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Background: The aim of the study is to define the possibility of usage of the gene eNOS polymorphisms as molecular-genetic markers of athletes’ resistance to exercise-induced hypoxia. Material/Methods: 127 highly qualified athletes were examined (30 persons are underwater finswimmers, 41 – rowers and 56 sportsmen who practice speed and power track and field exercises). The frequency of promotor polymorphisms and the 7 exon of the eNOS gene in athletes engaged in finswimming and throwing has been studied. The comparative analysis of the obtained data with the frequency of allel variants of the eNOS gene has been carried out in athletes engaged in speed-power sports and the individuals not going in for sports. To study the influence of polymorphisms of this gene on individual values of resistance to hypoxia, a gas analysis was conducted in the athletes practicing rowing. During the study the eNOS gene expression was examined in athletes practicing short-course underwater finswimming with apneapracticing long distance swimming with a snorkel. Results: The findings are evidence of a possible variant of influence of polymorphism of the eNOS gene on the phenotype formation resistant to exercise-induced hypoxia. Conclusions: In the athletes practicing underwater finswimming, the occurrence of the allelic variant of С/С Т→С promoter polymorphism and Т/Т-variant in exon 7 of the gene of NO-synthase is lower than in the general population of Ukraine and in the athletes of speed and power type of sports, which may be the result of selection and be important for peculiarities of the development of resistance to exercise-induced hypoxia with different types of muscle activity. Word count: 2217 Tables: 3 Figures: 2 References: 10 Received: May 2009 Accepted: June 2009 Published: September 2009 Address for correspondence: Svitlana B. Drozdovska, Ph.D. National University Of Physical Education and Sports of Ukraine, Chair of Clinical and Theoretical Human Morphology Fizkultury Str. 1, 03680 Kyiv, Phone: +38(044) 287-54-52, e-mail: SDrozdovska@gmail.com S.B. Drozdovska et al., Allelic Polymorphism of Endothelial No-Synthase (eNOS) Association with Exercise-Induced Hypoxia Adaptation 14 Background It is well-known that nitric oxide (NO) takes part in the processes of the organism adaptation to different types of hypoxia [1]. Its concentration in plasma and erythrocytes increases in the case of hypoxic and circulatory hypoxia [2]. NO concentration in blood depends on the activity of the enzyme of NO-synthase. Gene polymorphism of this enzyme may influence the gene expression and, as a consequence, individual capabilities of triggering the mechanisms of hypoxia compensation [3]. The eNOS gene is located on chromosome 7q35-36 and comprises 26 exons. Among 15 allelic variants of this gene three variants of polymorphism are the most influential. These are the transversion of Т→С in the gene eNOS promoter, the transversion of G→T in exon 7, resulting in the substitution of glutamine to asparagine at position 298 in the eNOS protein, and a variable nucleotide number of tandem repeats in intron 4 (4a/b). By now, only the effect of the intron 4 а/b and G894T polymorphisms of the gene eNOS on the muscle activity and high-altitude adaptation success have been studied [4]. According to the data of Ukrainian researchers, the polymorphism in intron 4 does not considerably affect both the intensity of the eNOS gene expression or the activity of this protein, which explains its insignificant influence on the development of cardiovascular diseases [5, 6]. The allelic polymorphism in exon 7 (G→T) of the gene eNOS contributes greatly to the development of essential arterial hypertension in children and teenagers. The Т/Т variant of this polymorphism is observed 3 times more frequently in patients than in healthy subjects. But the greatest influence on the eNOS gene expression is exerted by the allelic promoter polymorphism of this gene [6, 7]. The presence of the C allele at position 786 of the promoter results in a decrease in its activity, while a lack of eNOS, which takes place in this case, is a reason for the synthesis reduction and a release of nitric oxide and endothelium dysfunction. The intensity of the gene expression of the endothelial NO-synthase is 35% lower in the case of the С/С promoter genotype than in the case of the Т/Т variant, and the activity of NO production by platelets in the subjects with the С/С promoter variant is 2,1 times lower than with the Т/Т genotype. Besides, the fact of the increase in expression of the eNOS gene caused by musle activity is considered as proven [8, 9, 10]. Thus, the aim of our study is to define the possibility of usage of the gene eNOS polymorphisms as molecular-genetic markers of athletes’ resistance to exercise-induced hypoxia. The researchers have set the following tasks: • to study the occurrence of the gene eNOS polymorphous variants in sportsmen adapted to exercise-induced hypoxia. • to examine the regularities of changes of this gene expression with different variants of the gene and adaptation to different physical exercises. Material and Methods During the study 127 highly qualified athletes were examined (30 persons are underwater finswimmers, 41 – rowers, and 56 – sportsmen who practice speed and power track and field exercises (track and field jumps, sprints, throwings). In all these sports types, oxygen deprivation (exercise-induced hypoxia) is observed in the muscular tissue with the intensification of the function of the neuromuscular system. However, the manifestations of hypoxia are different. In speed and power track and field exercises S.B. Drozdovska et al., Allelic Polymorphism of Endothelial No-Synthase (eNOS) Association with Exercise-Induced Hypoxia Adaptation 15 the mechanism of hypoxia development is connected with complete absence of О2. In underwater finswimming the character of exercise-induced hypoxia development is different: for a period of time there is a use of oxygen supply connected with myoglobin and haemoglobin as well as with oxygen, present in residual lung volumes. In rowing exercise-induced hypoxia development is predetermined by the cardio-respiratory system capabilities. The control group included 147 subjects, not engaged in sports. DNA was isolated from the buccal epithelium. Using the method of polymerase chain reaction (PCR) with the following analysis of the length of restriction fragments, the Т→С polymorphism of the promoter and the G→T polymorphism of exon 7 of the еNOS gene were determined. RNA was isolated from the venous blood platelets The eNOS gene expression was determined using the method of real time polymerase chain reaction (Fast 7500 Real Time PCR System (Applied biosystems, USA)). The adaptation to exercise-induced hypoxia was assessed using the gas analysis, where findings were received by means of an automatic gas analyzer of the “Oxycon Pro” type (Jeager, Germany). Loading tests were conducted using the ergometer Concept 2 INDOOR POWER. Results and Discussion The analysis of occurrence of the allelic variants of Т→С promoter polymorphism (Tab.1) has shown that the frequency of normal Т/Т homozygotes among the sportsmen practicing underwater finswimming, adapted to work of mainly anaerobic character of energy supply with hypercapnia development, was 33.5% higher (Р=0.0016) in comparison with a similar frequency in the control group. In the sportsmen specialized in speed and power sports types, it was only 21.2% (Р=0.024) higher than in the control group, and in the sportsmen practicing rowing, it was 6.5% higher. The С/С allelic variant in the group of the sportsmen practicing rowing was observed least often. The minimum frequency of the unfavourable C allele was observed in the group of athletes, practicing underwater finswimming (16.7 % lower than in the control group) (Fig. 1). Tab. 1. Distribution of the allelic variants of Т -786 →С promoter polymorphism of the endothelial NO-synthase in the sportsmen engaged in different types of sports (%) Genotype Underwater finswimming (n=30) Athletes of speed and power kinds of sports (n=56) Rowing (n=41) Control group (n=147) T/T, n (%) 22 (73) 34 (60.7) 19 (46) 58 (39.5) T/C, n (%) 5 (17) 19 (33.9) 20 (49) 75 (51.0) C/C, n (%) 3 (10) 3 (5.4) 2 (5) 14 (9.5) Frequency of С allele, % 18.3 22.3 29.3 35 S.B. Drozdovska et al., Allelic Polymorphism of Endothelial No-Synthase (eNOS) Association with Exercise-Induced Hypoxia Adaptation 16 18.3 22.3 29.3 35 0 5 10 15 20 25 30 35 40