Effect of insulin-induced hypoglycaemia on the peripheral nervous system: focus on adaptive mechanisms, pathogenesis and histopathological changes.

Insulin-induced hypoglycaemia (IIH) is a common acute side effect in type 1 and type 2 diabetic patients, especially during intensive insulin therapy. The peripheral nervous system (PNS) depends on glucose as its primary energy source during normoglycaemia and, consequently, it may be particularly susceptible to IIH damage. Possible mechanisms for adaption of the PNS to IIH include increased glucose uptake, utilisation of alternative energy substrates and the use of Schwann cell glycogen as a local glucose reserve. However, these potential adaptive mechanisms become insufficient when the hypoglycaemic state exceeds a certain level of severity and duration, resulting in a sensory-motor neuropathy with associated skeletal muscle atrophy. Large myelinated motor fibres appear to be particularly vulnerable. Thus, although the PNS is not an obligate glucose consumer, as is the brain, it appears to be more prone to IIH than the central nervous system when hypoglycaemia is not severe (blood glucose level ≤ 2 mm), possibly reflecting a preferential protection of the brain during periods of inadequate glucose availability. With a primary focus on evidence from experimental animal studies investigating nondiabetic IIH, the present review discusses the effect of IIH on the PNS with a focus on adaptive mechanisms, pathogenesis and histological changes.

Subchronic oral toxicity study on the three flavouring substances: octan-3-ol, 2-methylcrotonic acid and oct-3-yl 2-methylcrotonate in Wistar rats.

Groups of 10 male and 10 female rats were administered 0, 25, 100 or 400 mg octan-3-ol/kg body weight per day, 77 mg 2-methylcrotonic acid/kg body weight per day or 163 mg oct-3-yl 2-methylcrotonate/kg body weight per day by gavage for 90 days. Relative liver weights of high-dose octan-3-ol males, and males and females dosed with oct-3-yl 2-methylcrotonate were significantly greater than those of the control. In male and female rats dosed with the highest level of octan-3-ol and in male rats dosed with 2-methylcrotonic acid, incidences of bile duct proliferation were increased. In the kidneys of males dosed with mid- and high level of octan-3-ol and oct-3-yl 2-methylcrotonate, tubular karyomegaly and desquamation of tubular epithelial cells were observed. Based on increased liver weight and microscopic evaluation of the liver and kidney, a no-observed-effect level (NOEL) of 25 mg/kg for octan-3-ol in rats was established. The histopathological evaluation of the liver of rats dosed with oct-3-yl 2-methylcrotonate revealed lesions corresponding to the lesions seen in rats dosed mid-dose with octan-3-ol. This observation is in accordance with the general assumption that oct-3-yl 2-methylcrotonate is completely hydrolysed to octan-3-ol and 2-methylcrotonic acid. However, when comparing the liver histopathology of oct-3-yl 2-methylcrotonate and 2-methylcrotonic acid and the kidney lesions of all three substances, conflicting results were seen and the present study does not allow the conclusion to be drawn that oct-3-yl 2-methylcrotonate and structurally-related esters are completely hydrolysed, at least under the conditions of the present study.

The influence of simple sugars and starch given during pre- or post-initiation on aberrant crypt foci in rat colon.

The aim of the present study was to investigate the enhancing effect of dietary sugar on the development of aberrant crypt foci (ACF) in male F344 rats initiated with azoxymethane (AOM). The potential role of sugar as either a co-initiator or a promoter was investigated by giving diets high in sucrose and dextrin (61%) during either the pre-initiation, the initiation, and/or the post-initiation stage of the ACF development. The colonic cell proliferation, activity of colonic phase II enzymes, and a biomarker of lipid peroxidation were additionally examined in order to obtain information on the specific mechanisms involved in the suggested effect of sucrose and dextrin on ACF development. The number of large sized and the total number of ACF were significantly increased by feeding sucrose and dextrin in the post-initiation period. No positive association between colonic cell proliferation and ACF was seen. The level of oxidative stress in the cytosol from the proximal colon and colonic glutathione transferase and quinone reductase was not affected by the sugar treatments. The overall results from this study show that sucrose and dextrin enhance the number of preneoplastic lesions in AOM-initiated rats, and act primarily as promoters in the development of ACF.

IQ (2-amino-3-methylimidazo[4,5-f]quinoline)-induced aberrant crypt foci and colorectal tumour development in rats fed two different carbohydrate diets.

In most aberrant crypt foci (ACF) and colorectal tumour studies, chemical carcinogens not normally found in food have been used as initiators. In the present study the food-related compound, IQ (2-amino-3-methylimidazo[4,5-f]quinoline), has been used. A diet high in refined carbohydrates has been associated with enhanced development of ACF and colorectal cancer in humans. The present study was designed as an integrated part of our earlier published ACF study and follows the animals until tumour development. The aim of the study was to investigate (1) the effect of a refined carbohydrate-rich diet on the development of IQ-induced ACF over time and (2) possible correlation between early and late ACF and/or colorectal tumour development. The study showed that a feeding regimen with continuous doses of 0.03% IQ in the diet for 14 weeks, followed by 32 weeks without IQ was able to induce tumours in the rat colon, liver, skin and Zymbal gland. The data demonstrate that a sucrose-rich diet enhance ACF development. A correlation between the outcome of early and late ACF was seen. However, as the tumour incidence of this study was very low it was not possible to obtain a meaningful correlation between ACF development and colorectal tumour incidence.

Transport of paraquat by isolated renal proximal tubular segments from rabbits.

Paraquat is a non-selective herbicide, which induces lung, liver and kidney damage in mammalian species. Because paraquat is mainly eliminated by the kidneys, the induced kidney damage may suppress excretion and enhance toxicity of paraquat in other organs. Since proximal tubules appear to be the target segment of the nephron, this study focuses on transport of paraquat by isolated proximal tubular segments from rabbits. Proximal tubules were isolated using a combined magnetic iron perfusion and collagenase method. Incubations were carried out at 25 degrees under 100% oxygen or nitrogen for varying times at different concentrations of paraquat. Proximal tubules accumulated paraquat by a slow process, which was non-saturable in the concentration range (0.1-5 microM) examined. Tubular excretion of cations involves transport across both basolateral and luminal membranes of the cell. The basolateral uptake of paraquat was inhibited by low temperature, low medium pH and quinine. In contrast to quinine, tetraethylammonium enhanced paraquat accumulation probably by trans-stimulating the basolateral uptake. Incubation under nitrogen enhanced paraquat accumulation possibly by reducing the transport out of the cell at the luminal membrane. Thus, this study shows that proximal tubules accumulate paraquat by an active process related to the cation transport mechanism.

Lack of histological cerebellar changes in Wistar rats given pulegone for 28 days. Comparison of immersion and perfusion tissue fixation.

Pulegone was given orally by gavage to groups of 28 SPF Wistar rats at dosage levels of 0 or 160 mg/kg body weight per day for 28 days. Clinically treated animals showed slackness, depression, decreased food consumption, and body weight. The loss of body weight was accompanied by a marked decrease in plasma creatinine. In contrast to earlier results, this study did not reveal occurrence of cyst-like spaces in the white matter of cerebellum using either perfusion or immersion tissue fixation techniques. Pulegone increased plasma alkaline phosphatase and relative liver weight indicating an adverse effect on the liver.

The cytotoxic effect of paraquat to isolated renal proximal tubular segments from rabbits.

Paraquat (PQ) induces lung, liver and kidney damage. Since PQ mainly is eliminated by the kidney, the kidney damage is of particular importance to the outcome of PQ poisoning. The exact toxic mechanism of PQ is still unclear but it is assumed to involve redox cycling and formation of reactive oxygen species. In this study, further investigations on the toxic mechanism and metabolic effects of PQ were performed using isolated renal proximal tubules from rabbits. Proximal tubules were isolated using a combined iron perfusion and collagenase method. Suspended tubules were incubated for varying periods and concentrations of PQ at 25 or 37 degrees C in Krebs-Ringer phosphate buffer or HCO3-/CO2 buffer. The cytotoxic effect of PQ was evaluated by (1) markers of oxidative stress: status of glutathione (GSH/GSSG) and formation of malondialdehyde (MDA); and (2) markers of tubular metabolism: oxygen consumption (QO2), transport of 14C-p-aminohippuric acid (PAH) and 14C-tetraethylammonium (TEA). Using 0.5 and 5 mM PQ, the GSH/GSSG ratio decreased whereas formation of MDA increased indicating oxidative stress. PQ reduced the accumulation of PAH and TEA, the basal QO2 and the ouabain sensitive QO2 indicating inhibition of the Na/K-ATPase. Nystatin-stimulated QO2 was reduced by PQ, excluding inhibition of Na+ entry as a possible cytotoxic mechanism and suggesting mitochondrial injury. This was confirmed by measuring FCCP-uncoupled QO2. Thus high concentrations of PQ appear to disrupt mitochondrial electron chain transfer resulting in reduction of metabolic functions.