Ultradian and Infradian Rhythms in the Dynamic of Testosterone Concentration in the Serum of the White-Breasted Hedgehog Erinaceus roumanicus

Abstract

the aim of the study was to identify ultradian (intraday) and infradian (multi-day) rhythms in the dynamics of testosterone concentration in the blood serum of white-breasted hedgehogs. Blood sampling was performed from the femoral veins of 12 male hedgehogs. We found ultradian rhythms of testosterone on both sampling dates-March 7-8 (a day length of 11 hours and 15 minutes) and May 10-11 (a day length of 16 hours). An 8-hour rhythm of testosterone concentration has been established. the acrophases were at the same times in both photoperiods and thus independent of sunset times. The study of the infradian rhythms of testosterone was daily carried out on May 22-June 3, at 07:40 to 08:50 and from June 27 to July 7, at 16:15-16:50. It revealed an infradian rhythm of the testosterone concentration with a period of 4-days in both the morning and the evening sampling. According to our previous investigation, the infradian rhythms of testosterone among individual hedgehogs, rodents and primates have the same period. that indicates the common mechanisms for their formation. in case of experimental studies, the phase of ultradian and infradian biorhythms will need to be taken into account because the testosterone concentration in acrophase is 2-4 times higher than in bathyphase. The dynamics of physiological indicators of the organism have not only circadian but also ultradian and infradian rhythms 1-4. Unlike circadian biorhythms, the mechanisms of ultradian and infradian biorhythms formation is not yet understood. However, there are facts pointing to the relationship of these biorhythms with quasi-rhythmic fluctuations of environmental factors, which differ from light/dark mode 5,6. Recently 2-6 hourly fluctuations of various physiological indicators, in particular, motor activity, sleep, nutrition, body temperature and serum hormone levels have been studied 7-9. It was shown that the activity of the hypothalamic-pituitary-adrenal axis has both circadian and ultradian rhythms 9. Ultradian glucocorticoid hormone secretion rhythms are important for normal gene transcription, regulation of metabolism, inflammation, (cognition, memory) and reactions to stress. However, the nervous and endocrine processes that determine these rhythms are not fully understood 9. It was shown that the identified dopaminergic oscillator has a period of about 4 hours and, along with the circadian oscillator, controls the rest/activity cycle. Furthermore, the disruption of the dopamine transporter gene leads to an increase in the period of locomotor ultradian rhythms in mice, and the striatal dopamine levels fluctuate in synchrony with the ultradian activity cycles 10. It is well-known that there are circaseptan (about-weekly) and circasemiseptan (about-half-weekly) infradian biorhythms of the glucocorticoid hormones concentration, melatonin level, mitotic activity, sodium excretion, heart rate variability, etc. 11-15. It is assumed that these rhythms, as well as circadian, are self-sustaining and have external synchronisers that have not yet bee...

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