Infradian 4-Day Rhythm of Proliferative Activity of L-929 Mouse Fibroblast Culture in the Logarithmic Growth Phase Is Exogenous.

We studied the dynamic of proliferative activity of cultured mouse transformed fibroblast-like L-929 cells in the logarithmic growth phase. During a long period (December 5-23, 2020), we revealed a 4-day rhythm of daily increase in the number of L-929 cells with an amplitude not lower than in a culture of embryonic fibroblast-like cells. Hence, the formation of the 4-day rhythm is not associated with the molecular mechanisms of inhibition of proliferation, which are absent in transformed cells. Daily thawing of samples of one culture over 17 days showed the presence of a 4-day rhythm synchronous between all thawed samples and the control cell culture. As deep freezing leads to the cessation of all life processes in cells, the formation of a 4-day rhythm of proliferative activity of cell culture is determined by an exogenous mechanism.

Infradian Modulation of Circadian Rhythm in Small Mammals and Birds under Constant Light.

The study examined the infradian rhythms in total motor activity and the periods of "freerunning" circadian rhythm in male C57BL/6 mice and European greenfinch Chloris chloris exposed to constant light. In birds and mice, the motor activity was characterized with inphase 4-day-long rhythm. The periods of free-running circadian rhythms in birds and mice were 23 and 25 h, respectively, and they were modulated with 4-day-long periodicity. The maximal deviations in the period of free-running circadian rhythm from the individual mean levels coincided with the acrophase of 4-day-long rhythm of motor activity in both species.

Infradian Rhythm in Proliferative Activity of a Culture of Embryonic Fibroblast-Like Cells from C57BL/6 Mice.

We studied daily dynamics of proliferative activity of embryonic fibroblast-like cells in culture during the logarithmic growth phase. Daily increase in cell count in the culture showed a 4-day rhythm that persisted over 3 weeks of culturing. In cultures from different animals, the phase of this rhythm was synchronous and did not depend on the moment of cell isolation. It can be hypothesized that the 4-day biorhythm of proliferative activity of embryonic fibroblast-like cells in culture is determined by external environmental factors, probably of electromagnetic nature.

Sodium Handling and Interaction in Numerous Organs.

Salt (NaCl) is a prerequisite for life. Excessive intake of salt, however, is said to increase disease risk, including hypertension, arteriosclerosis, heart failure, renal disease, stroke, and cancer. Therefore, considerable research has been expended on the mechanism of sodium handling based on the current concepts of sodium balance. The studies have necessarily relied on relatively short-term experiments and focused on extremes of salt intake in humans. Ultra-long-term salt balance has received far less attention. We performed long-term salt balance studies at intakes of 6, 9, and 12 g/day and found that although the kidney remains the long-term excretory gate, tissue and plasma sodium concentrations are not necessarily the same and that urinary salt excretion does not necessarily reflect total-body salt content. We found that to excrete salt, the body makes a great effort to conserve water, resulting in a natriuretic-ureotelic principle of salt excretion. Of note, renal sodium handling is characterized by osmolyte excretion with anti-parallel water reabsorption, a state-of-affairs that is achieved through the interaction of multiple organs. In this review, we discuss novel sodium and water balance concepts in reference to our ultra-long-term study. An important key to understanding body sodium metabolism is to focus on water conservation, a biological principle to protect from dehydration, since excess dietary salt excretion into the urine predisposes to renal water loss because of natriuresis. We believe that our research direction is relevant not only to salt balance but also to cardiovascular regulatory mechanisms.

Infradian and Ultradian Rhythms of Body Temperature Resumption during Hibernation.

The rhythms of short-term arousal episodes, associated with normalization of low body temperature, were studied in hibernating Erinaceus roumanicus. The episodes of body temperature recovery during hibernation were 1.7 times more incident during the acrophase of 4.058-day rhythm of glucocorticoid hormones, detected previously, than during the batiphase of this rhythm. Ultradian rhythm of arousal episodes conformed to a 4-h biorhythm: the maximum number of body temperature resumption episodes was recorded at 00.00-01.00, 04.00-05.00, 08.00-09.00, 12.00-13.00, 16.00-17.00, and 20.00-21.00. These data indicated that in mammals the mechanisms of infradian and ultradian rhythm maintenance were stable and did not depend on body temperature or were determined by external factors with periods of 4.058 days and 4 h.

Sperm physiology varies according to ultradian and infradian rhythms.

The spermatozoon must be physiologically prepared to fertilize the egg, process called capacitation. Human sperm samples are heterogeneous in their ability to capacitate themselves, which leads to variability between samples from the same or different donors, and even along the seasons. Here we studied sperm variation in the capacitation state according to the ability of capacitated spermatozoa to acrosome react upon stimulation (% ARi) and to be recruited by chemotaxis (% Chex). Both indirect indicators of sperm capacitation increased along the incubation time with fluctuations. Those capacitated sperm recruited by chemotaxis showed an ultradian rhythm with a cycle every 2 h, which might be influenced by unknown intrinsic sperm factors. Two infradian rhythms of 12 months for the % ARi and of 6 months for % Chex were observed, which are associated with the joint action of temperature and photoperiod. Thus, to avoid false negative results, human sperm samples are recommended to be incubated for a long period (e.g. 18 h) preferably in spring time. This innovative point of view would lead to better comprehend human reproductive biology and to think experimental designs in the light of sperm cyclicity or to improve sperm aptitude for clinical purposes.

Infradian Rhythms of Resistance to a Dissociative Anesthetic in Wistar Male Rats under Normal Conditions and After Surgical Removal of the Adrenal Glands and Testes.

Daily dynamics of changes in the latency of a response to dissociative anesthetic tiletamine (time from injection to ataxia) was studied in mature Wistar rats. Both intramuscular and intravenous administration of the anesthetic was associated with 4-day oscillations of the latent period synchronous with the dynamics of changes in the concentration of glucocorticoid hormones. The period and phases of the infradian rhythm of resistance to the anesthetic remained unchanged after removal of both adrenal glands and testes and administration of corticosterone synthesis blocker trilostane diminishing the 4-day cycle of changes in corticosterone level. Therefore, hormones of the adrenal glands and testes do not play the key role in the mechanisms of formation of the 4-day infradian rhythm.

Microscopic markers of an infradian biorhythm in human juvenile ribs.

Recent studies have indicated that there may be an infradian systemic biorhythm that coordinates aspects of human hard tissue growth and influences adult body size. Here we investigate if evidence of this biorhythm retained in human teeth as the periodicity of Retzius lines (RP) corresponds with the microstructural growth of a non-weight bearing bone, the rib, in a sample of 50 human juvenile skeletons. Using static histomorphometric methods, the RP of one permanent tooth from each skeleton was calculated and combined with measures of bone remodeling in a rib from the same individual. Results provide the first evidence that the infradian biorhythm is linked to bone remodeling in children. Retzius periodicity was negatively correlated with relative osteon area (r = -0.563, p = 0.008) and positively related to Haversian canal area (r = 0.635, p = 0.002) and diameter (r = 0.671, p = 0.001) in children between the age of 8 to 12 years. There was also a negative correlation between RP and the relative cortical area of ribs (r = -0.500, p = 0.048). Relationships between bone remodeling and the biorhythm were much more variable in younger children. Results imply that as the biorhythm speeds up there is increased bone deposition during remodeling of the rib, leading to the larger osteonal lamellar bone areas and smaller Haversian canals in children between 8 and 12 years of age. Our results support the idea that there is an infradian biorhythm that coordinates aspects of human hard tissue growth.

Infradian Rhythm of the Content of Secretory Granules in Pinealocyte Cytoplasm in Mice and Rats.

The numerical density of secretory granules dense-core vesicles (DCV) in the cytoplasm of pinealocytes of the pineal gland was estimated by transmission electron microscopy in male white mice and Wistar rats. The 3-day biorhythm and lunaphase changes in the DCV content in the perikaryon and the processes of pinealocytes, which are manifested significantly in different seasons of the year, are established. The three-day biorhythm in adult male mice in comparison with younger male rats is not expressed uniformly in different phases of the moon. The in-phase manifestation of infradian biorhythms in different species of animals during the year with an unchanged daily photophase indicates the existence of common external synchronizers for mammals of these biorhythms that are not associated with the light/dark cycle.

Relationship between Hypoxic Resistance and the Phase of 4-Day Corticosterone Biorhythm in Adult Male Rats.

The relationship between the phase of 4-day serum corticosteroid biorhythm and resistance to acute hypobaric hypoxia was studied in male rats. Single evaluations of hypoxic resistance of Wistar rats during the same time of the day have shown that the lifespan of animals is significantly longer during the 4-day biorhythm acrophase than during the bathyphase. Daily testing for 12 days has detected a 4-day rhythm of hypoxic resistance, synphasic with corticosterone biorhythm, irrespective of the wave-like course of the adaptation process phase from the beginning of daily testing and hypoxic resistance. Experiments on Sprague-Dawley rats have shown that animals highly resistant and medium resistant to hypoxia during the infradian biorhythm acrophase become medium resistant and poorly resistant during the bathyphase. In order to detect the animals with the least hypoxic resistance in the population, the studies should be carried out during the 4-day infradian biorhythm acrophase, while detection of the most resistant animals should be carried out during the bathyphase.