Persistence of inflammatory response to intense exercise in diabetic rats

Chemoprotective Mechanism of Sodium Thiosulfate Against Cisplatin-Induced Nephrotoxicity Is via Renal Hydrogen Sulfide, Arginine/cAMP and NO/cGMP Signaling Pathways

Cisplatin is a common and highly effective chemotherapeutic agent whose nephrotoxic side effect is well-characterized. Sodium thiosulfate (STS), an FDA-approved hydrogen sulfide (H2S) donor drug, is emerging as a chemoprotective agent against cisplatin-induced nephrotoxicity (CIN). In this study, we investigated the chemoprotective mechanism of STS in a rat model of CIN. Twenty-five male Sprague Dawley rats were randomly assigned to the following groups: HC: Healthy control (received 10 mL/kg/day of 0.9% saline intraperitoneally (ip), [n = 5]), CIN: Cisplatin (received single dose of 7 mg/kg cisplatin ip [n = 5]); CIN + PAG: Cisplatin and daily ip administration of 40 mg/kg of the H2S inhibitor, DL-propargylglycine (PAG) for 28 days (n = 5); CIN + PAG + STS: Cisplatin and daily PAG and STS (150 µM) ip injection for 28 days; CIN + STS: Cisplatin and daily STS ip administration for 28 days (n = 5). Rats in each group were kept in metabolic cages for 24 h on day 0, 14 and 29 after cisplatin administration for urine collection. Rats were then euthanized, and kidney and blood samples were collected for analysis. Histologically, CIN was characterized by glomerular and tubular injury and significant macrophage influx and tubular apoptosis, as well as markedly increased levels of plasma and renal IL-1β, IL-6 and TNF-α and impaired renal antioxidant status compared to HC rats (p < 0.001). These pathological changes were exacerbated in CIN + PAG rats and were strongly reduced in CIN + PAG + STS rats relative to CIN + PAG rats (p < 0.01), while superior renal protection was observed in CIN + STS rats. Functionally, CIN was evidenced by markedly increased levels of serum creatinine and BUN, and significantly decreased urine creatinine, renal creatinine clearance, as well as electrolyte imbalance and urinary concentrating defect in comparison with HC (p < 0.01). These functional changes worsened significantly in CIN + PAG rats (p < 0.05) but improved in CIN + PAG + STS rats, with further improvement in CIN + STS rats to levels comparable to HC rats. Mechanistically, STS increased renal and plasma levels of H2S, arginine, cAMP, nitric oxide (NO) and cGMP as well as SIRT3 and PGC-1α. We have shown for the first time that STS provides chemoprotection against CIN by activating renal arginine/cAMP and NO/cGMP signaling pathways and their downstream mechanisms through increased renal H2S production.

Does irisin has neuroprotective effect against diabetes induced neuropathy in male rats?

We aimed to investigate the contribution of irisin in the neuroprotective process of exercise training in diabetic rats. Serum irisin levels, thermal and mechanical pain thresholds and intracellular calcium ([Ca²⁺]_i) levels in sensory neurons were measured at different time intervals during the eight weeks of exercise sessions for the control, non-exercise diabetics (3 groups) and exercise performing (low and high intensity groups) diabetic rats (n = 7-10 for all groups). Non-exercise diabetic groups were treated with irisin in different doses (1, 10 and 20 µg/kg respectively). Recovered pain thresholds at the end of the exercise sessions (p < .05), higher serum irisin levels that compared to control and diabetics (p < .05) and insignificant mean [Ca2⁺]_i peak amplitudes in sensory neurons (p > .05) obtained from experiments. Furthermore, irisin injection decreased the thermal pain threshold of diabetics only at 60th minutes (p < .05). Irisin may have a role in the neuroprotective effect of exercise training.

Alpha-lipoic acid treatment improves adverse cardiac remodelling in the diabetic heart - The role of cardiac hydrogen sulfide-synthesizing enzymes

INTRODUCTION

Alpha-lipoic acid (ALA) is a licensed drug for the treatment of diabetic neuropathy. We recently reported that it also improves diabetic cardiomyopathy (DCM) in type 2 diabetes mellitus (T2DM). In this study, we present evidence supporting our hypothesis that the cardioprotective effect of ALA is via upregulation of cardiac hydrogen sulfide (H₂S)-synthesizing enzymes.

METHODS

Following 12 h of overnight fasting, T2DM was induced in 23 out of 30 male Sprague-Dawley rats by intraperitoneal administration of nicotinamide (110 mg/kg) followed by streptozotocin (55 mg/kg) while the rest served as healthy control (HC). T2DM rats then received either oral administration of ALA (60 mg/kg/day; n = 7) or 40 mg/kg/day DL-propargylglycine (PAG, an endogenous H₂S inhibitor; n = 7) intraperitoneally for 6 weeks after which all rats were sacrificed and samples collected for analysis. Untreated T2DM rats served as diabetic control (DCM; n = 9).

RESULTS

T2DM resulted in weight loss, islet destruction, reduced pancreatic β-cell function and hyperglycemia. Histologically, DCM rats showed significant myocardial damage evidenced by myocardial degeneration, cardiomyocyte vacuolation and apoptosis, cardiac fibrosis and inflammation, which positively correlated with elevated levels of cardiac damage markers compared to HC rats (p < 0.001). These pathological alterations worsened significantly in PAG-treated rats (p < 0.05). However, ALA treatment restored normoinsulemia, normoglycemia, prevented DCM, and improved lipid and antioxidant status. Mechanistically, ALA significantly upregulated the expression of cardiac H₂S-synthesizing enzymes and increased plasma H₂S concentration compared to DCM rats (p < 0.001).

CONCLUSION

ALA preserves myocardial integrity in T2DM likely by maintaining the expression of cardiac H₂S-synthezing enzymes and increasing plasma H₂S level.

Activation of renal CSE/H2S pathway by alpha-lipoic acid protects against histological and functional changes in the diabetic kidney

INTRODUCTION

We previously reported that alpha-lipoic acid (ALA) supplementation protects against progression of diabetic kidney disease (DKD). In this study, we aim to investigate whether the mechanism of renal protection by ALA involves renal cystathionine γ-lyase/hydrogen sulfide (CSE/H₂S) system in type 2 diabetes mellitus (T2DM).

METHODS

Thirty-seven male Sprague-Dawley rats underwent 12 h of overnight fasting. To induce T2DM, 30 of these rats received intraperitoneal administration of nicotinamide (110 mg/kg) and streptozotocin (55 mg/kg). T2DM rats then received either oral administration of ALA (60 mg/kg/day) or intraperitoneal administration of 40 mg/kg/day DL-propargylglycine (PAG, a CSE inhibitor) or both for 6 weeks after which rats were sacrificed and samples collected for analysis. Untreated diabetic and non-diabetic rats served as diabetic and healthy controls respectively.

RESULTS

T2DM was characterized by reduced pancreatic β-cell function and hyperglycemia. Histologically, untreated diabetic rats showed significantly damaged pancreatic islets, glomerular and tubular injury, with elevated levels of renal function markers compared to healthy control rats (p < 0.001). These pathological changes worsened significantly following PAG administration (p < 0.05). While some renal protection was observed in ALA+PAG rats, ALA administration in untreated diabetic rats provided superior protection comparable to healthy control rats, with improved antioxidant status, lipid profile and reduced inflammation. Mechanistically, ALA significantly activated renal CSE/H₂S system in diabetic rats, which was markedly suppressed in PAG-treated rats (p < 0.001).

CONCLUSION

Our data suggest that ALA protects against DKD development and progression by activating renal CSE/H₂S pathway. Hence, CSE/H₂S pathway may represent a therapeutic target in the treatment or prevention of DKD in diabetic patients.

Supplementation of conventional anti-diabetic therapy with alpha-lipoic acid prevents early development and progression of diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Current pharmacological interventions only retard DN progression. Alpha-lipoic acid (ALA) is a potent antioxidant with beneficial effect in other diabetic complications. This study investigates whether ALA supplementation prevents early development and progression of DN.

METHOD

Fifty-eight male Sprague-Dawley rats were randomly assigned to healthy control and diabetic groups and subjected to overnight fasting. Type 2 diabetes mellitus (T2DM) was induced in diabetic group by intraperitoneal administration of nicotinamide (110 mg/kg) and streptozotocin (55 mg/kg). On day 3 after T2DM induction, diabetic rats received oral daily administration of ALA (60 mg/kg), gliclazide (15 mg/kg), ramipril (10 mg/kg) or drug combinations for 6 weeks. Untreated diabetic rats served as diabetic control. Blood, kidneys and pancreas were harvested for biochemical and histological analyses.

RESULT

Induction of T2DM resulted in hypoinsulinemia, hyperglycemia and renal pathology. ALA supplementation maintained β-cell function, normoinsulinemia and normoglycemia in diabetic rats, and prevented renal pathology (PAS, KIM-1, plasma creatinine, total protein, blood urea nitrogen, uric acid and urine albumin/creatinine ratio) and triglycerides level compared to diabetic control (p < 0.001). Additionally, ALA supplementation significantly prevented elevated serum and tissue malondialdehyde, collagen deposition, α-SMA expression, apoptosis and serum IL-1β and IL-6 levels while it markedly increased renal glutathione content and plasma HDL-C compared to diabetic control group (p < 0.001).

CONCLUSION

ALA supplementation prevents early development and progression of DN by exerting anti-hyperglycemic, antioxidant, anti-inflammatory, anti-fibrotic and anti-apoptotic effects. Our findings provide additional option for clinical treatment of DN in T2DM patients.

Combination Therapy of Alpha-Lipoic Acid, Gliclazide and Ramipril Protects Against Development of Diabetic Cardiomyopathy via Inhibition of TGF-β/Smad Pathway

Background: Diabetic cardiomyopathy (DCM) is a major long-term complication of diabetes mellitus, accounting for over 20% of annual mortality rate of diabetic patients globally. Although several existing anti-diabetic drugs have improved glycemic status in diabetic patients, prevalence of DCM is still high. This study investigates cardiac effect of alpha-lipoic acid (ALA) supplementation of anti-diabetic therapy in experimental DCM. Methods: Following 12 h of overnight fasting, 44 male Sprague Dawley rats were randomly assigned to two groups of healthy control (n = 7) and diabetic (n = 37) groups, and fasting blood glucose was measured. Type 2 diabetes mellitus (T2DM) was induced in diabetic group by intraperitoneal (i.p.) administration of nicotinamide (110 mg/kg) and streptozotocin (55 mg/kg). After confirmation of T2DM on day 3, diabetic rats received monotherapies with ALA (60 mg/kg; n = 7), gliclazide (15 mg/kg; n = 7), ramipril (10 mg/kg; n = 7) or combination of the three drugs (n = 7) for 6 weeks while untreated diabetic rats received distilled water and were used as diabetic control (n = 9). Rats were then sacrificed, and blood, pancreas and heart tissues were harvested for analyses using standard methods. Results: T2DM induction caused pancreatic islet destruction, hyperglycemia, weight loss, high relative heart weight, and development of DCM, which was characterized by myocardial degeneration and vacuolation, cardiac fibrosis, elevated cardiac damage markers (plasma and cardiac creatine kinase-myocardial band, brain natriuretic peptide and cardiac troponin I). Triple combination therapy of ALA, gliclazide and ramipril preserved islet structure, maintained body weight and blood glucose level, and prevented DCM development compared to diabetic control (p < 0.001). In addition, the combination therapy markedly reduced plasma levels of inflammatory markers (IL-1β, IL-6 and TNF-α), plasma and cardiac tissue malondialdehyde, triglycerides and total cholesterol while significantly increasing cardiac glutathione and superoxide dismutase activity and high-density lipoprotein-cholesterol compared to diabetic control (p < 0.001). Mechanistically, induction of T2DM upregulated cardiac expression of TGF-β1, phosphorylated Smad2 and Smad3 proteins, which were downregulated following triple combination therapy (p < 0.001). Conclusion: Triple combination therapy of ALA, gliclazide and ramipril prevented DCM development by inhibiting TGF-β1/Smad pathway. Our findings can be extrapolated to the human heart, which would provide effective additional pharmacological therapy against DCM in T2DM patients.

Resistance exercise shifts the balance of renin-angiotensin system toward ACE2/Ang 1-7 axis and reduces inflammation in the kidney of diabetic rats

AIMS

We aimed to determine whether resistance training (RT) regulates renal renin-angiotensin system (RAS) components and inflammatory mediators in diabetic rats.

MAIN METHODS

Male Wistar rats (3 months old) were randomly assigned into four groups: non-trained (NT), trained (T), non-trained + diabetes (NTD) and trained +diabetes (TD). Diabetes was induced by streptozotocin (50 mg/kg, Sigma Chemical Co., St. Louis, MO, USA), before RT protocol. Trained rats performed RT protocol on a 110-cm ladder (8 ladder climbs, once/day, 5 days/week, 8 weeks), carrying a load corresponding to 50-80% of maximum carrying capacity. Blood glucose, albuminuria and urinary volume were measured. Renal levels of angiotensin peptides (angiotensin I, II and 1-7), inflammatory markers, and also the activities of angiotensin-converting enzyme (ACE) and ACE2 were determined.

KEY FINDINGS

Blood glucose and urinary volume were elevated in diabetic animals, and RT decreased albuminuria, renal Ang I and Ang II levels in diabetic rats. RT shifted the balance of renal RAS toward ACE2/Ang 1-7 axis in TD group, and mitigated the high levels of interleukin (IL)-10, IL-1β and cytokine-induced neutrophil chemoattractant 1 (CINC) in the context of diabetes. Strong positive correlations were found between albuminuria and Ang II, IL-10 and IL-1β. On the other hand, intrarenal Ang 1-7 levels were negatively correlated with IL-10 and IL-1β levels.

SIGNIFICANCE

RT improved kidney function by modulating intrarenal RAS toward ACE2/Ang 1-7 axis and inflammatory cytokines. RT represents a reasonable strategy to improve the renal complications induced by diabetes, counteracting nephropathy-associated maladaptive responses.

Blood lipid profile changes in type 2 diabetic rats after tail suspension and reloading

Purpose

The effects of the tail suspension and reloading on the protein and lipid metabolism in muscle and blood in type 2 diabetes mellitus (T2DM) are unclear. This study evaluated the hypothesis that skeletal muscle catabolism is greater in T2DM than in non-diabetes mellitus (non-DM) rats and that the activity-dependent changes in the intramuscular lipid accumulation and blood lipid profile are poorer in T2DM than in non-DM rats.

Methods

T2DM and non-DM rats were suspended for two weeks followed by reloading for two weeks. The muscle and blood were then examined.

Results

In contrast to our hypothesis, there was no marked difference between the T2DM and non-DM groups in terms of the skeletal muscle catabolism and activity-dependent changes in intramuscular lipid accumulation. However, the blood lipid profile increased in the T2DM group compared to the non-DM group. One interesting finding in this study was the decrease in non-high-density lipoprotein (non-HDL) cholesterol levels after one week of reloading followed by a significant increase in the non-HDL cholesterol levels after two weeks of reloading in the T2DM group.

Conclusion

These results suggest that a dramatic increase in activity after a period of inactivity may rapidly improve the blood lipid profile in T2DM rats.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01511-y.

Melatonin improves the antioxidant capacity in cardiac tissue of Wistar rats after exhaustive exercise

We investigated the effects of melatonin on the onset and resolution of the oxidative stress in the cardiac muscle in melatonin-treated and nontreated rats subjected to an exhaustive exercise session. Forty male rats were divided into: melatonin-treated (20 mg/kg supplemented for 10 d) and control. On the 10th day, each group was subdivided according to euthanasia moments: control or melatonin-treated not exercised (C0h and M0h); immediately after the exercise (CIA and MIA); and 2 h after exercise (C2h and M2h). The heart of animals was removed and the levels of oxidative stress index (OSI) and the formation of thiobarbituric acid reactive substances (TBARS), protein carbonyl, and the activities of aconitase, catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were evaluated. Total antioxidant status (TAS), total oxidant status (TOS), and the protein expression of CAT, GPx, and SOD was also measured. Our data revealed significant differences on: (i) OSI (p=.029), CAT activity (p=.016), CAT content (p<.001), GPx content (p=.014), reduced glutathione levels (p<.001), and aconitase activity (p<.001) for interaction of melatonin; (ii) GPx activity (p=.005), reduced glutathione (p=.004), protein carbonyl (p=.035), and TBARS levels (p=.028) between groups, and (iii) TBARS levels (p=.016) for significance between moments. Although the exhaustive exercise protocol imposed mild oxidative stress on the cardiac tissue of rats, melatonin induced antioxidant responses that rebalanced the redox status of the cardiac tissue, especially after exhaustive exercise.

Recovery of Diabetic Rats After Physical Exhaustion: Kinetic Alterations in Muscle Inflammation and Muscle-Signaling Proteins to Atrophy and Hypertrophy

The complexity of the adaptive response of diabetics to intense exercise is still poorly understood. To optimize exercise interventions in diabetics, the chronology of inflammatory mediators in muscle and the signaling involved in muscle hypertrophy/atrophy must be understood. Herein, we studied the kinetic inflammatory profile and cellular signaling pathways modulated by physical exhaustion after the induction of type 1 diabetes by streptozotocin in rats. Soleus muscle samples were obtained from diabetic and control groups at the following moments: baseline (no exercise); immediately after exhaustive exercise; and at 2 h, 24 h, 48 h, and 72 h after a treadmill exhaustive exercise. Kinetic production of cytokines and kinetic activation of proteins related to muscle synthesis (p70S6K and Akt) and degradation (GSK3, MuRF1, and MAFbx) were measured in the soleus muscle. We observed that the muscle TNF-α (0.9-fold; p = 0.0007), IL-1β (0.8-fold; p = 0.01), IL-6 (0.8-fold; p = 0.0013), L-selectin (1.0-fold; p = 0.0019), and CINC-2α/β (0.9-fold; p = 0.04) levels were higher in almost all stages of the study in the diabetic animals compared with the control group. Our data showed that exhaustive exercise decreased MAFbx expression in diabetic animals compared to the control group in a time-dependent manner. The decreased activation ratios of MAFbx were followed by a decrease in TNF-α, IL-1β, and IL-6 levels. p70S6k phosphorylation was also decreased in the diabetic group compared to the control group after physical exhaustion. Regarding the activation of proteins related to muscle synthesis and degradation, we found that the alterations induced by exhaustive exercise in the diabetic rats might involve pathways related to synthesis and muscle breakdown. Moreover, after an exhaustive exercise session, the recovery of the inflammatory response in the diabetic animals was slower than that in the control rats while the return of inflammatory cytokines to baseline levels was more effective in the diabetic animals.

Moderate and high intensity chronic exercise reduces plasma tumor necrosis factor alpha and increases the Langerhans islet area in healthy rats

OBJECTIVE

This study aimed to examine the effects of moderate (MIT) and high-intensity training (HIT) chronic exercise on plasma tumor necrosis factor alpha (TNF-α) level and its impact on Langerhans islet morphology in healthy rats.

METHODS

Two-month old normal male Wistar rats were divided into three groups: control (C, n=6), MIT (n=6), and HIT (n=4). The training protocol consisted in 24 sessions of running on a treadmill at 60-80% maximal oxygen consumption (VO_2max) for MIT, and >80% VO_2max for HIT. TNF-α and insulin were measured with ELISA tests. Duodenal pancreas was dissected to analyze the Langerhans islets by immunohistochemistry, a correlation analysis was performed with the nuclei/total islet area. Results: HIT and MIT rats showed lower TNF-α plasma levels than controls. Plasma insulin level decreased significantly in HIT compared with C and MIT. In addition, the islet area and nuclei density per islet were higher in the exercise groups compared with C. However, none of the groups showed PD1 immunoreactivity.

CONCLUSIONS

Under healthy conditions, the chronic exercise reduced plasmatic TNF-α level, and in the same sense, increased the size of the Langerhans islets, depending to the exercise intensity.

Advances in the Use of Stem Cells in Veterinary Medicine: From Basic Research to Clinical Practice

Today, several veterinary diseases may be treated with the administration of stem cells. This is possible because these cells present a high therapeutic potential and may be injected as autologous or allogenic, freshly isolated, or previously cultured. The literature supports that the process is safe and brings considerable benefits to animal health. Knowledge about how adult stem cells modulate the molecular signals to activate cell homing has also been increasingly determined, evidencing the mechanisms which enable cells to repair and regenerate injured tissues. Preclinical studies were designed for many animal models and they have contributed to the translation to the human clinic. This review shows the most commonly used stem cell types, with emphasis on mesenchymal stem cells and their mechanistic potential to repair, as well as the experimental protocols, studied diseases, and species with the highest amount of studies and applications. The relationship between stem cell protocols utilized on clinics, molecular mechanisms, and the physiological responses may offer subsidies to new studies and therefore improve the therapeutic outcome for both humans and animals.

Myotubes from lean and severely obese subjects with and without type 2 diabetes respond differently to an in vitro model of exercise

Exercise improves insulin sensitivity and oxidative capacity in skeletal muscles. However, the effect of exercise on substrate oxidation is less clear in obese and type 2 diabetic subjects than in lean subjects. We investigated glucose and lipid metabolism and gene expression after 48 h with low-frequency electrical pulse stimulation (EPS), as an in vitro model of exercise, in cultured myotubes established from lean nondiabetic subjects and severely obese subjects (BMI ≥ 40 kg/m2) with and without type 2 diabetes. EPS induced an increase in insulin sensitivity but did not improve lipid oxidation in myotubes from severely obese subjects. Thus, EPS-induced increases in insulin sensitivity and lipid oxidation were positively and negatively correlated to BMI of the subjects, respectively. EPS enhanced oxidative capacity of glucose in myotubes from all subjects. Furthermore, EPS reduced mRNA expression of slow fiber-type marker (MYH7) in myotubes from diabetic subjects; however, the protein expression of this marker was not significantly affected by EPS in either of the donor groups. On the contrary, mRNA levels of interleukin-6 (IL-6) and IL-8 were unaffected by EPS in myotubes from diabetic subjects, while IL-6 mRNA expression was increased in myotubes from nondiabetic subjects. EPS-stimulated mRNA expression levels of MYH7, IL-6, and IL-8 correlated negatively with subjects' HbA1c and/or fasting plasma glucose, suggesting an effect linked to the diabetic phenotype. Taken together, these data show that myotubes from different donor groups respond differently to EPS, suggesting that this effect may reflect the in vivo characteristics of the donor groups.

Melatonin decreases muscular oxidative stress and inflammation induced by strenuous exercise and stimulates growth factor synthesis

Strenuous exercise is detrimental to athletes because of the overproduction of reactive oxygen species. Melatonin, a classic antioxidant, has been shown to exhibit beneficial effects regarding intense exercise and tissue repair. In this study, we evaluated the onset and resolution of inflammation in melatonin-treated and nontreated rats subjected to a strenuous exercise session. We also analyzed the formation of thiobarbituric acid reactive substances (TBARS) and the activities of catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD). Control and treated rats were subjected to exhaustive exercise after a period of 10 days of melatonin treatment (20 mg/dL). Plasma and muscle levels of tumor necrosis factor-alpha (TNF-α), interleukin 1 beta (IL-1β), interleukin 6 (IL-6), cytokine-induced neutrophil chemoattractant-2-alpha/beta (CINC-2α/β), l-selectin, macrophage inflammatory protein-3-alpha (MIP-3α), and vascular endothelial growth factor (VEGF) were measured prior to, immediately after, and 2 hr after exercise. Our data revealed decreases in the muscle concentrations of IL-1β (35%), TNF-α (13%), IL-6 (48%), and TBARS (40%) in the melatonin-treated group compared with the control group. We also observed decreases in the plasma concentrations of IL-1β (17%) in the melatonin-treated group. VEGF-α concentrations and SOD activity increased by 179% and 22%, respectively, in the melatonin-treated group compared with the control group. We concluded that muscle inflammation and oxidative stress resulting from exhaustive exercise were less severe in the muscles of melatonin-treated animals than in the muscles of control animals. Thus, melatonin treatment may reverse exercise-induced skeletal muscle inflammation and stimulate growth factor synthesis.

Morphology and Contractility of Cardiac Myocytes in Early Stages of Streptozotocin-Induced Diabetes Mellitus in Rats

Diabetic cardiomyopathy is the leading cause of mortality in type 1 diabetes. Thus study of cardiomyocyte morphology and function during early stages of diabetes using modern analytical methods is of critical importance. Therefore, using confocal microscopy, we determined metric parameters, volumes and contractility, with calcium transients in isolated left-ventricular myocytes at one week after induction of diabetes in rats. Myocyte volume analysis from 3D confocal scans was performed using an automated contour detection algorithm that took the actual shape of the myocytes into account. We showed a significant reduction in myocyte volume in diabetic animals. We also showed a significant reduction in length and width but not in thickness of the myocytes, which suggests disproportional reorganization of the structure of the heart tissue during short-term diabetes. From a functional point of view, we observed a significant decrease in cell shortening at a stimulation frequency of 0.5 Hz. This was accompanied by a decrease in calcium transient amplitude. Together, these data suggest that impaired calcium handling is one of the factors that contributes to the observed decrease in myocyte shortening during early stages of streptozotocin-induced diabetes in rats.