistant strains has demonstrated that beside the MHC genes, Iddm1 and the lymphopenia, Iddm2, additional non-MHC genes are involved in diabetes development. To study the importance of the non-MHC genes, Iddm4 and Iddm3, two congenic BB.SHR rat strains were generated by recombining a segment of the SHR chromosome 6 (Iddm4; termed BB.6S; 15cM) or chromosome 18 (Iddm3; termed BB.18S; 24cM) into the BB/OK background by serial backcrossing and marker-aided selection. The characterization of both congenic strains demonstrates a drastic reduction of diabetes frequency in comparison to the BB/OK strain (86% vs 14% and 34%). It is supposed that diabetes protective genes of SHR must be located on both chromosomal segments and that these suppress the action of the essential and most important genes of diabetes development in the BB/OK rat, Iddm1, and Iddm2.     

Lipoperoxidation in hepatic subcellular compartments of diabetic rats

It is known that an accumulation of lipoperoxidative aldehydes malondialdehyde (MDA) and 4-hydroxynonenal (HNE) takes place in liver mitochondria during aging. The existence and role of an increased extra- and intra-cellular oxidative stress in diabetes, an aging-accelerating disease, is currently under discussion. This report offers evidence that lipoperoxidative aldehydes accumulate in liver microsomes and mitochondria at a higher rate in spontaneously diabetic BB/WOR rats than in control non-diabetic animals (HNE content, diabetes vs. control: microsomes 80.6+/-19.9 vs. 25.75+/-3.6 pmol/mg prot, p = .024; mitochondria 77.4+/-15.4 vs. 26.5+/-3.5 pmol/mg prot, p = .0103). Liver subcellular fractions from diabetic rats, when exposed to the peroxidative stimulus ADP/Fe, developed more lipoperoxidative aldehydes than those from non diabetic rats (HNE amount, diabetes vs. control: microsomes 3.60+/-0.37 vs. 2.33+/-0.22 nmol/mg prot, p = .014; mitochondria 3.62+/-0.26 vs. 2.30+/-0.17 nmol/mg prot, p = .0009). Liver subcellular fractions of diabetic rats developed more fluorescent chromolipids related to HNE-phospholipid adducts, either after in vitro peroxidation (microsomes: p = .0045; mitochondria: p = .0023) or by exposure to exogenous HNE (microsomes: p = .049; mitochondria: p = .0338). This higher susceptibility of diabetic liver membranes to the non-enzymatic attack of HNE may be due to an altered phospholipid composition. Moreover, a decreased activity of the HNE-metabolizing systems can be involved: diabetic liver mitochondria and microsomes were unable to consume exogenous HNE at the same rate as non-diabetic membranes; the difference was already significant after 5' incubation (microsomes p<.001; mitochondria p<.001). These data show an increased oxidative stress inside the hepatocytes of diabetic rats; the impairment of the HNE-metabolizing systems can play a key role in the maintenance and propagation of the damage.     

Serum metabolite signature predicts the acute onset of diabetes in spontaneously diabetic congenic BB rats

The clinical presentation of type 1 diabetes is preceded by a prodrome of beta cell autoimmunity. We probed the short period of subtle metabolic abnormalities, which precede the acute onset of diabetes in the spontaneously diabetic BB rat, by analyzing the serum metabolite profile detected with combined gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS). We found that the metabolite pattern prior to diabetes included 17 metabolites, which differed between individual diabetes prone (DP) BB rats and their age and sex matched diabetes resistant (DR) littermates. As the metabolite signature at the 40?days of age baseline failed to distinguish DP from DR, there was a brief 10-day period after which the diabetes prediction pattern was observed, that includes fatty acids (e.g. oleamide), phospholipids (e.g. phosphocholines) and amino acids (e.g. isoleucine). It is concluded that distinct changes in the serum metabolite pattern predict type 1 diabetes and precede the appearance of insulitis in spontaneously diabetic BB DP rats. This observation should prove useful to dissect mechanisms of type 1 diabetes.     

Increased plasma and tissue levels of vitamin E in the spontaneously diabetic BB rat

Increased plasma and tissue levels of vitamin E were found in spontaneously diabetic BB rats (D) as well as asymptomatic/diabetes-prone BB rats (AD) in comparison to levels in non-diabetic control rats (ND). Treatment of D rats with insulin for 30 days returned plasma and tissue values of vitamin E to control levels. The changes reported here could not be explained solely on the basis of variations in total lipid content of plasma. These data suggest the metabolism of vitamin E is altered in asymptomatic and spontaneously diabetic BB rats and this alteration returns to control values following insulin treatment. Furthermore, it might be speculated that these data indicate a relationship between vitamin E and insulin.     

Cardiac dysfunction in isolated perfused hearts from spontaneously diabetic BB rats

The purpose of this investigation was to examine cardiac function and biochemistry in spontaneously diabetic BB rats, a strain in which diabetes occurs spontaneously and closely resembles insulin-dependent diabetes in humans. The study involved two groups: nondiabetic littermates of BB rats and BB diabetic rats treated daily with a very low insulin dose such that the rats were severely hyperglycemic and hyperlipidemic. The hearts from these two groups were isolated and heart function (using isolated perfused working hearts) and biochemistry were examined 6 weeks after the onset of diabetes. BB diabetic rats exhibited a lower calcium-stimulated myosin ATPase activity and depressed left ventricular developed pressure, cardiac contractility, and ventricular relaxation rates compared with BB nondiabetic littermates. These results suggest that the chronically diabetic state in the BB rat produces cardiac changes similar to those demonstrable after chemical diabetes induced by alloxan or STZ, or that seen during human diabetes mellitus.     

Endothelins urinary excretion is increased in spontaneously diabetic rats: BB/BB

Previously we reported (1) an increase of endothelin-1,2 (ET) content, in urine of rats made diabetic with streptozotocin (STZ), starting three days and up to 20 weeks from diabetes induction. The increased ET excretion was considered as an early marker of endothelial damage. To ascertain if this phenomenon was present also in a strain of spontaneously diabetic rats, endothelin-1,2 urinary excretion was determined in BB/BB diabetic rats, and their control (BB/WB), at different times after the onset of diabetes, (two, four, six and twelve weeks). BB/BB diabetic rats showed elevated urinary excretion of endothelins as compared to BB/WB control rats, starting two weeks after diabetes onset, and up to twelve weeks. In the same animals, Nerve Conduction Velocity (NCV), was monitored at the same time as an index of the occurrence of a diabetes complication (peripheral neuropathy). NCV resulted to be impaired in the BB/BB diabetic rats as compared to control rats; however the increase of ET in urine, is earlier in comparison to peripheral neuropathy. These data suggest the hypothesis that endothelial damages preceed the overt manifestations of peripheral neuropathy associated to diabetes.     

Hormone levels and antler development in white-tailed and sika fawns

Overall mean values of testosterone (T), androstenedione (A), thyroxine (T4), calcium (Ca), phosphorus (P), and alkaline phosphatase (AP) were (T) 2.56 +/- 2.44 ng/ml, (A) 3.16 +/- 2.58 ng/ml, (T4) 8.22 +/- 4.18 micrograms/dl, (Ca), 10.88 +/- 0.65 mg%, (P) 8.03 +/- 0.68 mg%, and (AP) 81.89 +/- 19.45 IU/l in white-tailed fawns and (T) 3.69 +/- 2.76 ng/ml, (A) 18.26 +/- 17.58 ng/ml, (T4) 4.41 +/- 1.59 micrograms/dl, (Ca) 10.08 +/- 0.80 mg%, (P) 9.42 +/- 1.69 mg% and (AP) 95.35 +/- 22.65 IU/l in sika fawns. High T titers correlated with antler button growth, and A titers peaked as buttons hardened in both groups. Higher T4 levels in late fall and early winter may have had a synergistic role for button growth in both groups. Generally higher P levels in sika fawns and relatively higher Ca levels in white-tailed fawns might be species dependent. However, relatively constant Ca and P in both groups represented mineral homeostasis. The mineralization role of AP activity was evident in both groups.     

Infant formula ingestion is associated with the development of diabetes in the BB/Wor rat

The association between early exposure to cow's milk products in infancy and risk for insulin dependent diabetes mellitus (IDDM) is controversial. We examined whether the ingestion of cow's milk-based infant formula altered the expression of the diabetic syndrome in the BB/Wor rat, an animal model of IDDM. Pregnant BB/Wor dams were obtained from the NIH contract colony at the University of Massachusetts and housed under semi-barrier conditions. Rat pups were intubated with 1 to 2 ml of commercially available cow's milk-based infant formula (Enfamil or Nutramigen) or sham intubated (controls) daily from day 12 to day 25 of life. Pups were weaned at day 25 and monitored for glucosuria daily through 120 days of life. All rats including dams consumed a milk-free rat chow and acidified water ad libitum throughout the study. The mean age of disease onset was 4 to 10 days earlier in Nutramigen-fed and Enfamil-fed rats relative to controls (84+/-3, 78+/-2 and 88+/-4 days, respectively); the mean age of disease onset was significantly different between controls and Enfamil-fed animals (p<0.05). At 120 days, 60% (12/20) of control rats developed diabetes versus 100% of animals fed either type of infant formula prior to weaning (15/15:Enfamil-fed; 19/19:Nutramigen-fed) (p<0.05). These data indicate that direct, early ingestion of cow's milk-based formula was related to the expression of diabetes in the BB/Wor rat.     

Hepatic microsomal delta 9 desaturation of stearic acid in the spontaneously diabetic female BB rat

delta 9 desaturation of stearic (1-14C) acid has been estimated from incubation of liver microsomes of adult female spontaneously diabetic BB rat, an animal model resembling the spontaneous juvenile diabetes in humans, comparatively to adult female control Wistar rat. The animals were sacrificed, when hyperglycemic, 24 hours after the last insulin injection to the BB rats. Stearic acid delta 9 desaturase activity is drastically depressed in the BB rats when fatty acid composition of liver phospholipids and microsomal total liver lipids are changed in spite of the daily injection of insulin necessary for the BB rats survival.     

Cardiovascular autonomic neuropathy in spontaneously diabetic rats with and without application of EGb 761

Cardiovascular autonomic neuropathy causes abnormalities in the diabetic heart with various clinical sequelae, including exercise intolerance, arrhythmias and painless myocardial infarction. Little is known about (ultra)structural alterations of the myocardial nervous network. On the assumption that this diabetes-specific neuropathy develops due to permanently increased oxidative stress by liberation of oxygen-free radicals, adjuvant application of antioxidative therapeutics appears promising in preventing or delaying long-term diabetic complications. We have investigated the effects of Ginkgo biloba extract (EGb 761), a radical scavenger, against diabetes-induced myocardial nervous damage in spontaneously diabetic BioBreeding/Ottawa Karlsburg (BB/OK) rats. Morphological and morphometric parameters were evaluated by electron microscopy. We used immunohistochemistry to investigate protein expression of protein gene product 9.5, S100 protein, and thyroxin hydroxylase as a neuronal marker. Alterations of cardiac sympathetic activity were measured using the in vivo 123I-metaiodobenzyl-guanidine imaging, and the immunofluorescent labeling of beta1-adrenergic receptors and adenylate cyclase. Our results revealed that A) Diabetes results in slight to moderate ultrastructural alterations (hydrops, disintegration of substructure) of autonomic nerve fibers and related Schwann cells in untreated BB diabetic rats; B) Cardiac sympathetic integrity and activity is impaired due to alterations in the presynaptic nerve terminals and the postsynaptic ?1-AR-AC coupling system; C) Pre-treatment of diabetic myocardium with EGb results in an improvement of most of these parameters compared to unprotected myocardium. In conclusion, EGb may act as a potent therapeutic adjuvant in diabetics with respect to cardiovascular autonomic neuropathy, which may contribute to the prevention of late complications in diabetes.     

Altered cardiac excitation-contraction coupling in ventricular myocytes from spontaneously diabetic BB rats

Cardiac excitation-contraction (E-C) coupling abnormalities in chemically induced diabetes have been well defined. Heart dysfunction has also been reported in diabetes of genetic origin. The purpose of this study was to determine whether heart dysfunction in genetically predisposed diabetes is attributable to impaired E-C coupling at the cellular level. Myocytes were isolated from 1-yr-old BioBreed (BB) spontaneously diabetic-prone (BB/DP) rats and their diabetic-resistant littermates (BB/DR). Mechanical properties were evaluated by use of a video edge-detection system. Myocytes were electrically stimulated at 0.5 Hz. The contractile properties analyzed included peak shortening (PS), time-to-peak shortening (TPS), time-to-90% relengthening (TR(90)), and maximal velocities of shortening and relengthening (+/-dL/dt). Intracellular Ca(2+) handling was evaluated with fura 2 fluorescent dye. Myocytes from spontaneously diabetic hearts exhibited a depressed PS, prolonged TPS and TR(90), and reduced +/-dL/dt. Consistent with the mechanical response, myocytes from the BB/DP group displayed reduced resting and peak intracellular Ca(2+) concentration associated with a slowed Ca(2+)-transient decay. Furthermore, myocytes from BB/DP hearts were less responsive to increases in extracellular Ca(2+) and norepinephrine and equally responsive to increases in stimulation frequency and KCl compared with those from the BB/DR group. These results suggest that the genetic diabetic state produces altered cardiac E-C coupling, in part, because of abnormalities of the myocyte, similar to that demonstrable after chemically induced diabetes or during human diabetes.     

Epidermal growth factor excretion and receptor binding in diabetic rats

Urinary epidermal growth factor (EGF) excretion was calculated as ng EGF per mg creatinine and ng EGF per 24 hr. It was increased 4-9 fold in rats with genetic (BB) or streptozotocin-induced diabetes. It decreased to 2-3 fold control values in insulin-treated animals. In contrast, EGF concentration in serum was lower in diabetic than in control rats (360 +/- 72 vs 524 +/- 150 pg/ml, P .086); EGF level in plasma was unchanged (319 +/- 67 vs 313 +/- 96 pg/ml). In diabetic rats EGF content was increased in submaxillary glands (1018 +/- 259 vs 738 +/- 122 pg/mg protein, P .060) but unchanged in the kidneys (70 +/- 18 vs 65 +/- 6 pg/mg protein in controls). EGF binding to the liver microsomes in diabetic rats was decreased by 30-40% and was not restored by insulin therapy. Binding to the kidneys also showed a tendency to decrease in diabetic animals. The EGF excretion and receptor binding were normal in obese normoglycemic Zucker fa/fa rats. We suggest that hyperglycemia and/or glucosuria may affect EGF synthesis and/or excretion in the kidneys and EGF synthesis or accumulation in the megakaryocytes. The mechanism of decreased EGF receptor binding remains to be clarified.