Physiologia, Volume 5, Issue 4 (December 2025) – 8 articles

Recent enthusiasm has surrounded the homeostatic roles that polyamines have in a variety of cell types. Thus, the purpose of this exploratory in vitro study was to determine how spermidine (SPD), a polyamine commonly consumed as a nutritional supplement, affected general markers of cellular health and function in human primary epidermal keratinocytes. Commercial HEKa cells were seeded onto either six-well (transcriptomics and immunoblotting) or 96-well culture plates (viability, ATP, and JC-1 assays) and cultured to ~90+% confluency through complete growth media (CGM) changes every 48 h. Once cells reached this level of growth, treatments included either CGM + phosphate-buffered saline (PBS control, or CTL), CGM + 1 µM SPD, and CGM + 10 µM SPD for either 6 or 24 h depending upon the outcome being assessed. Cellular ATP levels were not significantly affected by 1 µM or 10 µM SPD treatments lasting 24 h. However, cell counts were 9% greater (p = 0.007) when comparing 24 h 10 µM versus CTL treatments indicating increased cell viability. Transcriptomic analyses indicated that 6 h treatments with 10 µM SPD significantly altered 162 transcripts versus non-treated CTL cells (65 up-regulated and 97 down-regulated, p < 0.01). Four pathways were predicted to be enriched based on differential gene expression including protein deubiquitination (GO:0016579), membrane lipid biosynthesis (GO:0046467), DNA metabolic process (GO:0006259), and cell cycle process (GO:0022402). Additionally, the HR gene (essential for keratinocyte hair follicle formation) was significantly up-regulated at the mRNA level with 6 h 10 µM SPD, and immunoblotting confirmed a 96% increase in protein levels with 24 h 10 µM SPD treatments, albeit this did not reach statistical significance (p = 0.102). Pan-keratin protein content was also 60% greater in the 1 µM and 10 µM 24 h treatments than CTL (p ≤ 0.029). Finally, although select markers of mitochondrial content and biogenesis were not significantly altered with 6 h and 24 h treatments, mitochondrial membrane potential (an aspect of mitochondrial function) was 84% greater with 24 h 1 µM versus CTL (p < 0.001). In conclusion, these preliminary screening experiments in unperturbed human keratinocytes suggest that exogenous SPD positively affects various aspects of homeostasis by stimulating transcriptomic and functional alterations (e.g., increased cell viability and enhanced keratinocyte protein levels). Full article

Background/Objectives: This study aimed to objectively assess fatigue levels using facial expressions. Methods: This study included 25 female nurses aged between 30 and 50 years. We compared their subjective and objective fatigue levels after a night shift, when accumulated fatigue was assumed, with those after a day off, when recovery was expected. Fatigue levels were subjectively assessed using questionnaires and were also quantified by the Visual Analog Scale (VAS). Objective evaluations included (1) the degree of eye-opening, (2) the maximum distance and speed of facial skin movement by tracking changes in coordinate values of facial markers on the skin during intentional smiling, and (3) analysis of high-frequency (HF) components and the low frequency-to-high frequency (LF/HF) ratio in heart rate variability (HRV). Results: After a night shift, compared to after a day off, subjective assessments of mental and physical fatigue in the questionnaires and VAS values of own fatigue were significantly elevated. Concurrently, objective evaluations revealed that the degree of eye-opening, along with the maximum movement distance and speed of the lower eyelid, cheek, and mouth corners during intentional smiling, were significantly reduced. Furthermore, the HF component, an index of parasympathetic activity, significantly decreased, whereas the LF/HF ratio, an index of sympathetic activity, significantly increased. Additionally, significant correlations were observed between subjective VAS estimation of fatigue levels and each objective parameter examined. Conclusions: Measuring facial parameters is an effective method for objectively assessing facial expressions of fatigue, and these changes are mediated through reduced parasympathetic nervous activity and increased sympathetic nervous activity during fatigue. Full article

Background: The study of psychophysiological responses to disgust-evoking stimuli has long been neglected in favour of other emotional stimuli, especially those evoking fear. While the basic cascade of responses to a frightening stimulus is relatively well-understood, psychophysiological responses to disgust-related threats, such as parasites or rotten food, are scarcely studied. Methods: Here, we aimed to assess skin resistance (SR) change as a measure of electrodermal response to visual cues that signal the presence of disgust-relevant threats. To this aim, we recruited 123 participants and presented them with one of the following varieties of disgust-relevant threats: disgust-evoking animals (e.g., parasites, worms), spoiled food, threat of pandemic, or pollution and toxicity. The latter two represented modern threats to test whether also these modern stimuli can initiate immediate automatic reaction. Results: We found significant differences between the categories: Participants responded with the highest probability to disgust-evoking animals (38%) and sneezing (52%), suggesting that only ancestral cues of pathogen disgust trigger automatic physiological response. Moreover, we found significant inter-sexual differences: women exhibited more SR change responses than men, and the amplitude of these responses was overall larger. Finally, we report a weak effect of subjectively perceived disgust intensity on reactivity to threat stimuli. Conclusions: We discuss heterogeneity of disgust-relevant threats, their adequate behavioural responses, and subsequent heterogeneity of respective SR responses. We conclude that large interindividual variability might eclipse systematic differences between participants with high or low sensitivity to disgust, and that subjectively perceived intensity of disgust is only a weak predictor of electrodermal response to its elicitor. Full article

Aims: The present study evaluated the acute morning effect of melatonin supplementation (5 mg) on cardiometabolic responses. Methods: For this purpose, 12 physically active men (22.1 ± 1.3 years; 1.7 ± 01 m; 74.7 ± 12.1 kg; 24.3 ± 2.7 m/kg²; VO₂max: 46.9 ± 2.3 mL/kg/min; 17.3 ± 5.2%F) were measured in a double-blind crossover protocol, where participants were measured before, during, and after a high-intensity interval exercise (HIIE) protocol [4 × 4 min at 95% of maximum heart rate (HRmax) with a 3 min interval at 60–70% of HRmax] followed by 30 min of recovery. At rest, the following variables were measured: HR, systolic blood pressure (SBP), diastolic blood pressure (DBP), lactate, and maximum oxygen consumption (VO₂max). At the end of each stage and interval, VO₂, respiratory exchange ratio (RER), and HR were measured. During recovery, VO₂, VCO₂, RER, SBP, DBP, and HR were measured. Results: Melatonin significantly enhanced recovery metabolism, as evidenced by increased VO₂ at Interval 3 (+2.2 mL/kg/min, p = 0.03, d = 0.69) and 5 min postexercise (+2.4 mL/kg/min, p = 0.02, d = 0.81). The RER was higher during Sprint 4 (+0.08, p = 0.01, d = 0.84), indicating greater carbohydrate reliance. Cardiovascular recovery was also improved, with a reduced HR at 30 min (−5 bpm, p = 0.04, d = 0.66) and lower SBP at 15 min (−8 mmHg, p = 0.02, d = 0.75). Lactate concentration at 30 min was lower with melatonin (−0.7 mmol/L, p = 0.03, d = 0.72). No significant effects were observed at rest or during early exercise. Conclusions: Acute morning melatonin intake may amplify metabolic responses to HIIE while facilitating cardiometabolic recovery. This dual-phase action may benefit athletes aiming to optimize energy expenditure, fat metabolism, and recovery during early-day training. Full article

Background: The high-intensity demands of CrossFit induce respiratory muscle fatigue, potentially impairing performance via the metaboreflex. Respiratory muscle training (RMT) may mitigate this effect, but evidence in female athletes remains limited. Objective: We aimed to investigate the effects of RMT on sport-specific performance and maximal inspiratory pressure (PIMAX) in recreational female CrossFit practitioners. Design: We conducted a parallel-group randomized controlled trial. Setting: The study was conducted in a CrossFit-affiliated gym. Participants: We recruited twenty-nine recreational female practitioners (age: 30.3 ± 7.9 years) with ≥1 year of uninterrupted training who were free from respiratory diseases. Interventions: Participants were randomized to a CrossFit-only group (n = 14) or CrossFit + RMT group (n = 15). Both trained 5 days/week for 6 weeks; the RMT group additionally performed 30 inspiratory efforts at 50% of PIMAX, 5 days/week, with weekly load adjustment. Main Outcome Measures: Primary: Sport-specific performance (total repetitions in a 10-min AMRAP [As Many Rounds As Possible] test). Secondary: PIMAX (cmH₂O). Measurements were taken pre- and post-intervention. Results: Baseline performance and PIMAX were similar between groups. After 6 weeks, the CrossFit + RMT group improved in performance more (Δ = +10.5 ± 10.7 reps, p = 0.03, ηp² = 0.168) than the CrossFit-only group (Δ = +2.3 ± 8.1). PIMAX gains were also greater with RMT (Δ = +19.6 ± 8.4 cmH₂O, p = 0.043, ηp² = 0.148) vs. control (Δ = +10.1 ± 9.7). No adverse events occurred. Conclusions: Adding RMT to CrossFit training enhanced sport-specific performance and inspiratory strength in recreational female practitioners more than CrossFit alone. RMT appears to be a safe and effective complementary strategy for high-intensity functional training. Full article

Background: Rowing is a highly demanding endurance sport, requiring simultaneous work of approximately 70% of the body’s muscle mass and the combined contribution of aerobic and anaerobic energy systems. Objective: This study aimed to analyze the cardiorespiratory responses and performance characteristics of elite junior male and female rowers during maximal effort over 2000 m on a rowing ergometer. Methods: Fifteen junior rowers (six males aged 15–17 and nine females aged 15–18) participated in the study. Anthropometric data (body height, weight, and body surface area) were recorded. All participants performed a maximal 2000 m test on a Concept2 D-model ergometer. Throughout the test, oxygen uptake (VO₂), carbon dioxide production (VCO₂), heart rate, and ventilation parameters were continuously measured. Performance and physiological data were analyzed in three intensity zones, defined by ventilatory thresholds (VT1–VT3), as well as at peak exercise. Results: Significant anthropometric differences were observed between genders. In terms of performance, males completed the 2000 m test significantly faster than females (208.83 ± 87.66 s vs. 333.78 ± 97.51 s, p = 0.0253). Relative VO₂ at peak exercise was higher in males (58.73 ± 5.25 mL·kg⁻¹·min⁻¹) than females (48.32 ± 6.09 mL·kg⁻¹·min⁻¹, p = 0.0046). In most cardiorespiratory parameters, males outperformed females significantly, except for heart rate and ventilatory equivalents. Ranking analysis revealed that higher VO₂max values were generally associated with a better placement in both genders, though this relationship was not perfectly linear. Performance time was negatively correlated with VO₂Peak (r = −0.8286; p < 0.001), rVO₂Peak (r = −0.6781; p < 0.01), and O₂P_Peak (r = −0.7729; p < 0.01). Conclusions: The findings confirm significant gender differences in anthropometric and cardiorespiratory characteristics of elite junior rowers and reinforce VO₂max as a key determinant of performance. Yet, deviations from a direct VO₂max–rank correlation highlight the influence of tactical, psychological, and biomechanical factors. Future research should provide practical recommendations for monitoring performance and tailoring training to optimize adaptation and long-term athlete development. Full article

Serotonin (5-hydroxytryptamine—5-HT) is an important neurotransmitter that exerts a remarkably large array of biological roles in the central nervous system and at the body level. It is involved in generating emotions, being a natural mood stabilizer; it reduces depression, anxiety, modulates sleep, and has many other effects. It is also involved in fetal and postnatal brain development. This variety of biological effects, particularly in the central nervous system, with influence on behavior and cognitive functions, relies on a large number of pre- and postsynaptic serotonin receptor (5-HTR) isoforms spread throughout the brain. They can be grouped in seven large families and include over 18 subtypes, identified based on gene sequences, expression patterns, and pharmacological responses. While in vertebrates these receptors have been properly characterized and described, their correspondents in invertebrates have been far less explored, despite the assumption that they may have similar properties to those described in vertebrates. This paper summarizes the current knowledge in several important areas that together define the entire scope of serotonin receptor research, with a particular emphasis on the role of serotonergic central pathways and circuitry in thermoregulation and correlations with neurologic and psychiatric pathology. Full article

Intracellular oxidation–reduction (redox) potential is a key factor regulating various physiological phenomena in the cell. Monitoring this potential change is therefore important for understanding physiological homeostasis in cells. Herein, we propose a new approach for the real-time, non-invasive estimation of the redox potential impacting biological metabolism and reactive oxygen species generation. Enzymes, specifically oxidoreductases, play a crucial role in catalyzing redox reactions by facilitating the transfer of electrons and hydrogen atoms between molecules. The redox potential of substrates, such as nicotinamide adenine dinucleotide, is determined by the ratio of its oxidized and reduced forms, while that of enzymes, such as succinate dehydrogenase, is determined using the reference electrode in protein-film voltammetry. Although the standard hydrogen electrode potential is defined as zero under standard conditions, the electrode potential of a reversible hydrogen electrode changes according to the ratio of the hydrogen ions (H⁺) and hydrogen gas (H₂) in the biological fluids, as a reference electrode. The pH is maintained at 7.4 ± 0.1 in the arterial blood and the H₂ that produced by the gut microbiota is measured in the endo-tidal breath for clinical diagnosis. The H₂ in the endo-tidal breath equilibrates arterial blood during gas exchange in the lungs, as well as in whole-body tissues, due to the systemic circulation. In this study, H₂ can be measured in the environmental gas compared to the atmosphere, and may serve as a novel factor for redox potential changes in redox enzymes, impacting biological metabolism and reactive oxygen species generation. Full article