The Influence of Exercise on the Daily Rhythm of Serum Homocysteine in Horses

Abstract

Abstract:The aim of this study was to determine the daily rhythms in the blood serum of homocysteine in horses. Ten thoroughbred horses, five athletic (trained for 1 h, 6 days a week) and five sedentary, were used. Blood samples were collected on each subject every 4 h for two days by means of the jugular vein. On each individual sample, the serum concentration of homocysteine was assessed. The results obtained during the experimental period indicated the existence of a daily rhythm of serum homocysteine in sedentary and athletic horses. They also demonstrated that in horses, physical exercise influences the daily rhythm of serum homocysteine.Key words: circadian rhythms, homocysteine, horse.Homocysteine (Hcy) is a sulfur intermediate amino acid in methionine-cysteine metabolism [1]. The importance of this metabolic pathway relates to the sheer number of physiological functions in which it is involved; it contains the methyl donor (S-adenosyl-methionine) for virtually all methylation reactions in the organism [2] and provides the limiting substrate (cysteine) for the synthesis of glutathione [3]. The metabolism of Hcy leads to three possible main outcomes: it may be remethylated to methionine, converted to cysteine by transulfuration, or exported to the extracellular space. In man, moderately increased concentrations of total homocysteine (tHcy) have been identified as an independent risk factor for cardiovascular disease (CVD), stroke, and other thrombotic events [4][5][6][7][8][9][10][11], as well as increased concentrations of total cysteine (tCys) [12]. Regular physical exercise is now recognized to reduce the risk of CVD development [13,14]. Sedentary subjects, however, are considered to be at risk for CVD. Although available evidence indicates that physical activity modifies the lipid and carbohydrate metabolism [15], non energetic exercise-induced metabolism stress has not been extensively studied [16]. Recent data have pointed out that the duration and intensity of exercise are relevant factors in modulating the plasma Hcy levels. Bailey et al. [17] have shown that a 4-week exercise program was associated with a reduction in Hcy levels in healthy men, whereas Nygard et al. [18] confirmed that a lack of exercise might be partly associated with elevated plasma tHcy levels, increasing the risk of CVD in the elderly. As far as horses are concerned, there are not many studies on homocysteine, neither on the effects derived from training nor on its daily rhythm. The few that are available deal with the physiological range of Hcy and its variations in relation to some pathologies [19] and the influence of a single exercise test, but not training, on the plasmatic levels of homocysteine [20]. As for studies on daily rhythm in men [21][22][23] and rats [24,25], it is evident that the rhythmicity of the parameter and the influence of physical exercise have been considered only together, never separately. It is known that many circadian rhythms in physiological functions are evident under resting conditions and tha...

Daily pattern of some fatty acids in the athletic horse

“…Physical exercise, regularly undertaken in the early afternoon, might be the exogenous zeitgebers that trigger the daily rhythm of these parameters. Furthermore, the effects of exercise, training in particular, on several physiological–metabolic parameters in men (Reilly et al., 1997) and horses (Piccione et al., 2005a,b; Fazio et al., 2006) are well known. For example, we showed in our previous research the existence of the circadian rhythm of tryptophan and serotonin in sedentary and athletic horses.…”

“…For example, we showed in our previous research the existence of the circadian rhythm of tryptophan and serotonin in sedentary and athletic horses. It is interesting that both parameters changed their acrophases in athletic horses trained in the afternoon (Piccione et al., 2005a; Fazio et al., 2006). The detection of the factors able to determine and influence the periodicity of the energetic parameters is of fundamental importance to establish a chronogram or reference for the objective assessment of the sport performance and the planning of training programmes.…”

State of the art on daily rhythms of physiology and behaviour in horses

“…For example, the afternoon physical exercise of horses might determine the shift of the homocysteine acrophase from diurnal to nocturnal (Fazio et al 2006). Also non-esterified fatty acids (NEFA), palmitic, stearic, oleic, linoleic and linolenic acids' circadian rhythms are influenced by physical exercise (Piccione et al 2009b).…”

Daily rhythm of tear production in normal horse

“…Studies in humans and dogs described a diurnal variation in tear turnover rate 5,6 . In the study of other physiological parameters, the pattern of diurnal variation was found to be affected by a number of endogenous and exogenous factors such as age, 7,8 season, 9–11 feeding times and fasting, 12–14 isolation, 15 exercise, 16,17 electro‐magnetic field, 18,19 change in light intensity and environmental temperature 10 . Normal STT has recently been shown to be affected by age, gender, time of day, season, environmental condition and placement of strips 20,21 .…”