Background: Physiological rhythms in mammals are essential for maintaining health, whereas disruptions may cause or exacerbate disease pathogenesis. As such, our objective was to characterize how cigarette smoke exposure affects physiological rhythms of otherwise healthy mice using telemetry and cosinor analysis. Methods: Female BALB/c mice were implanted with telemetry devices to measure body temperature, heart rate, systolic blood pressure (SBP), and activity. Following baseline measurements, mice were exposed to cigarette smoke for approximately 50 min twice daily during weekdays over 24 weeks. Physiological parameters were recorded after 1, 4, 8, and 24 weeks of exposure or after 4 weeks cessation following 4 weeks of cigarette smoke exposure. Results: Acute cigarette smoke exposure resulted in anapyrexia, and bradycardia, with divergent effects on SBP. Long term, cigarette smoke exposure disrupted physiological rhythms after just 1 week, which persisted across 24 weeks of exposure (as shown by mixed effects on mesor, amplitude, acrophase, and goodness-of-fit using cosinor analysis). Four weeks of cessation was insufficient to allow full recovery of rhythms. Conclusion: Our characterization of the pathophysiology of cigarette smoke exposure on physiological rhythms of mice suggests that rhythm disruption may precede and contribute to disease pathogenesis. These findings provide a clear rationale and guide for the future use of chronotherapeutics.

Purpose: To use repeated control trials to measure within-subject variability and assess the existence of responders to ischemic preconditioning (IPC). Secondly, to determine whether repeated IPC can evoke a dosed ergogenic response. Methods: Twelve aerobically fit individuals each completed three control and three IPC 5-km cycling time trials. IPC trials included: (i) IPC 15-min preceding the trial (traditional IPC), (ii) IPC 24-h and 15-min preceding (IPC × 2), (iii) IPC 48h, 24-h, and 15-min preceding (IPC × 3). IPC consisted of 3 × 5-min cycles of occlusion and reperfusion at the upper thighs. To assess the existence of a true response to IPC, individual performance following traditional IPC was compared to each individual's own 5-km TT coefficient of variation. In individuals who responded to IPC, all three IPC conditions were compared to the mean of the three control trials (CON avg ) to determine whether repeated IPC can evoke a dosed ergogenic response. Results: 9 of 12 (75%) participants improved 5-km time (−1.8 ± 1.7%) following traditional IPC, however, only 7 of 12 (58%) improved greater than their own variability between repeated controls (true responders). In true responders only, we observed a significant mean improvement in 5-km TT completion following traditional IPC (478 ± 50 s), IPC × 2 (481 ± 51 s), and IPC × 3 (480.5 ± 49 s) compared to mean CON avg (488 ± 51s; p < 0.006), with no differences between various IPC trials (p > 0.05). Conclusion: A majority of participants responded to IPC, providing support for a meaningful IPC-mediated performance benefit. However, repeated bouts of IPC on consecutive days do not enhance the ergogenic effect of a single bout of IPC.

Techniques to comprehensively evaluate pulmonary function carry a variety of limitations, including the ability to continuously record intrathoracic pressures (ITP), acutely and chronically, in a natural state of freely behaving animals. Measurement of ITP can be used to derive other respiratory parameters, which provide insight to lung health. Our aim was to develop a surgical approach for the placement of a telemetry pressure sensor to measure ITP, providing the ability to chronically measure peak pressure, breath frequency, and timing of the respiratory cycle to facilitate circadian analyses related to breathing patterns. Applications of this technique are shown using a moderate hypoxic challenge. Male C57Bl6 mice were implanted with radio-telemetry devices to record heart rate, temperature, activity, and ITP during 24 h normoxia, 24 h hypoxia (FIO2 = 0.15), and return to 48 h normoxia. Radio-telemetry of ITP permitted the detection of hypoxia-induced increases in 'the ITP-equivalent' of ventilation, which were driven by increases in breathing frequency and ITP on a short-term timescale. Respiratory frequency, derived from pressure waveforms, was increased by a decrease in expiratory time without changes in inspiratory time. Chronically, telemetric recording allowed for circadian analyses of respiratory drive, as assessed by inspiratory pressure divided by inspiratory time, which was increased by hypoxia and remained elevated for 48 h of recovery. Further, respiratory frequency demonstrated a circadian rhythm, which was disrupted through the recovery period. Radio telemetry of ITP is a viable, long-term, chronic methodology that extends traditional methods to evaluate respiratory function in mice.

Background In response to hypoxia, the kidney is considered the major source for erythropoietin (EPO) – a protein responsible for stimulating hematopoiesis. Interestingly, recombinant human EPO (rhEPO) also has known anti‐apoptotic, cardioprotective, and inotropic effects. Preclinically, supraphysiological concentrations of rhEPO, given at the time of permanent coronary artery occlusion, is effective at reducing apoptosis in the area‐at‐risk, infarct size, and left ventricular remodeling and functional deficits. Clinically, researchers have encountered significant translational difficulties using EPO post‐myocardial infarction, as the hematopoietic effect of chronic rhEPO dosing limits its therapeutic use in patients. Emerging findings demonstrate that EPO mRNA expression occurs in non‐renal tissues, including the liver, bone, and reproductive organs, yet the evidence is divided with regards to the heart. Our preliminary data shows that cardiac EPO expression is upregulated during embryonic development, suggesting it has a paracrine role in cardiac development. Therefore, whether the adult heart produces EPO under a stress (e.g., myocardial infarction) and has physiological relevance remains unknown. Notably, in humans, serum EPO levels are elevated at 3 days post‐myocardial infarction, which indicates that the injured/hypoxic heart may produce EPO in vivo. Accordingly, our objective was to improve our understanding of the regulation and physiological significance of cardiac‐derived EPO using a murine model of myocardial infarction. It was hypothesized that a myocardial infarction would increase cardiac EPO mRNA expression, which may serve as a paracrine factor to preserve cardiac structure and function following an ischemic injury. Methods and Results Male CD1 mice were subjected to permanent ligation of the left anterior descending coronary artery to induce a myocardial infarction. At 12 h post‐surgery, hearts were harvested for qPCR analyses, which showed a significant upregulation in EPO mRNA expression. At 2, 4, and 9 weeks post‐myocardial infarction (when hearts were anoxic), hematocrit was significantly elevated, compared to age‐matched shams, indicating that serum EPO levels were still increased at these timepoints. To investigate whether cardiac EPO is driven solely by hypoxia, we subjected mice to severe hypoxia (9% O2) for 24 h and evaluated EPO mRNA expression in the heart and kidney. Indeed, EPO expression was significantly increased in the kidney, while we observed a very modest increase in the heart. Conclusions Here we show that the heart is a significant non‐renal source of EPO post‐myocardial infarction. Further, profound hypoxia does not significantly drive cardiac‐derived EPO expression, suggesting it is regulated by a hypoxia‐independent mechanism post‐injury. Taken together, endogenous cardiac EPO production may be elevated to provide paracrine cardioprotective support following a myocardial infarction. Support or Funding Information Canadian Institutes of Health Research. Natural Sciences...

Introduction Erythropoietin (EPO), in response to hypoxia, is produced by the kidney, which stimulates erythropoiesis in the bone marrow. While the kidney is regarded as the primary source of EPO, mainly in vitro expression has been shown from cells or tissues of the brain, liver, and reproductive organs. However, whether these organs are an endogenous extra‐renal source and their physiological significance is unknown. Interestingly, recombinant human EPO (rhEPO) confers cardiac cytoprotection and increases contractility. Albeit, this occurs using supra‐physiological doses of rhEPO. Whether the kidney is responsible for these effects remains to be elucidated. Therefore, the primary objective of this research is to investigate the physiological relevance of endogenous cardiomyocyte EPO production. We hypothesized that: 1) adult cardiomyoctes are a source of EPO production and 2) the loss of cardiomyocyte EPO expression leads to a decrease in contractility and an increase in susceptibility to ischemia‐reperfusion injury. Methods Cardiomyocyte‐specific deletion of EPO (EPOfl/fl‐CM) was obtained by injecting 8‐week old α‐MHC‐MerCreMer+/−: EPO fl/fl male mice with 20 mg/kg tamoxifen daily for 5 days. Left ventricular (LV) EPO expression was determined using qPCR analysis. Cardiac structure and function were assessed by echocardiography, invasive hemodynamics and the Langendorff, respectively. Hematocrit was measured from blood collected via saphenous vein. Data was obtained 8‐weeks post‐tamoxifen. Results Paradoxically, EPOfl/fl‐CM mice exhibited a dramatic increase in whole heart EPO expression. Further, cardiac‐derived EPO confers inotropic, lusitropic and hypertrophic effects. Furthermore, in response to ischemia‐reperfusion injury, EPOfl/fl‐CM mice show profound cytoprotection. Importantly, we show that endogenous cardiac‐derived EPO is capable of improving cardiac function without affecting whole body Hct levels. Conclusion The knock‐out of EPO from the cardiomyocyte leads to a reciprocal increase in LV EPO expression, whereby an alternate cell in the heart is over‐compensating for the loss of cardiomyocyte‐derived EPO. This study furthers our fundamental understanding of EPO biology and establishes it as a novel cardiac myokine, capable of increasing cardiac function and driving hypertrophy. Support or Funding Information Heart and Stroke FoundationCanadian Institutes of Health Research