Calcitonin antibodies in experimental diabetes mellitus

Antibodies to calcitonin appear in blood of rats with experimental alloxan diabetes. This phenomenon is observed only under high blood sugar. At the stage of latent diabetes, i.e. during alloxan administration to the body and low blood sugar no antibodies to calcitonin are detected. It is possible that appearance of autoantibodies to calcitonin is one of pathogenetic factors of hyperglycemia development in rats with alloxan diabetes.     

Placental structure in gestational diabetes mellitus

The placenta is a transitory organ, located between the mother and the foetus, which supports intrauterine life. This organ has nutritional, endocrine and immunologic functions to support foetal development. Several factors are related to the correct functioning of the placenta including foetal and maternal blood flow, appropriate nutrients, expression and function of receptors and transporters, and the morphology of the placenta itself. Placental morphology is crucial for understanding the pathophysiology of the organ as represents the physical structure where nutrient exchange occurs. In pathologies of pregnancy such as diabetes mellitus in humans and animal models, several changes in the placental morphology occur, related mainly with placental size, hypervascularization, higher branching capillaries of the villi and increased glycogen deposits among others. Gestational diabetes mellitus is associated with modifications in the structure of the human placenta including changes in the surface area and volume, as well as histological changes including an increased volume of intervillous space and terminal villi, syncytiotrophoblast number, fibrinoid areas, and glycogen deposits. These modifications may result in functional changes in this organ thus limiting the wellbeing of the developing foetus. This review gives an overview of recurrent morphological changes at macroscopic and histological levels seen in the placenta from gestational diabetes in humans and animal models. This article is part of a Special Issue entitled: Membrane Transporters and Receptors in Pregnancy Metabolic Complications edited by Luis Sobrevia.     

Modulation of neuropathic pain in experimental diabetes mellitus

The main objective of the current article is to investigate the diabetic polyneuropathy which represents a major preoccupation within the context of high incidence of diabetes mellitus (DM) and its complications. Moreover, neuropathy may develop despite intensive hyperglycaemic control. The effect of Zn and black grape seed polyphenols (BGSP) in streptozotocin diabetic rats was studied. Zn and BGSP were administered by gavage, daily, for 16 weeks to Wistar rats that have been rendered diabetic by a single i.v. injection of streptozotocin (55 mg/kg body weight). Dysalgesia was investigated under the conditions of nociceptive stimulation through the following tests: the thermoalgesic mechanism through the tail-flick test, the hot plate test and the plantar test, and the mechanoalgesic mechanism through the algesimetric test. Thermal hyperalgesia detected in the diabetic group is significantly reduced (p?<?0.001) through the administration of polyphenols, or even better, of Zn. Diabetes-associated mechanical hyperalgesia decreased significantly (p?<?0.001) probably through the inhibition of the NMDA receptors. Administration of Zn or BGSP to the diabetic group improves glycosylated haemoglobin (HbA1c) values but does not bring them to normal. The present data suggest a favourable effect of Zn and BGSP in inhibiting diabetic complications by several mechanisms.     

Impaired cerebral vasoreactivity in type 2 diabetes mellitus

The aim of our study was to assess cerebral vasoreactivity (CVR) in type 2 diabetes mellitus (DM2) and factors which may influence on it. According to previous studies, evaluating CVR in DM2 on the similar way, the results were dubious. For the evaluation CVR we used breath holding index (BHI) and transcranial Doppler ultrasound (TCD) in 50 patients with DM2 and 50 sex- and age-matched healthy controls. We observed epidemiologic and clinic data, other vascular risk factors and laboratory parameters. We found statistically significant difference in BHI between patients with DM2 (BHI = 0.69 +/- 0.31) and age- and sex-matched healthy controls (BHI = 1.33+/-0.28) (p < 0.05 ). Because of a significant correlation between BHI and age (p < 0.001) in healthy controls we made an adjustment of BHI for age before further analyses (BHIadj). In DM2 group we found a significant correlation between BHIadj and age (p = 0.0004), fasting glycemia (p = 0.04), and albuminuria (p = 0.04) (creatinine clearance in multivariate analysis (p = 0.007)). Our study has shown that CVR is impaired in DM2 patients and that it's severity was associated with age, fasting glycemia and renal function. Functional TCD is a very good screening method for detection and monitoring of cerebral microangiopathic changes in DM2 patients.     

Impaired erythrocyte deformability precedes vascular changes in experimental diabetes mellitus.

The effect of diabetes on the red blood cell (RBC) deformability and its association with histological vascular changes was investigated in 35 streptozotocin-induced diabetic Wistar rats in a 30-day experiment and compared to 10 controls. RBC deformability was significantly impaired in the diabetic rats on day 5 (p < 0.001) and continued to deteriorate until day 20. On the 20 (th) day, the diabetic rats were randomly divided into two groups (group A: insulin-treated; group B: non-insulin-treated). A slight, non-significant (p = 0.20) improvement in RBC deformability was noticed in the insulin-treated group. In vitro incubation of RBCs with insulin did not improve the acquired RBC rigidity in either diabetic group. In contrast, it caused a significant reduction in RBC-deformability in the controls. On day 30, histological examination of arterial specimens from various sites revealed moderate to significant thickening in medium- and small-size artery and arteriole walls in both diabetic groups, with no evidence of diabetes-related changes in large, elastic-type arteries. No vascular changes were noticed in nine diabetic rats that succumbed between days 10 and 15. The results of this study indicate that reduced RBC deformability is an early manifestation of abnormal blood rheology in experimental diabetes, and precedes the evolution of vascular changes.     

Cellular mechanisms involved in experimental insulin-dependent diabetes mellitus

Many tissue-specific autoimmune diseases are mediated by the induction of autoantigen-specific T cells. These cells are believed to cause tissue damage through the production of cytokines, through direct lysis of cells expressing self-antigens, or through the induction of inflammatory responses. The escape from self-tolerance or anergy is a prerequisite for initiation of an autoimmune process. INS-HA (insulin-hemagglutinin) transgenic mice express the HA of A PR8 34 influenza virus in the pancreatic beta-cells under the rat insulin promotor. TCR-HA (T cell receptor-hemagglutinin) transgenic mice express the TCR specific for the immunodominant epitope HA110-120 from the same virus. Double transgenic (dTg) mice expressing both genes represent an excellent model for understanding the mechanism leading to autoimmune diabetes independently of susceptibility genes. In order to gain information on the breaking down of neonatal self-tolerance we studied the occurrence of insulin dependent diabetes mellitus (IDDM) after birth. Our results showed that newborn mice develop fulminant IDDM characterized by occurrence of insulitis as early as 3 days after birth, followed by hyperglycemia by 7 days, and significant hypoinsulinemia by 28 days. Such "double transgenic" mice expressing wild-type or targeted IL-4R alpha genes were examined for the onset of IDDM. Eight of eleven mice homozygous for the wild-type IL-4R alpha were hyperglycemic by 8 weeks of age, whereas only 1 of 16 mice homozygous for the targeted allele were hyperglycemic at this time. Most IL-4R alpha -/- mice remained normoglycemic to 36 weeks of age. Although only 10% of double transgenic mice homozygous for wild-type IL-4R alpha allele survived to 30 weeks, 80% of mice homozygous for the targeted allele did so. Even as late as 270 days of age, mice homozygous for the targeted allele had no insulitis or only peri-insulitis. Heterozygous mice displayed an intermediate frequency of diabetes. The IL-4R alpha chain acts as the high affinity binding chain and the principal signaling chain for IL-4; it also acts as the signaling chain for IL-13, but in this case the IL-13R alpha 1 chain conveys the bulk of the cytokine specificity. Thus, IL-4R alpha knock-out mice are unresponsive to both IL-4 and IL-13. The finding that the lack of IL-4R alpha chain protects TCR-HA, INS-HA double transgenic mice against diabetes, and death implies that either IL-4 or IL-13 plays a role in the progression of this disease. These studies demonstrate that TCR-HA, INS-HA double transgenic mice may provide a useful model to evaluate new strategies for the prevention of diabetes.     

Alpha-adrenoceptor-mediated coronary vasoconstriction is augmented during exercise in experimental diabetes mellitus.

This study tested whether alpha-adrenoceptor-mediated coronary vasoconstriction is augmented during exercise in diabetes mellitus. Experiments were conducted in dogs instrumented with catheters in the aorta and coronary sinus and with a flow transducer around the circumflex coronary artery. Diabetes was induced with alloxan monohydrate (n = 8, 40 mg/kg i.v.). Arterial plasma glucose concentration increased from 4.7 +/- 0.2 mM in nondiabetic, control dogs (n = 8) to 21.4 +/- 1.9 mM 1 wk after alloxan injection. Coronary blood flow, myocardial oxygen consumption (MVo(2)), aortic pressure, and heart rate were measured at rest and during graded treadmill exercise before and after infusion of the alpha-adrenoceptor antagonist phentolamine (1 mg/kg iv). In untreated diabetic dogs, exercise increased MVo(2) 2.7-fold, coronary blood flow 2.2-fold, and heart rate 2.3-fold. Coronary venous Po(2) fell as MVo(2) increased during exercise. After alpha-adrenoceptor blockade, exercise increased MVo(2) 3.1-fold, coronary blood flow 2.7-fold, and heart rate 2.1-fold. Relative to untreated diabetic dogs, alpha-adrenoceptor blockade significantly decreased the slope of the relationship between coronary venous Po(2) and MVo(2). The difference between the untreated and phentolamine-treated slopes was greater in the diabetic dogs than in the nondiabetic dogs. In addition, the decrease in coronary blood flow to intracoronary norepinephrine infusion was significantly augmented in anesthetized, open-chest, beta-adrenoceptor-blocked diabetic dogs compared with the nondiabetic dogs. These findings demonstrate that alpha-adrenoceptor-mediated coronary vasoconstriction is augmented in alloxan-induced diabetic dogs during physiological increases in MVo(2).     

DNA constancy and chromatin structure in some cell nuclei ofAmphiuma

Synopsis In a series of microspectrophotometric and microphotometric investigations, it has been found that in lymphocytes of the primitive amphibianAmphiuma the very large amount of Feulgen-DNA per nucleus (that is, the amount of DNA revealed by a Feulgen hydrolysis-Schiff technique) is constant within the limits of the measuring error. The Feulgen hydrolysis time had to be reduced considerably in order to bring down the extinctions (optical densities) of these very voluminous and densely staining nuclei. Off-peak absorption of cells in smears stained in the usual way with the Feulgen-Schiff method appeared to be of no value in these experiments. The relation between the Feulgen-DNA content of lymphocyte nuclei of human andAmphiuma cells, as determined from the slope of the hydrolysis curve, appeared to be around 124, which fits well with biochemical data from the literature.Cytologically, a large part of the chromatin appeared to exist in large clumps of heterochromatin. In marginated plaques of condensed chromatin, local areas of lower density occur and are in close association with nuclear pores. The dense lamina is often very pronounced in these nuclei.     

Isolation of nuclei for chromatin analysis in fission yeast.

The methods available for analysis of the chromatin of Schizosaccharomyces pombe are time consuming (>8 h) and/or result in some degradation of the chromatin. Here we report an optimised method for the preparation of spheroplasts and the isolation of nuclei which takes <25 min and is suitable for analysis of chromatin structure by micrococcal nuclease, restriction endonuclease or by immunoprecipitation.     

Glomerular hemodynamic and structural alterations in experimental diabetes mellitus

Elevated glomerular filtration rate (GFR) is a frequent finding in patients with early insulin-dependent diabetes mellitus (IDDM). The mechanisms responsible for this glomerular hyperfiltration in IDDM are unclear. Rats made diabetic with alloxan or streptozotocin, and treated daily with supplemental insulin, have moderate hyperglycemia and elevated GFR, and thus have been used to study mechanisms of glomerular hyperfiltration in diabetes. Renal micropuncture techniques have shown that single-nephron GFR (SNGFR) is elevated in moderately hyperglycemic diabetic rats. In some cases, this is because of elevated glomerular capillary pressure (Pgc), but in other cases, Pgc is normal despite elevated SNGFR. Several potential mediators of increased SNGFR have been examined, including hyperglycemia, increased glomerular prostaglandin production, and decreased sensitivity of the tubuloglomerular feedback mechanism. Renal failure is a common complication of human IDDM. Diabetic rats with long-term moderate hyperglycemia have been used to study the mechanism by which glomerular injury develops in diabetes mellitus. It has been postulated that glomerular hyperfiltration or some determinant of elevated GFR in early diabetes may ultimately cause glomerular damage, leading to a progressive loss of renal function (diabetic nephropathy). Diabetic rats with long-term moderate hyperglycemia, however, do not develop characteristic glomerular lesions of human diabetic nephropathy and, in fact, develop only minimal glomerular injury even after 1 year of diabetes. Thus, although the diabetic rat with moderate hyperglycemia may be useful to study the mechanisms of glomerular hyperfiltration in early diabetes, it may not be an appropriate model of renal failure in IDDM.     

Altered chromatin structure associated with a partial trisomy of chromosome 7 in the mouse

The chromatin of a mouse that is trisomic for part of chromosome 7 was investigated. Chromatin from trisomic tissue has a smaller average nucleosome DNA repeat length than chromatin from tissue taken from normal diploid littermates. DNA of the nucleosome cores is the same size in both normal and trisomic tissues. Not all of the nucleosome monomers have different repeat lengths. Normal and trisomic mouse kidney cells in tissue culture maintained their nucleosome repeat-length differences.     

Insulin sensitising action of chromium picolinate in various experimental models of diabetes mellitus.

Although chromium is an essential element for carbohydrate and lipid metabolism, its effects in diabetic patients are still debated. We have studied the effect of 6 week treatment with chromium picolinate (8 microg/ml in drinking water) in streptozotocin (STZ)-induced type 1 and type 2 diabetic rat models. The mechanism of anti-diabetic action of chromium picolinate was studied using C2C12 myoblasts and 3T3-L1 adipocytes. Chromium picolinate significantly decreased the area under the curve over 120 min for glucose of both STZ-induced type 1 (40mg/kg, i.v. in adult rats) and type 2 (90 mg/kg, i.p. in 2 day old rat neonates) diabetic rats without any significant change in area under the curve over 120 min for insulin as compared to controls. The composite insulin sensitivity index and insulin sensitivity index (KITT) values of both type 1 and type 2 diabetic rats were increased significantly by chromium picolinate. Treatment with chromium picolinate produced a significant decrease in elevated cholesterol and triglyceride levels in both types of diabetic rats. In 3T3-L1 adipocytes, chromium picolinate (0-10 micromol) per se did not produce any effect, however, when co-incubated with insulin it significantly increased the intracellular triglyceride synthesis (EC50 = 363.7nmol/1). Similarly in C2C12 myoblasts, chromium picolinate alone did not produce any effect, however, it significantly increased insulin-induced transport of 14C-glucose. In conclusion, chromium picolinate significantly improves deranged carbohydrate and lipid metabolism of experimental chemically induced diabetes in rats. The mechanism of in vivo anti-diabetic action appears to be peripheral (skeletal muscle and adipose tissue) insulin enhancing action of chromium.     

Urinary excretion of glycosaminoglycans and albumin in experimental diabetes mellitus

Diabetes mellitus was induced in one group of rats by a single injection of streptozotocin. The glycemia, the body weight, and the blood systolic pressure were measured every week, and the 24 h urine volume and urinary excretions of creatinine, albumin and glycosaminoglycans were measured every 2 weeks. At the end of the experiment (12 weeks) the weight and the glycosaminoglycan composition of the kidneys were determined. All the diabetic animals were hyperglycemic, hypertense, and did not gain weight during all the experimental period. Albuminuria appeared from the second week on. Rat urine was shown to contain heparan sulfate, chondroitin sulfate, and dermatan sulfate, and the glycosaminoglycan excretion decreased in all diabetic animals. The onset of the change in glyco-samino-glycan excretion rate was a very early event, appearing in the second week after diabetes induction. The main glycosaminoglycan found in normal rat kidney was heparan sulfate and, in contrast to the urine, the total kidney glycosaminoglycans increased in diabetic kidney, due to chondroitin sulfate and dermatan sulfate accumulation. The heparan sulfate concentration (per tissue dry weight) did not change. Our results suggest that quantification of urinary glycosaminoglycans may be a useful tool for the early diagnosis of diabetic nephropathy.