THE IMPACT OF TYPE 2 DIABETES ON THE CARDIOVASCULAR SYSTEM IN MALE AND FEMALE RATS

Type 2 diabetes mellitus (T2DM) is a noncommunicable and the one of the fastest growing disease that affects millions of people worldwide. Compared to the general population, individuals with type 2 diabetes are at an increased risk of cardiovascular disease (CVD) [1]. While CVD is a leading cause of death in both women and men, accumulating evidence suggest that biological sex is a major determinant for the development and progression of CVD. Women with T2DM have been reported to have significantly higher risks of both fatal and non-fatal coronary heart disease and stroke than men with diabetes [2–6]. The Framingham Heart Study first revealed that diabetic women have a 5.1-fold increase in heart failure, while diabetic men only have a 2.4-fold increase compared to non-diabetic women and men, respectively [7]. It is hypothesized that diabetes mellitus (DM) attenuates the general female biological advantage of protecting against cardiovascular complications. These mechanisms include the altered systemic glucose regulation and lower insulin sensitivity, more pronounced hypertension, elevated triglycerides, inflammation and higher prothrombotic profile in females compared to males [8]. Sex differences in body composition and fat distribution may be involved in prevalence of over-weight and obesity in women and therefore increase CVD risk [9]. Additionally, estrogen-related signalling within the female myocardium plays important role both in protection and in progression of DM and its complications. Many risk factors probably contribute discrepancies in cardiovascular complications between men and women [9]. Moreover, diabetic females feature greater susceptibility to diabetic cardiomyopathy then

Type 2 diabetes mellitus (T2DM) is a noncommunicable and the one of the fastest growing disease that affects millions of people worldwide. Compared to the general population, individuals with type 2 diabetes are at an increased risk of cardiovascular disease (CVD) [1]. While CVD is a leading cause of death in both women and men, accumulating evidence suggest that biological sex is a major determinant for the development and progression of CVD.
Women with T2DM have been reported to have significantly higher risks of both fatal and non-fatal coronary heart disease and stroke than men with diabetes [2][3][4][5][6]. The Framingham Heart Study first revealed that diabetic women have a 5.1-fold increase in heart failure, while diabetic men only have a 2.4-fold increase compared to non-diabetic women and men, respectively [7].
It is hypothesized that diabetes mellitus (DM) attenuates the general female biological advantage of protecting against cardiovascular complications. These mechanisms include the altered systemic glucose regulation and lower insulin sensitivity, more pronounced hypertension, elevated triglycerides, inflammation and higher prothrombotic profile in females compared to males [8]. Sex differences in body composition and fat distribution may be involved in prevalence of over-weight and obesity in women and therefore increase CVD risk [9].
Additionally, estrogen-related signalling within the female myocardium plays important role both in protection and in progression of DM and its complications. Many risk factors probably contribute discrepancies in cardiovascular complications between men and women [9].
Moreover, diabetic females feature greater susceptibility to diabetic cardiomyopathy then * The manuscript was performed in accordance with the scientific theme of the biochemical research laboratory in the SI «V. Danilevsky Institute for Endocrine Pathology Problems of the NAMS of Ukraine» «The determination of biochemical and functional disorders that cause sexual dimorphism of major cardiovascular risk factors of type 2 diabetes mellitus» (state registration №0116U000332).
The financing source of the work is the National Academy of Medical Sciences of Ukraine. The author assume responsibility for the published work. The author guarantee absence of competing interests and their own financial interest when carrying out the research and writing the article.
The manuscript was received by the editorial staff 16.03.2020.
Проблеми ендокринної патології № 3, 2020 Експериментальні дослідження males due to more pronounced cardiac structural remodelling and development of diastolic dysfunction. Furthermore, female sex is the only independent predictor of left ventricular hypertrophy [10]. However, how T2DM modulates this effect in the heart tissues of women versus men is currently unclear. Future research leading to determination of these mechanisms may contribute to sex-specific treatment for diabetic macro-vascular disease.
The aim of this study was to determine the impact of type 2 diabetes on the functional state of the cardiovascular system in male and female rats.

MATERIALS AND METHODS
The present study was approved by the bioethics committee of the V. Danilevsky Institute of Endocrine Pathology Problems, National Academy of Medical Sciences of Ukraine (Kharkiv, Ukraine) and performed in accordance with the European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes (Strasbourg, 1986).
The experiments were performed on Wistar rats, which were housed in Plexiglas cages at a temperature of (22 ± 1)°C, in a constant 12-hour light/dark cycle.
The animal model of type 2 diabetes (T2D) induced by a high-caloric diet, combined with multiple low-dose streptozotocin (STZ) injections, was used. The control intact groups (n = 6) were fed a standard diet ad libitum du ring 14 weeks. The experimental groups (n = 6) were fed the high-caloric diet, contain-ing 16 % fat, 28 % carbohydrates, 6 % proteins for 14 weeks. All groups had free access to water. In four weeks, rats in the experimental group were injected intraperitoneally with small doses of STZ (25 mg/kg body weight) twice per week [11].
At the end of the study electrocardiograms were recorded in leads II using the electrocardiography method. The mean R-R, Q-T, Р-Q, QRS, T-Р intervals and the amplitude and duration of T, P and R waves were calculated.
Data normality were rated using the Shapiro-Wilk test, and all normally distributed data are expressed as the means ± standard error of the mean (SEM). Group comparisons of quantitative variables were performed by one-factor analysis of variance (ANOVA). The Newman-Keuls test was used for multiple comparisons of the groups. Values were considered significant at p < 0.05.

RESULTS AND DISCUSSION
As shown in Table 1, the basal glucose level in diabetic rats was significantly higher in comparison with control rats. In addition, the level of basal hyperglycaemia in diabetic animals was independent from sex.
In our study T2D caused an increase in heart rate, as indicated by the shortening of R-R interval, in both female and male rats in comparison with intact control groups (see table 2).
The results indicate the development of pathologically accelerated rhythm and sinus tachycardia in experimental animals of both sexes.
It has been established that T2D leads to the prolongation of electrical systole occurs as the result of an increase in action potential duration in both males and females, as evidenced by an increasing of the total length Q-T intervals, compared to control group's data (see table 2). It was found that the duration of P-Q interval reflected the signal conduction from the sinus to the contractile ventricular myocardium, was probably higher in both intact females and T2D females versus intact and diabetic males (see table 2). However, T2D did not change the duration of P-Q interval in animals of both sexes, indicating that there is no influence of this model of diabetes on the atria-ventricular conduction.
Our results have shown that T2D promotes the development of diastolic dysfunction in females, in contrast to males. Our study clearly points out the signs of diastolic dysfunction such as prolongation of diastolic T-P interval and a decrease of amplitude and duration of the T wave, which reflects the processes of ventricular myocardial repolarization, in comparison with intact female rats (see table 2 and table 3).
The findings are referred to clinical data on the higher prevalence of diastolic dysfunction and/ or left ventricular hypertrophy, as a structural and functional component of diabetic cardiomyopathy, in women than in men [12].
T2D was accompanied by multidirectional impact on the impairment of atrial activation in heart of both sexes rats. Thus, females were showed an increase of the P wave' amplitude compare to intact control, which may be explained by the development of hypertrophic processes in the atria. Decreased the P wave' amplitude was noted in males possibly due to the progress of ischemia in the myocardium (see table 3).
It has been established that duration of the R-wave doesn't change in any of the experimental groups, but R-waves voltage is decreased only in male rats with T2D in comparison with   Introduction. Type 2 diabetes mellitus is one of the main factors of the cardiovascular risk, which leads to a disproportionate increase in cardiovascular events in women and men. While the greater excess risk of diabetic vascular complications in women compared with men has been described, mechanisms underpinning the sex difference have not been identified in full.

duration of R-R, Q-T, Р-Q, QRS and T-Р intervals in control and diabetic rats, (X ± S X ), n = 6
The aim of this study was to determine the impact of type 2 diabetes (T2D) on the functional state of the cardiovascular system in male and female rats.
Materials and Methods. T2D was induced in male and female Wistar rats by a high-caloric diet during 14 weeks combined with intraperitoneal injections of 25 mg/kg streptozotocin twice per week. At the end of the study electrocardiograms were recorded in leads II. A comparative analysis of changes in the functional state of the heart in male and female rats with experimental T2D was conducted.
Results. It was established that T2D, independently of gender, results in the formation of pathologically accelerated rhythm and sinus tachycardia in experimental animals. Experimental T2D led to the prolongation of the systole in rats of both sex and decreasing of R-wave voltage in males in comparison with control group. In addition, T2D was accompanied by multidirectional impact on the atrial function in the heart of both sexes: P wave' amplitude was increased in females while it was decreased in males, what can indicate either right or left atrial enlargement. It was found that T2D promotes the development of myocardial diastolic dysfunction in females, in contrast to males, which was confirmed by prolongation of T-P interval and a decrease of amplitude and duration of the T wave in comparison with intact female rats.
Conclusions. T2D, independently of gender, caused cardiac arrhythmias, functional changes in atrial and ventricular conduction, but only in females, in contrast to males, was accompanied by the development of myocardial diastolic dysfunction. This data justify the necessity of personalized-and gender-specific therapy development for the prevention and management of diabetic cardiovascular complications.
K e y w o r d s : type 2 diabetes, functional state of the cardiovascular system, sex differences, rats.