Streptozocin-induced Diabetic Rats Research Articles

Zopolrestat prevention of proteinuria, albuminuria and cataractogenesis in diabetes mellitus.

The aldose reductase inhibitor, Zopolrestat, reduced proteinuria and albuminuria in streptozocin-induced diabetic rats compared with both untreated diabetic and age-matched controls. Daily administration of Zopolrestat (100 mg/kg) for 4 months decreased 24 h total protein excretion to 15.07 +/- 2.17 mg from 49.97 +/- 7.94 mg/day in untreated diabetic rats. Zopolrestat protected against excretion of any array of urinary proteins with molecular weights between 30 and 100 kD. These effects were sustained throughout the 5th and 6th months of treatment. At the end of 6 months, Zopolrestat-treated diabetic rats excreted 22.77 +/- 4.39 mg/day compared to untreated diabetic rats (67.05 +/- 14.03 mg/day), a 6-fold increase in urinary protein excretion compared to age-matched nondiabetic controls (11.65 +/- 1.71 mg/day). Zopolrestat treatment for 6 months produced therapeutic effects in the lens: transparency and myo-inositol content were maintained and lens sorbitol diminished, despite elevated lens glucose. In contrast, untreated diabetic rats had opaque lenses which exhibited a 40-fold increase in sorbitol and myo-inositol depletion. In opaque lenses, ouabain-sensitive Rb influx, an index of Na-K-ATPase activity, decreased to only 53.8% of mean values in age-matched controls; the ouabain-insensitive component increased by 63.6%. Zopolrestat treatment prevented these diabetic-induced changes and maintained ouabain-sensitive and ouabain-insensitive Rb influx. Collectively, these results suggest that Zopolrestat exerts a protective effect on the slowly developing diabetic cataract, as well as reducing albuminuria and proteinuria.

Increase of voltage-sensitive calcium channels and calcium accumulation in skeletal muscles of streptozocin-induced diabetic rats

The number of voltage-sensitive calcium channels (VOCC) in triceps surae muscle membrane fractions isolated from control and streptozocin (STZ)-induced diabetic rats was determined using [ 3H]PN200-110, a dihydropyridine derivative, as a ligand. Furthermore, quantitative analysis of calcium in soleus muscle fibers was performed by the calcium oxalate-pyroantimonate method and x-ray microanalysis. The maximum binding (B max) of [ 3H]PN200-110 in skeletal muscle membrane isolated from 10-week diabetic rats (1,091 ± 77 fmol/mg protein) was increased significantly by 91% as compared with the control value (572 ± 32 fmol/mg protein), without a significant change in K d . The increase in B max of [ 3H]PN200-110 was dependent on the duration of diabetes, and was not found until 6 weeks after STZ injection. Insulin treatment for 8 weeks after induction of diabetes normalized B max to the control level (583 ± 53 fmol/mg protein). Precipitates of calcium antimonate, identified by x-ray microanalysis, were observed much more frequently in specimens from 10-week diabetic rats versus controls. The increase in the incidence of precipitates was not observed in 3-week diabetic rats and was suppressed by 8 weeks' insulin treatment. These results indicate that the number of VOCC in chronically diabetic rats was increased in the sarcolemmal membrane of skeletal muscle and that calcium was accumulated inside skeletal muscle fibers.

Vitamin E prevents diabetes-induced abnormal retinal blood flow via the diacylglycerol-protein kinase C pathway.

We have characterized effects of d-alpha-tocopherol (vitamin E) on activation of protein kinase C (PKC) and diacylglycerol (DAG) levels in retinal tissues of diabetic rats and correlated its effects to diabetes-induced changes in retinal hemodynamics. Membrane PKC specific activities were increased by 71% in streptozocin-induced diabetic rats compared with controls (P < 0.05). Western blot analysis showed that membrane PKC-beta II was increased by 133 +/- 5% (P < 0.05). Injection of d-alpha-tocopherol (40 mg/kg ip) every other day prevented the increases in membrane PKC specific activity and PKC-beta II protein by immunoblots. Diabetes-induced increases in DAG levels were also normalized by d-alpha-tocopherol treatment of 2 wk duration. Physiologically, angiographic abnormalities of retinal hemodynamics based on computerized video-based fluorescein angiography and associated with increases of DAG and membranous PKC levels were also prevented by d-alpha-tocopherol treatment in diabetic rats. The effect of d-alpha-tocopherol on retinal vascular cells was also studied. Exposure of retinal endothelial cells to 22 mM glucose for 3 days increased total DAG and [3H]palmitate-labeled DAG levels by 35 +/- 8 and 50 +/- 8% (P < 0.05), respectively, compared with exposure to 5.5 mM glucose. The presence of d-alpha-tocopherol (50 micrograms/ml) prevented the increases in total DAG and [3H]palmitate-labeled DAG levels in cells exposed to 22 mM glucose. These findings suggested that treatment with d-alpha-tocopherol can prevent diabetes-induced abnormalities in rat retinal blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effect of radix ginseng on peroxidation injury in myocardium and erythrocytes of streptozocin-induced diabetic rats

The authors have investigated the effect of Radix Ginseng on peroxidation injury in myocardium and erythrocytes of streptozocin-induced diabetic rats. In the ginseng administered group (ginseng solution 0.2 g/200 g body weight once daily lasting 15∼16 days), there was a significant decrease in the level of fasting blood glucose and lipid peroxide in myocardium and erythrocytes, in comparison with those of the model group (P<0.05). The superoxide dismutase activities in myocardium and erythrocytes of the ginseng group were increased (P<0.05), compared with those of the model group and the vitamin E treated group (vitamin E 10 mg/200 g·body weight once daily, lasting 15∼16 days). The results suggest that the mechanisms of antiperoxidation injury of ginseng might include the following: (1) lowering the level of fasting blood glucose, decreasing monosaccharide auto-oxidation and partially protecting the production of free radicals; (2) elevating the activity of enzymatic free radical scavenger in cells, such as superoxide dismutase; and (3) directly eliminating the superfluous free radicals.

Effect of insulin-like growth factor type 1 on critical-size defects in diabetic rats.

A number of investigators have reported on the clinically significant relationship between diabetes mellitus and impaired wound healing. Diabetic patients have an increased frequency of infection, delayed scar formation, and poor bony union. Investigations completed in our laboratory have demonstrated that insulin-like growth factor type 1 (IGF-1), a somatomedin C, has shown promise for accelerating bony repair. The purpose of this study was to examine the effects of recombinant IGF-1 on standardized, critical-size calvarial defects in 25 adult, male streptozocin-induced diabetic rats. From our study, it appears that IGF-1 exerts a potentiating effect on the repair of bony defects in diabetes-induced rats.

The reduction of circulating growth hormone and prolactin in streptozocin-induced diabetic male rats is possibly caused by hypothalamic rather than pituitary changes.

To gain further information on diabetes-related disorders in the somatotrophic and lactotrophic axes, we undertook a functional, morphometrical and densitometrical study of the arcuate nucleus (AN), median eminence (ME) and anterior pituitary gland of adult male rats one month after streptozocin-induced diabetes (STZ-D). The basal secretory activity of somatotrophs and lactotrophs was tested by the reverse haemolytic plaque assay (RHPA) and plasma GH and prolactin (PRL) levels were determined by RIA. The number of GH-releasing factor (GRF)-labelled axons and the amount of axonal tyrosine hydroxylase (TH)-immunoreactivity increased in STZ-D. There were no significant differences in any of the other densitometrical measurements performed on GRF-, somatostatin-, thyrotropin-releasing hormone- and TH-labelled ME axon cross-sections as well as those on tuberoinfundibular-dopaminergic neurones of the AN in STZ-D compared with control rats. Plasma GH and PRL levels and measurements on anterior pituitary GH- and PRL-labelled structures were decreased in STZ-D. However, the GH and PRL plaque areas were increased after RHPA implying that the secretory capacity of somatotrophs and lactotrophs was not impaired. Taken together, these results suggest that the accumulated GRF in the ME is due to reduced GRF release. This could account for the reduced amplitude and/or frequency of GH secretory pulses. The increased axonal TH-immunoreactivity may indicate an increased dopamine synthesis. If coupled to increased release this could, in turn, be partly responsible for the reduced plasma and anterior pituitary PRL concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of acute arterial hypertension on blood-brain barrier permeability in streptozocin-induced diabetic rats

The effect of acute arterial hypertension on blood-brain barrier (BBB) permeability was studied in streptozocin-induced diabetic rats using Evans blue as a barrier tracer. Four groups of rats were studied: Group 1, normotensive normoglycemia; Group II, normotensive + diabetes Mellitus; Group III, arterial hypertension + diabetes mellitus; Group IV, arterial-hypertension + normoglycemia. During adrenaline-induced acute arterial hypertension the mean arterial blood pressure increased in both non-diabetic and diabetic animals. Changes in BBB permeability were observed in 52% of the non-diabetic rats, and in 72% of the diabetic rats after adrenaline-induced acute arterial hypertension. Mean levels of Evans blue in the whole brain were found to be 0.63 ± 0.1 mg% in non-diabetic and 0.90 ± 0.2 mg% in diabetic rats. The difference between the non-diabetic and the diabetic rats was found to be statistically significant ( P < 0.01). From these results it was suggested that the extraversion of Evans blue albumin is more pronounced in the brains of diabetic rats in comparison with non-diabetic rats after adrenaline-induced acute hypertension, which is indicative of changes in BBB permeability due to diabetes mellitus.

Inhibition of sorbitol dehydrogenase. Effects on vascular and neural dysfunction in streptozocin-induced diabetic rats.

These experiments were undertaken to assess the role of sorbitol dehydrogenase in mediating sorbitol pathway-linked neural and vascular dysfunction in rats with streptozocin-induced diabetes. 2-methyl-4-[N,N-dimethylsulfamoyl-piperazino]-pyrimidine (S-0773), a putative inhibitor of sorbitol dehydrogenase, was given in the drinking water to control and diabetic rats. After 5 weeks of diabetes, glycosylated hemoglobin levels were increased twofold and were unaffected by S-0773. Sorbitol levels in diabetic rats were increased 11- to 14-fold in ocular tissues and sciatic nerve; S-0773 increased sorbitol levels another 4-fold or more in these same tissues but had much smaller effects in other tissues. Diabetes-associated increases in fructose levels and lactate:pyruvate ratios in retina and in sciatic nerve were markedly attenuated by S-0773. S-0773 also attenuated, but did not completely normalize, impaired caudal nerve conduction and vascular dysfunction in ocular tissues, sciatic nerve, and aorta in diabetic rats. These observations, together with other evidence, suggest that sorbitol pathway-linked vascular dysfunction (in ocular tissues, peripheral nerve, and aorta) and electrophysiological dysfunction (in peripheral nerve) induced by diabetes are more closely linked to increased oxidation of sorbitol to fructose than to putative osmotic effects of elevated sorbitol levels or redox and metabolic imbalances associated with reduction of glucose to sorbitol by aldose reductase.

Inhibition of sorbitol dehydrogenase. Effects on vascular and neural dysfunction in streptozocin-induced diabetic rats

Inhibition of sorbitol dehydrogenase. Effects on vascular and neural dysfunction in streptozocin-induced diabetic rats

Reduced Levels of mRNA Encoding Endoskeletal and Growth-Associated Proteins in Sensory Ganglia in Experimental Diabetes

This study investigated changes in levels of mRNAs encoding the three neurofilament (NF) proteins NF-L (low), NF-M (medium), and NF-H (high) and two growth-associated proteins, GAP-43 and T alpha 1 alpha-tubulin, in lumbar dorsal root ganglia of control and streptozocin-induced diabetic rats. After 8 weeks of diabetes the animals were killed, and total RNA was isolated from the L4 and L5 dorsal root ganglia and subjected to Northern blotting, with constant amounts of total RNA loaded onto each lane. A truncated sense RNA for GAP-43 was included as an internal standard during RNA isolation to enable accurate quantification of mRNA levels. The filters were probed sequentially with 32P-labeled cDNAs encoding NF-L, NF-M, NF-H, GAP-43, T alpha 1 alpha-tubulin, and citrate synthase. Hybridizing RNAs were detected by autoradiography and quantified by image analysis. Hybridization signals were normalized to those of the internal standard. In diabetes, NF-L mRNA levels (2.5- and 4-kilobase [kb] transcripts) were decreased by 35 (P = 0.002) and 34% (P < 0.001), respectively, the NF-H mRNA level was decreased by 65% (P < 0.001), but the NF-M mRNA remained unchanged. T alpha 1 alpha-tubulin and GAP-43 mRNA levels were reduced by 56 (P < 0.001) and 30% (P < 0.05), respectively. Levels of citrate synthase mRNA were unchanged. These data indicate a selective defect of expression of growth-associated and endoskeletal proteins in experimentally induced diabetes.

Increased calcium-channel currents of pancreatic β cells in neonatally streptozocin-induced diabetic rats

Using a whole-cell patch-clamp technique, voltage-dependent Ca 2+-channel activities were found to be increased in cultured single β cells isolated from neonatally streptozocin-induced diabetic rats (NSZ rats). The current-voltage relationship and inactivation time course of Ba 2+ currents via L-type Ca 2+ channels were indistinguishable between NSZ and control rats. However, the current density observed in NSZ rats was significantly greater than that in control rats. Ba 2+ currents via T-type Ca 2+ channels were also found to be enhanced in NSZ β cells. The insulin-secretory capacity of cultured pancreatic islets in response to a depolarizing stimulus (20 mmol/L arginine or 30 mmol/L KCl) in the presence of 11.1 mmol/L glucose was augmented in NSZ rats, whereas that in response to 11.1 and 16.7 mmol/L glucose alone was significantly reduced. It is concluded that the impaired insulinotropic action of glucose in β cells in NSZ rats is not due to reduced activity of voltage-dependent Ca 2+ channels. The fact that insulin secretion induced by a depolarizing stimulus was enhanced in NSZ rats may be related to the augmented activity of the voltage-dependent calcium current found in NSZ β cells.

Diabetes-Associated Mesenteric Vascular Hypertrophy Is Attenuated by Angiotensin-Converting Enzyme Inhibition

In experimental diabetes, the mesenteric vascular tree undergoes hypertrophy, and this is associated with an increase in mesenteric angiotensin-converting enzyme (ACE) levels. The aim of this study was to determine if inhibition of mesenteric ACE by ACE inhibition would influence diabetes-associated mesenteric vascular hypertrophy. Control or streptozocin-induced diabetic rats were randomized to receive no drug or the ACE inhibitor perindopril. In addition, other diabetic rats were randomized to receive either low-dose insulin that does not alter glycemic control or high-dose insulin, administered as a silastic pellet to achieve euglycemia. After 3 weeks, animals were killed for measurement of mesenteric ACE, vessel weight, and wall:lumen ratio. Diabetes was associated with increased mesenteric ACE levels, increased vessel weight, and an increase in the wall:lumen ratio. ACE inhibition, despite no effect on glycemic control, food intake, urinary urea excretion, or gut weight, prevented the increase in mesenteric ACE levels and attenuated mesenteric vascular hypertrophy as assessed by weight or wall:lumen ratio. The increase in staining by an antibody to the endothelial product, von Willebrand factor, in diabetic rats was totally prevented by perindopril treatment. Euglycemia but not low-dose insulin therapy in the diabetic rats normalized mesenteric vessel ACE, weight, and wall:lumen ratio. In conclusion, ACE inhibition may have a specific role in preventing diabetes-associated vascular hypertrophy, an important process in the genesis of micro- and macrovascular diabetic complications.

Reinnervation of allografted pancreatic islets in the rat liver.

Rat pancreatic islets were allografted in the liver and were studied morphologically in order to evaluate possible reinnervation. Islets isolated from rat pancreas were allotransplanted in the liver of streptozocin-induced diabetic rats via the portal vein. Electron microscopy revealed nerve endings with synaptic vesicles in the transplanted islets 100 days after transplantation, whereas axons in the islets appeared to degenerate several hours after isolation and prior to transplantation. These findings suggest that the nerve endings observed in the transplanted islets regenerate from nerves that innervate the recipient's liver. The tissue specimens were also investigated immunohistochemically using antityrosine hydroxylase antibody, and histochemically by the modified Karnovsky and Roots' method for visualizing acetylcholinesterase. Some nerve endings in the transplanted islets reacted positively to antityrosine hydroxylase antibody. Acetylcholinesterase was visualized in other nerves. These results indicate that norepinephrine- and acetylcholinesterase-containing nerves may reinnervate the transplanted islets.

Tissue-specific regulation of the growth hormone receptor gene in streptozocin-induced diabetes in the rat

Abnormalities of GH secretion and clearance are well-documented in poorly controlled insulin-dependent diabetes mellitus (IDDM), but the contribution of the receptor (GHR) and the GH-binding protein (GHBP) to these abnormalities has not been defined. We studied the expression of the GHR/GHBP gene in the livers, hearts and kidneys in streptozocin-induced diabetes (STZ-D) in the rat. GHR and GHBP mRNA levels were measured by Northern blot and ribonuclease protection assays. Whereas levels of GHR and GHBP mRNA were significantly decreased in liver and heart of STZ-D rats when compared with the control group (P < 0.01), GHR mRNA was significantly increased in the kidneys of STZ-D rats (P = 0.03). Six days of insulin treatment did not significantly alter the levels of GHR/GHBP mRNA in the liver or heart of STZ-D rats, but significantly decreased GHBP mRNA (P = 0.04) in the kidney. Circulating IGF-I was reduced, as was IGF-I mRNA in the liver and heart of STZ-D rats; only circulating IGF-I was restored by insulin treatment. Neither STZ-D nor insulin treatment affected IGF-I or IGF-I receptor mRNA concentrations in the kidney. We conclude that (1) STZ-D modulates the expression of the GHR/GHBP gene and (2) that these changes in GHR/GHBP mRNA concentrations are tissue-specific; STZ-D decreases GHR/GHBP mRNA in liver and heart tissue but increases GHR mRNA concentrations in the kidney. Our results indicate a role for decreased numbers of hepatic GHRs in the pathogenesis of resistance to GH's actions in terms of IGF-I generation and promotion of linear growth in IDDM. We postulate that increased GHR expression in the kidney may be involved in the renal complications of IDDM.

Calcein Fluorophotometry in Streptozocin-Induced Diabetic Rats

Calcein was used in vitreous fluorophotometry (VF) to study the blood-retinal barrier (BRB) in rats with streptozocin-induced diabetes. Calcein was injected intravenously in 18 diabetic rats and sodium fluorescein (NaF) in 12 diabetic rats. VF was performed at 1, 2, 4, 6, 9, and 21 hours following the single injection in these diabetic rats; it was also performed at these times in 24 normal (control) rats. On another day, the same experiment was performed using NaF. There was no significant difference between the two dyes in the diabetic and nondiabetic rats at 1 hour. However, at 4 hours and at later measurement points, there was dye leakage into the vitreous, peaking at 9 hours; the leakage was significantly greater in the diabetic rats. Also, the leakage was significantly greater with calcein than it was with NaF. The data demonstrate that calcein circulates longer and at higher levels than NaF and thus is probably more useful for BRB integrity studies.

Persistence of disturbed adipocyte metabolism in sterptozocin-induced diabetic rats despite near-euglycemia with phlorizin

It is widely accepted that hyperglycemia per se incites and perpetuates the diabetic state be adverse effects on β cell insulin secretion and peripheral insulin action. Examination of the latter locus has revealed glucose-related abnormalities in facilitated glucose transport. Beyond the plasma membrane, however, there is scant data examining whether hyperglycemia influences important intracellular metabolic events. We recently described a sizable reduction in post-transport, in situ metabolism in permeabilized fat cells from streptozocin-induced diabetic rats. Of importance, the diabetes-related deficit was entirely ameliorated by insulin therapy. In this study we examined whether hyperglycemia per se contributes to this altered intracellular metabolic effect. By infusing phlorizin, near euglycemia was achieved for at least four days in streptozocin-induced diabetic rats. The phlorizin-treated diabetic rats had improved (intact cell) rates of insulin-stimulated 2-deoxyglucose uptake. Despite this, permeabilized fat cell studies revealed non improvement or deterioration in diabetic intracellular metabolism as measured by both the oxidation of [6- 14C]glucose-6-phosphate via the citric acid cycle or its incorporation into triglyceride. We conclude that hypoinsulinemia, and not hyperglycemia, mediates the disturbance in porous diabetic adipocyte cellular metabolism.

Effect of propionate on in vivo carbohydrate metabolism in streptozocin-induced diabetic rats

Undigested carbohydrates and some dietary fibers are fermented in the large intestine to form short-chain fatty acids (SCFA), including acetate, propionate, and butyrate. It has been suggested that some of the beneficial effects of high-carbohydrate, high-fiber diets on carbohydrate and lipid metabolism are mediated by the metabolism of SCFA in the liver. Propionate has been shown in vitro to decrease glucose production in rat hepatocytes. The aim of the present study was to investigate the effects of propionate on carbohydrate metabolism in normal and streptozocin (STZ)-induced diabetic male Sprague-Dawley rats. Rats were fed a high-fat diet with or without sodium propionate supplementation (either 0.5% or 5% wt/wt) for 4 weeks. At the completion of the feeding period, body weight and liver glycogen concentrations were significantly decreased in STZ-diabetic rats and were unaffected by propionate supplementation. Although STZ-diabetic animals had elevated fasting plasma glucose, cholesterol, and triglyceride levels relative to nondiabetic rats, propionate supplementation had no significant effect on these parameters in either group. Basal and insulin-stimulated carbohydrate metabolism were assessed using the euglycemic clamp technique in overnight-fasted animals with 3(H)-6-glucose infusion. As expected, basal hepatic glucose production (HGP) was higher and the metabolic clearance rate of glucose (MCR) was lower in STZ-diabetic rats. High-dose insulin infusion (3 mU · kg −1 · min −1) suppressed HGP in nondiabetic and diabetic animals and increased the MCR in nondiabetic animals. However, propionate supplementation did not alter basal or insulin-stimulated HGP or the MCR in either nondiabetic or diabetic animals. It is concluded that oral propionate supplementation had no detectable effect on carbohydrate or lipid metabolism in either nondiabetic or STZ-diabetic rats.

Study of the sensitivity of the diabetes-induced pain model in rats to a range of analgesics

The streptozocin-induced diabetic rat has been put forward as a model of chronic pain with signs of hyperalgesia and allodynia that may reflect signs observed in diabetic humans. The aim of this work was to assess, in streptozocin-induced diabetic rats, the pharmacological activity to several analgesic drugs known to be effective (clomipramine, amitriptyline, desipramine, clonidine, lidocaine), ineffective (aspirin), or with a doubtful effectiveness (morphine) in human painful diabetic neuropathy. The animals were submitted to a mechanical pain test (paw pressure) and the ability of the drugs to reverse diabetes-induced hyperalgesia was tested. The tested antidepressants (0.125–8 mg/kg, i.v.) were slightly effective in diabetic rats; amitriptyline and clomipramine induced a weak effect, whereas desipramine was more active, suggesting noradrenergic specificity. This was confirmed by the effectiveness of clonidine (50, 100, 150 μg/kg, s.c.). Lidocaine (1–9 mg/kg, i.v.) had prolonged efficacy on mechanical hyperalgesia. Aspirin (100 mg/kg, i.v.) was without effect and morphine (0.5–4 mg/kg, i.v.) induced a dose-dependent antinociceptive effect but at doses twice as high as those used in normal rats. These results demonstrate the high pharmacological predictivity of this model of painful diabetes and suggest that in this pathological condition, among the drugs acting on monoaminergic transmission, noradrenergic drugs seem the most active.

Metabolic effect of PGE 1 analogue 01206.αCD on nerve Na +-K +-ATPase activity of rats with streptozocin-induced diabetes is mediated via cAMP: Possible role of cAMP in diabetic neuropathy

We investigated the dose-dependent effects of prostaglandin E 1 (PGE 1) analogue, OP1206.αCD (OP), on motor nerve conduction velocity (MNCV), nerve blood flow (NBF) and Na +-K +-ATPase (ATPase) activity in streptozocin-induced diabetic rats. At 10 μg/kg/day, OP ameliorated MNCV and NBF, but no ATPase activity, whereas at 30 μg/kg/day it increased MNCV and ATPase activity, but not NBF. These results suggested a possible direct metabolic effect of OP, at least at a certain dose, on ATPase activity independent of NBF. Since PGE 1 exerts an effect on nerve cAMP content, we conducted an in vitro study to clarify the relationship of cAMP to the modulation of ATPase activity in diabetic nerves. We studied sciatic nerves isolated from 53 rats with streptozocin-induced diabetes that had exhibited hyperglycemia for 6 wk. OP increased the activity of ATPase and the accumulation of cAMP in a dose-dependent manner. Dibutyryl cAMP, a cAMP analogue, and aminophylline, which increases nerve cAMP content, enhanced ATPase activity in a dose-dependent manner. In addition, the increased activity of ATPase in diabetic nerves produced by OP was suppressed by a protein kinase inhibitor, H8. These results suggest that ATPase activity in diabetic nerves might be regulated or modified by cAMP and, possibly, by protein kinase A, a finding that is important for clarifying the pathogenesis of diabetic neuropathy and for developing new approaches to treatment.

Diabetes increases hepatic hydroxymethyl glutaryl coenzyme a reductase protein and mRNA levels in the small intestine

Previous studies have shown that both cholesterol synthesis and the activity of hepatic hydroxymethyl glutaryl coenzyme A (HMG CoA) reductase, the rate-limiting enzyme in cholesterol synthesis, are increased in the small intestine of a wide variety of different animal models of diabetes. In the present study, we demonstrate that the mass of HMG CoA reductase protein is increased in the small intestine of both streptozocin-induced diabetic rats (2.5-fold) and streptozocin/alloxan-induced diabetic dogs (2.4-fold). These increases in HMG CoA reductase protein mass are of a magnitude similar to the previously observed increases in either HMG CoA reductase activity and/or cholesterol synthesis in the small intestine of diabetic animals. Furthermore, mRNA levels for HMG CoA reductase in the small intestine of diabetic rats and diabetic dogs are increased 2.1- and 1.7-fold, respectively. These results suggest that the increase in HMG CoA reductase protein levels in the small intestine of diabetic animals is due to an increase in mRNA levels. In contrast, mRNA levels for HMG CoA reductase in the liver of diabetic rats are not increased. Additionally, mRNA levels for the low-density lipoprotein (LDL) receptor are also increased in the small intestine of diabetic animals (rats, 43%; dogs, 59%). The increase in small-intestinal cholesterol synthesis has the potential for adversely affecting lipoprotein metabolism and increasing the risk of atherosclerosis in diabetes.