Mo Of Diabetes Research Articles

Inhibition of JNK by novel curcumin analog C66 prevents diabetic cardiomyopathy with a preservation of cardiac metallothionein expression

The development of diabetic cardiomyopathy is attributed to diabetic oxidative stress, which may be related to the mitogen-activated protein kinase (MAPK) c-Jun NH2-terminal kinase (JNK) activation. The present study tested a hypothesis whether the curcumin analog C66 [(2E,6E)-2,6-bis(2-(trifluoromethyl)benzylidene) cyclohexanone] as a potent antioxidant can protect diabetes-induced cardiac functional and pathogenic changes via inhibition of JNK function. Diabetes was induced with a single intraperitoneal injection of streptozotocin in male C57BL/6 mice. Diabetic and age-matched control mice were randomly divided into three groups, each group treated with C66, JNK inhibitor (JNKi, SP600125), or vehicle (1% CMC-Na solution) by gavage at 5 mg/kg every other day for 3 mo. Neither C66 nor JNKi impacted diabetic hyperglycemia and inhibition of body-weight gain, but both significantly prevented diabetes-induced JNK phosphorylation in the heart. Compared with basal line, cardiac function was significantly decreased in diabetic mice at 3 mo of diabetes but not in C66- or JNKi-treated diabetic mice. Cardiac fibrosis, oxidative damage, endoplasmic reticulum stress, and cell apoptosis, examined by Sirius red staining, Western blot, and thiobarbituric acid assay, were also significantly increased in diabetic mice, all which were prevented by C66 or JNKi treatment under diabetic conditions. Cardiac metallothionein expression was significantly decreased in diabetic mice but was almost normal in C66- or JNKi-treated diabetic mice. These results suggest that, like JNKi, C66 is able to prevent diabetic upregulation of JNK function, resulting in a prevention of diabetes-induced cardiac fibrosis, oxidative stress, endoplasmic reticulum stress, and cell death, along with a preservation of cardiac metallothionein expression.

Evidence for Diffuse Central Retinal Edema In Vivo in Diabetic Male Sprague Dawley Rats

BackgroundInvestigations into the mechanism of diffuse retinal edema in diabetic subjects have been limited by a lack of animal models and techniques that co-localized retinal thickness and hydration in vivo. In this study we test the hypothesis that a previously reported supernormal central retinal thickness on MRI measured in experimental diabetic retinopathy in vivo represents a persistent and diffuse edema.Methodology/Principal FindingsIn diabetic and age-matched control rats, and in rats experiencing dilutional hyponatremia (as a positive edema control), whole central retinal thickness, intraretinal water content and apparent diffusion coefficients (ADC, ‘water mobility’) were measured in vivo using quantitative MRI methods. Glycated hemoglobin and retinal thickness ex vivo (histology) were also measured in control and diabetic groups. In the dilutional hyponatremia model, central retinal thickness and water content were supernormal by quantitative MRI, and intraretinal water mobility profiles changed in a manner consistent with intracellular edema. Groups of diabetic (2, 3, 4, 6, and 9 mo of diabetes), and age-matched controls were then investigated with MRI and all diabetic rats showed supernormal whole central retinal thickness. In a separate study in 4 mo diabetic rats (and controls), MRI retinal thickness and water content metrics were significantly greater than normal, and ADC was subnormal in the outer retina; the increase in retinal thickness was not detected histologically on sections of fixed and dehydrated retinas from these rats.Conclusions/SignificanceDiabetic male Sprague Dawley rats demonstrate a persistent and diffuse retinal edema in vivo, providing, for the first time, an important model for investigating its pathogenesis and treatment. These studies also validate MRI as a powerful approach for investigating mechanisms of diabetic retinal edema in future experimental and clinical investigations.

Transmural differences in respiratory capacity across the rat left ventricle in health, aging, and streptozotocin-induced diabetes mellitus: evidence that mitochondrial dysfunction begins in the subepicardium

In diabetic cardiomyopathy, ventricular dysfunction occurs in the absence of hypertension or atherosclerosis and is accompanied by altered myocardial substrate utilization and depressed mitochondrial respiration. It is not known if mitochondrial function differs across the left ventricular (LV) wall in diabetes. In the healthy heart, the inner subendocardial region demonstrates higher rates of blood flow, oxygen consumption, and ATP turnover compared with the outer subepicardial region, but published transmural respirometric measurements have not demonstrated differences. We aim to measure mitochondrial function in Wistar rat LV to determine the effects of age, streptozotocin-diabetes, and LV layer. High-resolution respirometry measured indexes of respiration in saponin-skinned fibers dissected from the LV subendocardium and subepicardium of 3-mo-old rats after 1 mo of streptozotocin-induced diabetes and 4-mo-old rats following 2 mo of diabetes. Heart rate and heartbeat duration were measured under isoflurane-anesthesia using a fetal-Doppler, and transmission electron microscopy was employed to observe ultrastructural differences. Heart rate decreased with age and diabetes, whereas heartbeat duration increased with diabetes. While there were no transmural respirational differences in young healthy rat hearts, both myocardial layers showed a respiratory depression with age (30-40%). In 1-mo diabetic rat hearts only subepicardial respiration was depressed, whereas after 2 mo diabetes, respiration in subendocardial and subepicardial layers was depressed and showed elevated leak (state 2) respiration. These data provide evidence that mitochondrial dysfunction is first detectable in the subepicardium of diabetic rat LV, whereas there are measureable changes in LV mitochondria after only 4 mo of aging.

Kidney expression of glutathione peroxidase-1 is not protective against streptozotocin-induced diabetic nephropathy

In many diseases, including progressive renal disorders, tissue injury and pathological intracellular signaling events are dependent on oxidative stress. Glutathione peroxidase-1 (Gpx1) is an antioxidant enzyme that is highly expressed in the kidney and removes peroxides and peroxynitrite that can cause renal damage. Therefore, we examined whether this abundant renal antioxidant enzyme limits renal damage during the development of type 1 diabetic nephropathy. Wild-type (Gpx1+/+) and deficient (Gpx1-/-) mice were made diabetic by intraperitoneal injection of streptozotocin (100 mg/kg) on 2 consecutive days. Diabetic Gpx1+/+ and -/- mice with equivalent blood glucose levels (23 +/- 4 mM) were selected and examined after 4 mo of diabetes. Compared with normal mice, diabetic Gpx1+/+ and -/- mice had a two- to threefold increase in urine albumin excretion at 2 and 4 mo of diabetes. At 4 mo, diabetic Gpx1+/+ and -/- mice had equivalent levels of oxidative renal injury (increased kidney reactive oxygen species, kidney lipid peroxidation, urine isoprostanes, kidney deposition of advanced glycoxidation, and nitrosylation end products) and a similar degree of glomerular damage (hypertrophy, hypercellularity, sclerosis), tubular injury (apoptosis and vimentin expression), and renal fibrosis (myofibroblasts, collagen, TGF-beta excretion). A lack of Gpx1 was not compensated for by increased levels of catalase or other Gpx isoforms in diabetic kidneys. Contrary to expectations, this study showed that the high level of Gpx1 expressed in the kidney is not protective against the development of renal oxidative stress and nephropathy in a model of type 1 diabetes.

Differential activation of NF-kappa B and AP-1 in increased fibronectin synthesis in target organs of diabetic complications.

Increased extracellular matrix protein production leading to structural abnormalities is a characteristic feature of chronic diabetic complications. We previously showed that high glucose in endothelial cell culture leads to the upregulation of basement membrane protein fibronectin (FN) via an endothelin (ET)-dependent pathway involving activation of NF-kappaB and activating protein-1 (AP-1). To delineate the mechanisms of basement membrane thickening, we used an animal model of chronic diabetes and evaluated ET-dependent activation of NF-kappaB and AP-1 and subsequent upregulation of FN in three target organs of chronic diabetic complications. After 3 mo of diabetes, retina, renal cortex, and myocardium demonstrated increased FN mRNA and increased ET-1 mRNA expression. Increased FN expression was shown to be dependent on ET receptor-mediated signaling, as the increase was prevented by the dual ET receptor antagonist bosentan. NF-kappaB activation was most pronounced in the retina, followed by kidney and heart. AP-1 activation was also most pronounced in the retina but was similar in both kidney and heart. Bosentan treatment prevented NF-kappaB activation in the retina and heart and AP-1 activation in the retina and kidney. These data indicate that, although ETs are important in increased FN production due to diabetes, the mechanisms with respect to transcription factor activation may vary depending on the microenvironment of the organ.

Alpha-lipoic acid attenuates hyperglycemia and prevents glomerular mesangial matrix expansion in diabetes.

Previous studies demonstrated that 2 mo of dietary supplementation with alpha-lipoic acid (LA) prevented early glomerular injury in non-insulin-treated streptozotocin diabetic rats (D). The present study examined the effects of chronic LA supplementation (30 mg/kg body wt per d) on nephropathy in D after 7 mo of diabetes. Compared with control rats, D developed increased urinary excretion of albumin and transforming growth factor beta, renal insufficiency, glomerular mesangial matrix expansion, and glomerulosclerosis in association with depletion of glutathione and accumulation of malondialdehyde in renal cortex. LA prevented or ameliorated all of these changes in D. Because chronic LA supplementation also attenuated hyperglycemia in D after 3 mo, its effects on renal injury were compared with treatment of rats with sufficient insulin to maintain a level of glycemic control for the entire 7-mo period (D-INS) equivalent to that observed with LA during the final 4 mo. Despite superior longitudinal glycemic control in D-INS, urinary excretion of albumin and transforming growth factor beta, glomerular mesangial matrix expansion, the extent of glomerulosclerosis, and renal cortical malondialdehyde content were all significantly greater, whereas cortical glutathione content was lower than corresponding values in D given LA. Thus, the renoprotective effects of LA in D were not attributable to improved glycemic control alone but also likely reflected its antioxidant activity. The combined antioxidant and hypoglycemic actions of LA both may contribute to its utility in preventing renal injury and other complications of diabetes.

C‐Peptide Deficiency: An Important Pathogenetic Factor In Type 1 Diabetic Neuropathy

Background: C‐peptide has insulin‐like effects and ameliorates the acute nerve conduction defect (NCD) in experimental and human type 1 diabetic neuropathy (DN). Methods: In this study, diabetic BB/Wor‐rats were treated with rat C‐peptide (75 ng/kg) from onset of diabetes for 8 months (prevention‐group, PG). In a separate experiment, 5‐mo untreated diabetic BB/Wor‐rats were started on the same C‐peptide treatment continued to 8 mo of diabetes (intervention group, IG). Results: In the PG, the NCD was significantly decreased (p < 0.001) compared to untreated BB/Wor‐rats and was similar to that of normo‐C‐peptidemic and isohyperglycemic type 2 BBZ rats. This effect was associated with significant preventions of nodal changes (p < 0.001) including axo‐glial dysjunction (p < 0.001), which was not different from non‐diabetic control rats. Axonal atrophy and Wallerian degeneration were significantly prevented (both p < 0.05). In the IG, the NCD decreased significantly (p < 0.01) during the 3 mo treatment period. Associated with the functional improvement, nodal changes improved significantly (p < 0.001) as did axonal degenerative changes (p < 0.01). C‐peptide treatment in the IG resulted in a significant increase in the frequency of regenerating fibers (p < 0.001) compared with untreated 5 mo diabetic rats. Conclusion: These studies demonstrate that C‐peptide replacement in type 1 diabetes prevents the chronic NCD and structural changes. Furthermore, C‐peptide treatment significantly improves the already established functional and structural abnormalities of DN. This is the first demonstration of a therapeutic improvement of established neuropathy in experimental diabetes. We conclude that C‐peptide deficiency in type 1 diabetes is an important pathogenetic component of DN and that its replacement may provide a valuable adjunct to intensive insulin treatment.

Regulation of renal laminin in mice with type II diabetes.

This study examines the regulation of renal laminin in the db/db mouse, a model of type II diabetes characterized by extensive remodeling of extracellular matrix. Immunohistochemistry demonstrated an increase in the contents of laminin chains including beta1 chain in the mesangium and tubular basement membranes at 1, 2, 3, and 4 mo of diabetes. Immunofluorescence with an antibody against the recently discovered laminin alpha5 chain showed that in the normal mouse, the protein had a restricted distribution to the glomerular and tubular basement membranes with scant expression in the mesangium of older mice. In the diabetic mouse, the laminin alpha5 chain content of the glomerular and tubular basement membranes was increased, with marked expression in the mesangium. Northern analysis revealed a significant decrease in the renal cortical contents of alpha5, beta1, and gamma1 chain mRNA in the diabetic mice compared to control, at each of the time points. In situ hybridization showed decreased abundance of alpha5 transcripts in the glomeruli of diabetic mice compared to nondiabetic controls. Analysis of mRNA changes by Northern and in situ hybridization studies demonstrated that the reduction in laminin transcripts involved both glomerular and tubular elements. These observations demonstrate that laminin accumulation in the db/db mice with type II diabetes is due to nontranscriptional mechanisms. Because previous investigations in rodents with type I diabetes have shown that the increase in renal laminin content was associated with a corresponding increment in laminin chain transcript levels, it appears that the mechanisms underlying augmentation in renal matrix laminin content may be distinct in the two types of diabetes.

Effect of GH/IGF-I deficiency on long-term renal changes and urinary albumin excretion in diabetic dwarf rats.

Growth hormone (GH) and insulin-like growth factor I (IGF-I) may play a role in early diabetic renal and glomerular growth and in the later development of experimental diabetic kidney disease. Rats from a genetic GH/IGF-I-deficient dwarf rat strain were made streptozotocin diabetic and were compared with nondiabetic dwarf rats. GH/IGF-I-intact rats with and without diabetes served as controls. After 6 mo of diabetes, kidney weight and total glomerular volume increased significantly in GH/IGF-I-intact diabetic rats compared with the nondiabetic GH/IGF-I-intact rats (P < 0.05), whereas the diabetic dwarf rats had insignificant changes compared with dwarf control rats. By the end of the study, urinary albumin excretion (UAE) increased from similar base levels of approximately 15-20 micrograms/24 h to 473 +/- 52 (SE) micrograms/24 h in GH/IGF-I-intact diabetic rats compared with 151 +/- 32 micrograms/24 h in diabetic dwarf rats (P < 0.01). In conclusion, isolated GH/IGF-I deficiency reduces the degree of renal and glomerular hypertrophy and the increase in UAE after 6 mo of experimental diabetes in GH/IGF-I-deficient rats.

Nerve function and regeneration in diabetic rats: effects of ZD-7155, an AT1 receptor antagonist.

Effects of the angiotensin II AT1 receptor antagonist ZD-7155 on nerve function, blood flow, capillarization, oxygenation, and regenerative capacity after injury were studied in streptozocin-diabetic rats. Deficits in saphenous sensory and sciatic motor conduction velocity measured after 1 or 2 mo of diabetes in anesthetized rats were prevented and corrected by ZD-7155. Sciatic resistance to hypoxic conduction failure, which was increased by 71% by 2 mo of diabetes, was attenuated by 39% with ZD-7155. Endoneurial capillary density, which was unaffected by diabetes, was increased by 34% with 2 mo of ZD-7155 treatment. Sciatic nutritive endoneurial blood flow, which was reduced by 45% by 2 mo of diabetes, remained in the nondiabetic range with ZD-7155. Mean endoneurial O2 tension was reduced 38% by diabetes, which was attenuated by ZD-7155. Punctate freeze damage of sciatic nerve caused complete fiber degeneration. Fourteen days postlesion, there was a 26% deficit in myelinated fiber regeneration distance after 2 mo of diabetes, which was prevented by ZD-7155 treatment from diabetes induction. Thus alterations in the renin-angiotensin system contribute to the neurovascular etiology of nerve dysfunction in experimental diabetes.

Aldose Reductase Inhibition Fails to Prevent Retinopathy in Diabetic and Galactosemic Dogs

To investigate a possible role of excessive polyol production in the pathogenesis of diabetic retinopathy, 16 ALX-induced diabetic dogs and 20 experimentally galactosemic dogs were randomly assigned to 5 yr of treatment with either sorbinil, an aldose reductase inhibitor, or a placebo. The severity of hyperglycemia in sorbinil-treated and placebo groups was monitored throughout the 5-yr study by assay of glycosuria and nonenzymatically glycated plasma protein and HbA 1 needed in an effort to avoid confounding possible group differences in hyperglycemia severity with possible drug effects. Inhibition of polyol production by sorbinil was monitored in erythrocytes throughout the study and also in retina and other tissue obtained at autopsy. Trypsin digests of retinal vessels were compared after 60 mo of diabetes and after 42 and 60 mo of galactosemia. In diabetic dogs, development of retinopathy was not significantly influenced by a sorbinil dose (20 mg · kg −1 · day −1 ) sufficient to prevent elevation of sorbitol levels in retina and other tissue. Likewise, in dogs made experimentally galactosemic for 42–60 mo, administration of sorbinil (60–80 mg · kg −1 day −1 ) had no significant effect on the development of retinopathy notwithstanding prevention of 93–96% of the polyol elevation in retina and other tissue. Retinal capillary basement membrane was significantly thicker than normal in diabetic and in galactosemic dogs and was not significantly influenced by administration of sorbinil in either dog model. Thus, no evidence was found that the development of retinopathy is critically dependent on excessive polyol production or accumulation.

Amount and Speed of Fast Axonal Transport in Diabetes

Abnormalities in axonal transport have been observed in human and experimental diabetes and may be related to the pathogenesis of diabetic neuropathy. Axonal transport has previously been evaluated by indirect methods. In this study, direct-measurement techniques were applied (with computer-enhanced video-recorded images) for the first time to evaluate intra-axonal organelle speed and frequency (the amount of organelle traffic) in both the anterograde fast component (AFC) and retrograde fast component (RFC) of axonal transport in diabetic nerve. Sciatic nerve and dorsal and ventral nerve roots were studied in the animal model of insulin-dependent diabetes (BB/Wistar rat) and sciatic nerve in the non-insulin-dependent (streptozocin-induced) model of diabetes (STZ-D rat). STZ-D rats were studied at 1 mo, and BB/Wistar rats were studied at 1 and 2 mo of diabetes duration. Statistically significant decreases in peripheral axon organelle speed were found only for RFC at 1 mo of diabetes in both the BB/Wistar (8.1%) and STZ-D (5.4%) rats. The difference was no longer significant in BB/Wistar rats at 2 mo of diabetes. This recovery suggests that the underlying abnormality is reversible. No differences were seen in AFC of any axons, and the only other difference seen was a 5.1% decrement in RFC at 2 mo in the ventral roots. No significant difference was observed in any group for organelle frequencies. Other factors should be considered to explain the decrease in materials transported in accumulation studies. The transient deficits in RFC speed observed remain of undetermined significance in the pathogenesis of diabetic neuropathy.

Sustained hyperglycemia results in testicular dysfunction and reduced fertility potential in BBWOR diabetic rats

Rats with short-term diabetes show a greater than 50% reduction of serum testosterone and increased lipid in Leydig cells but normal testicular structure. The purpose of this study was to determine the extent of testicular pathology (morphology index), integrity of the blood-testis barrier, daily sperm production (DSP), number of Leydig cells per testis (LC/T), and total trunk testosterone (TTT) in diabetic rats (BBWORdp) with long-term hyperglycemia (300-350 mg/dl for greater than 180 days) and to evaluate its effects on fertility potential. Results were compared with similarly aged normoglycemic rats (BBWORdr) and normal control Wistar rats. After 6 mo of diabetes, testis weights, DSPs, TTTs, and the morphology index were significantly reduced. The LC/T was not different from BBWORdr rats. The blood-testis barrier appeared intact, although structural abnormalities were noted in Sertoli-Sertoli junction complexes. There was a significant reduction in the number of pregnancies per rat and implantations per pregnancy in matings utilizing the diabetic BBWORdp rat and control Wistar female rats. Results indicate that long-term diabetes with sustained hyperglycemia leads to significant testicular dysfunction associated with decreased fertility potential.

Modulation of Hemodynamic and Vascular Filtration Changes in Diabetic Rats by Dietary myo-inositol

To assess the potential of myo-inositol-supplemented diets to prevent diabetes-induced vascular functional changes, we examined the effects of diets supplemented with 0.5, 1, or 2% myo-inositol on blood flow and vascular filtration function in nondiabetic control rats and rats with streptozocin-induced diabetes (STZ-D). After 1 mo of diabetes and dietary myo-inositol supplementation, 1) 131I-labeled bovine serum albumin (BSA) permeation of vessels was assessed in multiple tissues, 2) glomerular filtration rate (GFR) was estimated as renal plasma clearance of 57Co-labeled EDTA, 3) regional blood flows were measured with 15-microns 85Sr-labeled microspheres, and 4) endogenous albumin and IgG urinary excretion rates were quantified by radial immunodiffusion assay. In STZ-D rats, 131I-BSA tissue clearance increased significantly (2- to 4-fold) in the anterior uvea, choroid-sclera, retina, sciatic nerve, aorta, new granulation tissue, diaphragm, and kidney but was unchanged in skin, forelimb muscle, and heart. myo-Inositol-supplemented diets reduced diabetes-induced increases in 131I-BSA clearance (in a dose-dependent manner) in all tissues; however, only in new granulation tissue and diaphragm did the 2% myo-inositol diet completely normalize vascular albumin permeation. Diabetes-induced increases in GFR and in urinary albumin and IgG excretion were also substantially reduced or normalized by dietary myo-inositol supplements. Increased blood flow in anterior uvea, choroid-sclera, kidney, new granulation tissue, and skeletal muscle in STZ-D rats also was substantially reduced or normalized by the 2% myo-inositol diet. myo-Inositol had minimal if any effects on the above parameters in control rats. These observations indicate that diabetes-induced increases in regional blood flow, 131I-BSA permeation, GFR, and urinary protein excretion can be markedly reduced or normalized by consumption of myo-inositol-supplemented diets that raise plasma myo-inositol levels approximately fivefold. The failure of the 2% myo-inositol diet to normalize GFR and blood flow and albumin permeation in several tissues despite markedly elevated plasma myo-inositol levels and normal or elevated tissue myo-inositol levels indicates that if vascular functional changes in these tissues are linked to altered myo-inositol levels, they are resistant to normalization by elevation of plasma myo-inositol levels. These results suggest that other factors independent of changes in relative or absolute tissue myo-inositol levels may play an important role in the pathogenesis of diabetes-induced vascular functional changes in these tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Aldose Reductase Inhibition and Glomerular Abnormalities in Diabetic Rats

We examined the effects of aldose reductase inhibition (ARI) on glomerular filtration rate (GFR), albuminuria, and kidney histology in partially insulin-treated streptozocin-induced diabetic (STZ-D) rats. After 1 mo of diabetes, GFR was elevated over control values in the STZ-D rats but was not affected by treatment with statil (an aldose reductase inhibitor). In another set of rats maintained for 7 mo, albuminuria was significantly increased in the diabetic rats from 2 mo on but was also not affected by statil treatment. Similarly, histological glomerular damage and diabetes-induced kidney hypertrophy were also greater in diabetic animals but were not altered by statil treatment. The frequency of diabetic cataracts was reduced by statil, and erythrocyte and kidney sorbitol levels were normalized, confirming the efficacy of ARI. Thus, inhibition of the aldose reductase pathway with statil does not ameliorate the hemodynamic, proteinuric, histological, or growth abnormalities in this model of diabetic nephropathy.

Autonomic neuropathy in BB rats and alterations in bladder function.

In vivo urinary bladder function was examined in BB rats after 4 and 6 mo of diabetes, and the data were correlated with morphometric changes in the pelvic and hypogastric nerves, which constitute the micturition reflex arc. After controlled bladder distension, diabetic animals revealed irregular bladder contractions at frequencies that were reduced to 33% of normal values and with significantly increased amplitudes. The abnormal micturition in diabetic animals was elicited at moderately elevated threshold volumes. These functional abnormalities of the diabetic bladder were associated with a progressive axonopathy of afferent myelinated sensory fibers and later-occurring axonal atrophy of unmyelinated efferent preganglionic fibers. These data suggest that diabetic urinary bladder dysfunction is initiated by a visceral sensory neuropathy involving the afferent limb of the micturition reflex arc.

Alteration of electrophysiological function of isolated retina from alloxan-induced diabetic rats: Effect of treatment withGinkgo biloba extract

In the first stage the authors highlight the functional impairments owing to diabetic retinopathy by performing experiments on isolated retinas of alloxan-induced diabetic rats. After 1 mo evolution of diabetes, the electroretinograms (ERG) obtained on isolated retinas had an amplitude on average 20% lower than the controls, whereas after 2 mo of diabetes, this decrease in amplitude is around 60%. In the second stage, the authors compare the electroretinograms obtained on the isolated retina of 2 mo diabetic animals, nontreated or treated per os withGinkgo biloba extract (100 mg/kg/d): These ERG have a significantly greater amplitude (p<0.001) in treated animals. The results are discussed in relation to the role of oxygenated free radicals in diabetic retinopathy, the production of these induced by platelet-activating factor (PAF), and the PAF antagonistic properties ofGinkgo biloba extract, which could participate in the preventive treatment of the visual functional impairments involved in diabetes.

Abnormal cardiac biochemistry in spontaneously diabetic Bio-Breeding/Worcester rat.

Diabetes produced by injection of alloxan or streptozotocin results in cardiac dysfunction in rats that is associated with lower cardiac contractile protein ATPase activity. The purpose of this investigation was to examine cardiac myosin biochemistry in the Bio-Breeding Worcester (BB/W) rat, a strain in which diabetes occurs spontaneously and closely resembles insulin-dependent diabetes in humans. Hearts from diabetic BB/W rats were studied at 1, 4, and 7 mo after the onset of diabetes and were compared with age-matched BB/W rats that were bred for resistance to diabetes. Calcium-stimulated myosin ATPase activity was significantly decreased after 4 and 7 mo of diabetes, and actin-activated myosin ATPase was significantly depressed at all time points. Differences between hearts from control and diabetic animals increased with the duration of diabetes. Closely associated with reductions in myosin ATPase activity in the diabetes was a shift in the isomyosin content from the normally predominant V1 to the V3 isoenzyme. Thus diabetes that results from genetic causes leads to depressed myosin enzymatic activity in the rat. Furthermore, since previous studies have shown that BB/W diabetic rats do not develop hypothyroidism, the present results support the view that altered thyroid function does not mediate the abnormalities in cardiac contractile proteins in diabetes.

Nerve Na+-K+-ATPase, conduction, and myo-inositol in the insulin-deficient BB rat.

Nerve conduction slowing in acute diabetes in animals has been associated with both a diminished axolemmal transmembrane Na+ potential and a myo-inositol-related defect in nerve Na+-K+-ATPase activity. The interaction between these two potentially related defects, their reversibility, and their possible role in the nerve conduction slowing and axonopathy of diabetes are not well defined. Therefore, the effects of rigorous insulin replacement on peripheral nerve conduction velocity, myoinositol content, and Na+-K+-ATPase activity were studied in the spontaneously diabetic BB-Wistar rat, an animal model that manifests both conduction slowing and a characteristic progressive axonopathy. Twelve weeks of sustained hyperglycemia reduced both motor conduction velocity and Na+-K+-ATPase activity in sciatic nerve. Six weeks of subsequent vigorous insulin replacement normalized the enzymatic defect but only partially corrected diminished nerve conduction velocity. Hence, nerve conduction slowing in diabetic animals may be partly attributable to reduced nerve Na+-K+-ATPase activity, but a less readily reversible component of conduction slowing probably reflects structural alterations that occur in nerve within the first 3 mo of diabetes.

Low plasma somatomedin-C in streptozotocin-induced diabetes mellitus. Correlation with changes in somatogenic and lactogenic liver binding sites.

To determine the mechanism for the decrease of somatomedin levels in insulin-dependent diabetes, the relationships among plasma immunoreactive somatomedin-C (Sm-C), plasma growth hormone (GH) and prolactin (PRL), and the somatogenic and lactogenic binding sites in liver were assessed in rats with nonketotic diabetes mellitus of different duration (1 wk or 1 mo) and severity (50 or 60 mg streptozotocin/kg BW). One week after administration of 60 mg streptozotocin (STZ)/kg, plasma Sm-C concentrations were significantly decreased (0.23 +/- 0.03 versus 0.43 +/- 0.03 U/ml in controls; mean +/- SEM, P less than 0.01). In contrast, plasma GH concentrations, bovine GH (bGH) binding, and human GH (hGH) binding were not significantly changed. After 1 mo of diabetes, no further decrease in plasma Sm-C content was observed despite a reduction in plasma GH and PRL concentrations and reduced hepatic bGH binding capacity (5 +/- 2 versus 38 +/- 4 fmol/mg protein; P less than 0.01). In the group of rats injected with 50 mg STZ/kg, the Sm-C was reduced at 1 mo but hepatic GH binding was not. In a second study, diabetic rats (75 mg STZ/kg) were treated after 3 wk with insulin (10 U lente per day for 7 days). This treatment normalized Sm-C levels and partially restored the GH binding capacity (treated: 49 +/- 4 fmol/mg protein versus untreated diabetics: 28 +/- 6 fmol/mg protein; P less than 0.01 and versus controls: 68 +/- 4 fmol/mg protein; P less than 0.05).2+ suggest that in an early phase of nonketotic diabetes, the low plasma Sm-C is not due primarily to reduced GH receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)