Fatigue Analysis of Welded Joints Using a Thin-Walled Al/Fe Explosive Welded Transition Joints.

The study presents an analysis of S355J2+N steel and AA5083 aluminum alloy welded structural joints using explosion welded transition joints of reduced thickness. The transition joint thickness reduction significantly hinders the welding of the joints due to the risk of damage to the Al/steel interface as a result of the high temperatures during welding. In the previous article, the strength of the transition joint was analyzed but ship structures, apart from static loads, are subjected to many different cyclical loads. Welded structural joints are analyzed to determine the welding influence on the fatigue life and fracture type of the transition joints. The results of the fatigue tests show that the fatigue damage in the specimens occurs in the aluminum welded joint, and not in the explosively welded joint. The damage obtained was characteristic of cruciform welded joint specimens and both types of root and toe damage occurred. Based on the obtained results, fatigue curves for the joint were determined and compared to the fatigue curves for the AA5083 base material. The experimental fatigue curve was also compared with the design curve for welded aluminum structures from Eurocode. The conducted analysis showed the possibility of using Al/steel explosion welded transition joints of reduced thickness to transfer cyclical loads.

Verification of Selected Failure Criteria for Adhesive Bonded Elements with Different Stiffness through the Use of Methacrylic Adhesive.

This study presents the testing results of methacrylic adhesive single-lap joints made from elements with different stiffness and of the adhesive itself, using cast specimens. Methods for the preparation and testing of material specimens of the adhesive joints have been presented. Moreover, an attempt was undertaken to determine the strength criterion and find out which of the presented calculation methods enables the most precise assessment of strength in the tested group of single-lap joints, that differ in terms of the adhered stiffness and thickness. For this purpose, C45 steel and 5754 aluminium flat bars were bonded. Stress distributions were determined for failure forces obtained in the experiment by means of three basic analytic and numerical methods. Stress and strain states were compared, indicating the highest consistency for the value of normal peel stresses acting in the direction perpendicular to the direction of the joint tension. Reduced stresses provided by the analyses reached values higher than those which were achieved during the specimen tension testing.

Spexin Modulates Functions of Rat Endocrine Pancreatic Cells.

OBJECTIVES: Spexin is a peptide whose action is poorly understood but which is expressed in many tissues. This encouraged us to investigate the potential role of spexin in the regulation of pancreatic secretion. METHODS: Cells/islets were incubated with different concentrations of glucose and spexin to measure insulin secretion. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays and BrdU (5-bromo-2'-deoxyuridine) tests were performed to assess the viability and proliferation of pancreatic islets after spexin treatment. Real-time polymerase chain reaction was used to detect messenger RNA expression for insulin, insulin receptor, and Pdx (pancreatic duodenal homeobox-1). RESULTS: Insulin secretion from cultured cells and isolated islets was reduced by spexin at 16 mM glucose level. In obese rats, insulin secretion was decreased after injection with spexin. Spexin treatment showed an increase in cultured cells and pancreatic islets cell viability and proliferation as well as an increase in proliferating cell nuclear antigen protein level. In contrast, a decrease in insulin and Pdx gene expression was found. CONCLUSIONS: The effects of spexin on insulin secretion in vitro and in vivo and also on cells viability and proliferation confirm that this peptide may be strongly involved in the pathogenesis of diabetes or its recovery.

GLP1 and GIP are involved in the action of synbiotics in broiler chickens.

BACKGROUND: In order to discover new strategies to replace antibiotics in the post-antibiotic era in meat-type chicken production, two new synbiotics were tested: (Lactobacillus salivarius IBB3154 plus galactooligosaccharide (Syn1) and Lactobacillus plantarum IBB3036 plus raffinose family oligosaccharides (Syn2). METHODS: The synbiotics were administered via syringe, using a special automatic system, into the egg air chamber of Cobb 500 broiler chicks on the 12th day of egg incubation (2 mg of prebiotics + 105 cfu bacteria per egg). Hatched roosters (total 2,400) were reared on an experimental farm, kept in pens (75 animals per pen), with free access to feed and water. After 42 d animals were slaughtered. Blood serum, pancreas, duodenum and duodenum content were collected. RESULTS: Syn2 increased trypsin activity by 2.5-fold in the pancreas and 1.5-fold in the duodenal content. In the duodenum content, Syn2 resulted in ca 30% elevation in lipase activity and 70% reduction in amylase activity. Syn1 and Syn2 strongly decreased expression of mRNA for GLP-1 and GIP in the duodenum and for GLP-1 receptors in the pancreas. Simultaneously, concentrations of the incretins significantly diminished in the blood serum (P < 0.05). The decreased expression of incretins coincides with changed activity of digestive enzymes in the pancreas and in the duodenal content. The results indicate that incretins are involved in the action of Syn1 and Syn2 or that they may even be their target. No changes were observed in key hormones regulating metabolism (insulin, glucagon, corticosterone, thyroid hormones, and leptin) or in metabolic indices (glucose, NEFA, triglycerides, cholesterol). Additionally, synbiotics did not cause significant changes in the activities of alanine and aspartate aminotransferases in broiler chickens. Simultaneously, the activity of alkaline phosphatase and gamma glutamyl transferase diminished after Syn2 and Syn1, respectively. CONCLUSION: The selected synbiotics may be used as in ovo additives for broiler chickens, and Syn2 seems to improve their potential digestive proteolytic and lipolytic ability. Our results suggest that synbiotics can be directly or indirectly involved in incretin secretion and reception.

Changes in obestatin gene and GPR39 receptor expression in peripheral tissues of rat models of obesity, type 1 and type 2 diabetes.

BACKGROUND: Obestatin has a role in regulating food intake and energy expenditure, but the roles of obestatin and the GPR39 receptor in obesity and type 1 and type 2 diabetes mellitus (T1DM and T2DM, respectively) are not well understood. The aim of the present study was to investigate changes in obestatin and GPR39 in pathophysiological conditions like obesity, T1DM, and T2DM. METHODS: Using rat models of diet-induced obesity (DIO), T1DM and T2DM (n = 14 per group), obestatin, its precursor protein preproghrelin, and GPR39 expression was investigated in tissues involved in glucose and lipid homeostasis regulation. Furthermore, serum obestatin and ghrelin concentrations were determined. RESULTS: Serum obestatin concentrations were positively correlated with glucagon (r = 0.6456; P < 0.001) and visfatin (r = 0.5560; P < 0.001), and negatively correlated with insulin (r = -0.4362; P < 0.05), adiponectin (r = -0.3998; P < 0.05), and leptin (r = -0.4180; P < 0.05). There were differences in GPR39 and preproghrelin expression in the three animal models. Hepatic GPR39 and preproghrelin mRNA expression was greater in T1DM, T2DM, and obese rats than in lean controls, whereas pancreatic GPR39 mRNA and protein and preproghrelin mRNA expression was decreased in T1DM, T2DM, and DIO rats. Higher GPR39 and preproghrelin protein and mRNA levels were found in adipose tissues of T1DM compared with control. In adipose tissues of T2DM and DIO rats, GPR39 protein levels were lower than in lean or T1DM rats. Preproghrelin mRNA was higher in adipose tissues of T1DM, T2DM, and DIO than lean rats. CONCLUSION: We hypothesize that changes in obestatin, GPR39, and ghrelin may contribute to metabolic abnormalities in T1DM, T2DM, and obesity.

Resistin is produced by rat pancreatic islets and regulates insulin and glucagon in vitro secretion.

Resistin participates in the regulation of energy homeostasis, insulin resistance, and inflammation. The potential expression in pancreas, and modulation of the endocrine pancreas secretion by resistin is not well characterized, therefore, we examined it on several levels. We examined the localization of resistin in rat pancreatic islets by immunohistochemistry and immunofluorescence, and the potential presence of resistin mRNA by RT-PCR and protein by Western Blot in these structures. In addition, we studied the regulation of insulin and glucagon secretion by resistin in pancreatic INS-1E ß- and InR-G9 α-cell lines as well as isolated rat pancreatic islets. We identified resistin immunoreactivity in the periphery of rat pancreatic islets and confirmed the expression of resistin at mRNA and protein level. Obtained data indicated that resistin is co-localized with glucagon in pancreatic α-cells. In addition, we found that in vitro resistin decreased insulin secretion from INS-1E cells and pancreatic islets at normal (6 mM) and high (24 mM) glucose concentrations, and also decreased glucagon secretion from G9 cells and pancreatic islets at 1 mM, whereas a stimulation of glucagon secretion was observed at 6 mM glucose. Our results suggest that resistin can modulate the secretion of insulin and glucagon from clonal ß or α cells, and from pancreatic islets.

The influence of active exercise in low positions on the functional condition of the lumbar-sacral segment in patients with discopathy.

BACKGROUND: Pain in the lower segments of the spine is among the most frequent symptoms in industrialized countries. Injuries to intervertebral discs are the cause of this kind of discomfort in 90% of cases. The factors promoting the disease are: physical activity limitation, prolonged sitting position, overweight and bad movement stereotypes. New methods of treating sacral pain ignore the aspect of weakening the muscle force and do not introduce active exercise to the program of rehabilitation. OBJECTIVES: The aim of the work was to describe the influence of active exercise in low positions on the functional condition of patients with L-S segment discopathy. MATERIAL AND METHODS: The examination group consisted of 20 patients, including 17 women and 3 men. The examination was conducted twice, before and after a two-week long series of rehabilitation. The examined patients practiced a 20-minute exercise program for 10 days. The subjective part of the examination referred to pain discomfort felt by the patients and existing difficulties in performing everyday activities. The objective part included the measurement of movement range of the lumbar segment with the use of Schober's test, finger-to-floor test and spine rotation in the sitting position. RESULTS: It was shown that intervertebral disc disease may lead to spine flexibility limitation and to pain occurrence. CONCLUSIONS: Practicing active exercise in low positions significantly improves the movement range and body posture and it reduces pain in the lower segments of the spine. Moreover, the patient's functional abilities are improved while performing everyday activities.

Influence of short-term L-arginine supplementation on carbohydrate balance in rats with ischemia-reperfusion syndrome.

BACKGROUND: There are studies showing stimulative effect of arginine on insulin secretion. This mechanism is not fully explained. The effects of the impact of arginine on carbohydrate balance under the conditions of ischemia and reperfusion remain to be determined. The aim of this study is the evaluation of the influence of short-term L-arginine supplementation on the concentration of glucose and insulin in blood and insulin binding in rat skeletal muscle under the conditions of ischemia and reperfusion. METHODS: The study was conducted on male Wistar rats with average body mass 250 ± 30 g. Animals were divided into four groups: Group I - control, Group II - placebo, Group III - L-arginine 500 mg/kg/24 h for 5 days, Group IV - L-arginine and L-NAME (75 µmol/rat/24 h) for 5 days. Each group was divided into subgroups depending on duration of ischemia and reperfusion. Acute ischemia of hind limb was induced in each group by putting pneumatic tourniquet on the thigh. Blood samples and skeletal muscles were collected from the rats. Plasma concentrations of glucose and insulin were measured. Insulin binding to insulin receptors was determined in skeletal muscle. RESULTS: A clear reduction of insulin binding to receptor was found in the group of animals without ischemia and the group supplemented with L-arginine and subjected to 4-h ischemia and 30- and 120-min reperfusion. A significant increase in insulin level was found in groups of animals with L-arginine and/or L-NAME subjected to 4-h ischemia at all times of reperfusion. Supplementation with L-arginine and/or L-NAME decreased levels of glucose in blood serum of animals undergoing ischemia-reperfusion syndrome compared to the control and placebo groups. CONCLUSION: Under conditions of ischemia-reperfusion, short-term administration of L-arginine causes a decrease in insulin binding capacity of insulin receptors in skeletal muscle, an increase in insulin level and a decrease in the concentration of glucose in blood serum.

The results of prolonged action of GLP-1 on some metabolic parameters.

Glucagon-like peptide (GLP-1) is widely considered as a potential drug against diabetes mellitus and obesity. It strongly stimulates the pancreas to produce and release insulin, even a few minutes after meal consumption. Because of this action, GLP-1 has been called an "incretin hormone". Moreover, GLP-1 decreases the level of glucose in the blood, independently of insulin. An obstacle to clinical application is the very short half-time of GLP-1 degradation by dipeptidyl-peptidase IV in the blood. This research was aimed at tracing all possible changes evoked by long-term application of GLP-1 in rats and comparison of two methods of application: osmotic minipumps and daily injections. In the 13-day experiment, samples of blood, muscle and liver from 24 male Wistar rats were used. Analysis included glycogen, glucose, triglycerides, free fatty acids, cholesterol, triiodotyronin, thyroxin, insulin and glucagon concentrations. The results show a lack of significant differences between both methods of application. We suggest this may be evoked by adaptation of the organism to the prolonged action of GLP-1.

In vivo investigations of neurotensin receptors in adipocytes, hepatocytes and enterocytes of rat.

INTRODUCTION: Atherosclerotic vascular disease is currently the biggest threat and the highest cause of death worldwide, approaching almost 60%.The development of atherosclerosis is affected by ecological factors associated with industry and pollution of the environment. Neurotensin (NT) is a peptide acting via 3 kinds of neurotensin receptors (NTR) localized in target tissues. In several studies, the presence of its receptors has been shown in chicken liver, and the influence of NT on the metabolism of this organ was confirmed (glycogenolysis stimulation through sympathetic nervous system, enterohepatic circulation of bile acids, metabolism of lipoproteins). MATERIALS AND METHODS: Healthy male WISTAR rats weighing 300}30 grams, were used for the experiments. The animals were divided into 4 groups: 1) control group, to which 0.9% NaCl was administrated (i.p.); 2) the second group was given levocabastine 1mg/kg i.p.; 3) the third group received SR 48692 0.4 mg/; 4) the fourth group was given NT analog [D-Trp 11]-neurotensin 15 nM/kg. Plasmatic membranes of liver, small intestine and adipose tissue were prepared according to the method of Havrankova. Analysis of results obtained in the investigation of NT receptors was performed using the Scatchard method from LIGAND-Pc, v. 3.1 software. RESULTS: The investigation of antigenity of I125NT showed proper antigen-antibody reaction. No binding of the I125NT with plasmatic membranes of adipocytes or enterocytes was observed. Unspecific binding of I125NT with 10 µmol/L of free NT was observed in the plasmatic membranes of hepatocytes. CONCLUSION: The presence of NT receptors only in the membranes of hepatocytes may suggest their role in the regulation of lipid metabolism via receptor ­ ligand way.

Evaluation of insulin binding and signaling activity of newly synthesized chromium(III) complexes in vitro.

In the present study, the influence of chromium(III) complexes (acetate, chloride, glycinate, histidinate, lactate and propionate) on insulin binding and signal transduction [phosphorylation of tyrosine and serine in the insulin receptor substrate (IRS)-1] was investigated in vitro using three experimental models: isolated rat liver membranes and cultured mouse C2C12 myoblasts or 3T3-L1 preadipocytes. The examined complexes did not elevate the binding of insulin to the liver membranes. Moreover, chromium histidinate, lactate, acetate and propionate complexes diminished the specific binding of insulin. Simultaneously, chromium chloride, which did not significantly elevate insulin binding, increased the number of membrane accessible particles of the insulin receptors. However, it was accompanied by slightly diminished affinity of the receptor to the hormone. Chromium acetate and propionate significantly diminished the binding capacity of the low-affinity insulin receptor class. Investigations with the myoblast cell line C2C12 and preadipocyte cell line 3T3-L1 did not allow differentiation of the influence of the examined complexes on insulin binding. Immunodetection of phosphorylated forms of IRS-1 showed that the chromium compounds modulated the transduction of the insulin signal. Chromium glycinate, acetate and propionate decreased the amount of IRS-1 phosphorylated at serine. Since it is generally thought that phosphorylation of serine in IRS-1 may moderate insulin action, the above mentioned chromium complexes may, in this way, enhance insulin effects inside target cells. Phosphorylation of tyrosine in IRS-1, which acts as a stimulatory signal for further steps of insulin action, was elevated after the incubation of 3T3-L1 cells with insulin. Chromium supplementation did not additionally intensify this process. However, in the absence of insulin, chromium glycinate and acetate slightly elevated the level of IRS-1 phosphorylated at tyrosine. This fact may be important in vivo at low levels of insulin in blood. The results indicate that the action of chromium(III) complexes involves a direct effect on the number of receptors accessible to insulin, their affinity to the hormone and the modulation of the signal multiplying proteins by their phosphorylation.

The level of selected hormones in peripheral blood in female polar foxes (Alopex lagopus L.) in relation to age.

The objective of the study was to determine the concentration profile of selected hormones in the blood serum of blue polar fox vixens at various ages during the non-mating period, three months after lactation. The investigation was performed on 50 clinically healthy female polar foxes derived from a domestic reproductive farm. The animals were divided into 5 age groups (n = 10) ranging from the 1 to 5 years of life. In the blood serum the contents of insulin, triiodothyronine (total and free), thyroxin (total and free), leptin and ghrelin (total and active) were determined. No significant, female age-dependent differences were found in the contents of insulin, total and free triiodothyronine and total ghrelin in the blood serum. Significant (P < 0.05) differences were observed in the concentration of total and free thyroxin (the highest in the blood of 4-year old females) as well as leptin and active ghrelin (the lowest and the highest content in 3-year old vixens). However, no distinct, female age-dependent tendencies for change in the content of these hormones in the blood serum were observed.

Changes in the content of major proteins and selected hormones in the blood serum of piglets during the early postnatal period.

The aim of the study was to determine the changes in the content of major proteins, glucose and selected hormones in the blood of piglets during the first 7 days of neonatal life. The study involved an entire litter of eight newborn piglets of F1 hybrids (Polish White Large x Polish Landrace) delivered from one sow in the second gestation. In blood samples collected directly after parturition (before colostrum intake), in the 12th, 24th and 48th hour and in 7th day of life, the content of total protein and its fractions, glucose concentration and the level of insulin, T3 (total and free), T4 (total and free), leptin, resistin and ghrelin (total and active) was determined. In the blood serum of newborn piglets a low content of total protein, albumins, gamma globulins and a high share of alpha- and beta globulins was found. In the 12th hour of life, after colostrum intake, a significant (P<0.05) increase in the content of total protein, albumins, beta-globulins and a rapid increase of gamma globulins as well as decrease of alpha-globulins level were observed. In the consecutive periods of postnatal life a significant (P<0.05) decrease of total protein, beta- and gamma globulins as well as a steady increase in the content of albumins in the blood serum of piglets was observed. The content of glucose, insulin, leptin, resistin and ghrelin in the blood serum of neonates increased significantly (P<0.05) after colostrum intake. During the successive experimental periods a progressive increase (P<0.05) of glucose and T3 as well as systematic decrease of insulin, T4, ghrelin and resistin in the blood serum was observed as compared to the 12th hour of life.

Evidence that orexins A and B stimulate insulin secretion from rat pancreatic islets via both receptor subtypes.

Orexins are recently identified neuropeptides that appear to play a role in the regulation of energy homeostasis and arousal. They bind to and activate two closely related G protein-coupled receptors (OXR1 and OXR2), previously described as orphans. In this study we examined involvement of orexins in regulation of insulin secretion from rat pancreatic islets utilizing an in situ perfused pancreas and isolated pancreatic islet models. By means of RT-PCR we found that both OXR1 and OXR2 are expressed in rat pancreatic islets. Furthermore, the expression levels of OXR1 were higher than OXR2. In both experimental models applied, orexins A and B (1, 10 and 100 nmol/l) concentration dependently stimulated insulin secretion at two different glucose concentrations (6.66 or 26.4 mmol/l), with orexin A being more potent than orexin B. This study demonstrates that orexins A and B modulate insulin secretion in vitro.

The influence of glimepiride on the binding kinetics of insulin with its skeletal muscle and liver receptors in rats with short term and prolonged hyperglycemia induced by streptozotocin.

BACKGROUND: The aim of the study was to determine the influence of glimepiride on the binding kinetics of insulin with its skeletal muscle receptor in rats with transient and prolonged hyperglycemia induced by streptozotocin. MATERIAL/METHODS: The studies were performed on healthy male Wistar rats with a body mass of 220+/-30 g, fed with LSM-type standard chow, and given water ad libitum. Transient or prolonged hyperglycemia was induced by intraperitoneal administration of streptozotocin. Blood samples were taken from the right heart ventricle to heparinized test tubes and centrifuged for 10 minutes at 700 i. g. Plasma was collected and the glucose level was determined. From each animal 1 g of skeletal muscle and 1 g of liver were collected as well, placed in liquid nitrogen and stored until determination of the affinity and number of receptors. RESULTS: We found an increase in affinity and binding capacity of high- and low-affinity receptors in rats with both transient and prolonged streptozotocin-induced hyperglycemia. The affinity and binding capacity of receptors increased under the influence of glimepiride in transient hyperglycemia caused by streptozotocin administration. CONCLUSIONS: The affinity and binding capacity of receptors increased under the influence of glimepiride in the course of transient hyperglycemia. The lack of changes in the specific insulin binding and binding capacity of receptors of both low and high affinity in the group of animals with prolonged hyperglycemia requires explanation.

In vivo and in situ action of melatonin on insulin secretion and some metabolic implications in the rat.

INTRODUCTION: The role of melatonin in human insulin regulation is poorly understood. AIM: To investigate the influence of melatonin supplementation on glucose and insulin levels and on lipid metabolism in blood serum and the liver. METHODOLOGY: The acute melatonin effects on insulin secretion in male Wistar rats were investigated. In addition, carbohydrate and lipid metabolism was studied. In in vivo experiments, melatonin was administered subcutaneously in two different doses (0.5 and 1.0 mg/kg body weight, respectively), and animals were decapitated after 1 hour. RESULTS: The higher dose of the hormone increased insulin level in blood. The applied pancreas perfusion technique allowed us to confirm a direct mechanism of melatonin action on the pancreas. The ability of melatonin to stimulate insulin output was dose dependent. The highest effect was noticed for 100 nmol/L, whereas 1 nmol/L did not influence this process. CONCLUSION: Melatonin treatment in vivo caused many biochemical consequences. The hormone augmented significantly the concentrations of total, free, and esterified cholesterol, as well as high-density lipoprotein cholesterol in blood. Together with the enhanced insulin secretion observed in the in vivo experiment, the level of free fatty acids in blood decreased and, surprisingly, glucose concentration was significantly elevated.

Rat thyroid gland expresses the long form of leptin receptors, and leptin stimulates the function of the gland in euthyroid non-fasted animals.

Leptin is an adipose tissue-secreted hormone, which decreases caloric intake and increases energy expenditure. Some effects of leptin on energy balance seem to be mediated by the hypothalamo-pituitary-thyroid axis. The present study was designed to ascertain whether i) rat thyroid gland expresses the long form of leptin receptor (ObRb) and ii) the prolonged leptin administration (daily subcutaneous injections of 24 nmol/kg leptin for 6 consecutive days) affects thyroid-gland function in this species. Coupled RT-PCR, Western blotting and immunocytochemical findings demonstrated the expression of Ob-Rb as mRNA and protein in the thyroid gland of normal rats. Prolonged leptin treatment raised thyroid-gland weight, and morphometry showed that in the enlarged glands the volume of the follicle epithelium was increased, while that of colloid remained unchanged, so that epithelium/colloid ratio was markedly lowered. In leptin-administered rats, the plasma concentration of TSH was decreased, while those of thyroid hormones (free T3 and total T4) were notably raised. Collectively, these findings suggest that systemically administered leptin stimulates growth and secretion of thyroid gland in the rat, through a direct mechanism involving Ob-Rb.