Cardiovascular function and autonomic regulation in urethane-anesthetized and conscious mice

Urethane is widely used for its ability to induce prolonged anesthesia. Variability in previously reported cardiovascular parameters in murine models makes it challenging to definitively evaluate the cardiovascular effects of urethane anesthesia. We aimed to address these challenges, thereby advancing our understanding of urethane's effects on cardiovascular function in mice. In this study, we investigated how urethane anesthesia, with and without supplemental oxygen, impacts heart rate, arterial oxygen saturation ([Formula: see text]), blood pressure, and heart rate variability in mice. First, we conducted a literature review and found that data in mice were both limited and lacking in reproduction. Next, we conducted a series of physiological measurements to address gaps in the literature and subjected C57BL/6J mice to three conditions: 1) conscious, 2) urethane-anesthetized, and 3) urethane-anesthetized with supplemental oxygen. Blood pressure, heart rate, [Formula: see text], and heart rate variability (via time, frequency, and M-curve analyses) were assessed. We observed an increase in heart rate with urethane anesthesia (P = 0.012) compared with the conscious state. Urethane caused a decrease in heart rate variability, which was independent of oxygen supplementation. Urethane anesthesia caused a significant reduction in arterial blood pressure (P < 0.001) with oxygen-supplemented mice remained hypotensive. Urethane decreased [Formula: see text] (P = 0.001), which was restored by oxygen supplementation (P < 0.001). We did not observe sex effects of urethane anesthesia on blood pressure, heart rate, heart rate variability, or [Formula: see text]. Taken together, these results underscore the importance of a cautious approach when using urethane in mice, as urethane significantly impacts arterial blood pressure, heart rate, oxygen saturation, and heart rate variability.NEW & NOTEWORTHY This investigation documents cardiovascular outcomes in mice receiving urethane anesthesia, emphasizing sex as a biological variable, and considering oxygen supplementation during anesthesia. This is the first report of M-curve analysis in rodents as a heart rate-independent variability analysis.

Sleep apnea syndrome associated with gonadal hormone imbalance (Review)

Patients with obstructive sleep apnea exhibit an increased risk of developing gonadal disorders. Because a notable number of people worldwide have sleep respiratory and reproductive disorders, it is essential to recognize the association between local upper airway dysfunction and its gonadal effects. Repeated breathing pauses cause sleep fragmentation, disorganization of sleep cycles and stages, sympathetic activation, intermittent hypoxemia and systemic inflammation. Nocturnal intermittent hypoxemia has a direct central effect on neurotransmitters, with disturbances in the normal production of hypothalamic-pituitary hormones. Awakenings and micro-awakenings at the end of apneic episodes produce a central stress responsible for hormonal changes and subsequent endocrine imbalances. The aim of the present study was to investigate the impact of obstructive sleep apnea syndrome (OSAS) on gonadal hormonal homeostasis and its consequences. Recognizing and understanding how local upper airway dysfunction causes gonadal imbalance may facilitate better care for patients with OSAS. Although there may be a direct relationship between sleep-disordered breathing and gonadal function mediated by hormones via the hypothalamic-pituitary-gonadal axis, to date, current therapies have not been effective.

Erythropoietin and caffeine exert similar protective impact against neonatal intermittent hypoxia: Apnea of prematurity and sex dimorphism

Apnea of prematurity (AoP) is associated with severe and repeated episodes of arterial oxygen desaturation (intermittent hypoxia - IH), which in turn increases the number of apneas. So far, there is no data addressing whether IH leads to sex-specific respiratory consequences, neither if drugs targeting AoP are more effective in males or females. We used rat pups for investigating whether IH-mediated increase of apneas is sex-specific. We also tested whether caffeine (treatment of choice of AoP), erythropoietin (Epo - a neuroprotective factor and potent respiratory stimulant), and combination of both (caffeine+Epo) prevent the IH-mediated formation of apneas in a sex-dependent manner. Newborn rats exposed to IH (21% - 10% FIO₂-8 h a day - 10 cycles per hour) during postnatal days (P) 3-10 were used in this work. Animals were administered drug vehicle, Epo, caffeine and Epo + caffeine (daily from P3 to P10) gavage. At P10 the frequency of apneas at rest (as an index of respiratory dysfunction induced by IH), and respiratory parameters were measured by plethysmography. Our results showed that IH significantly increases the number of apneas in male but not in female rat pups. Moreover, caffeine and Epo in males similarly prevented the increase of apneas induced by IH, and the administration of both drugs together did not provide a cumulative beneficial effect. No impact of drugs was evidenced in females. Apart from apneas, IH increased the normoxic basal ventilation (ventilation at rest) of male animals, and treatments did not prevent such alteration. Besides, no IH- nor treatment-mediated modulation of basal ventilation was found in the basal ventilation of female animals. Analysis of the activity of pro- and antioxidative molecules revealed that IH induces oxidative stress in the brainstem of male and female animals and that all tested treatments similarly prevented such oxidative imbalance in pups of both sexes. We concluded that neonatal IH and the treatments tested to prevent its respiratory consequences are sex-specific. The mechanics associated with such prevention are directly linked with the prevention of oxidative stress and the maturation of the brain. These findings are relevant to understanding better the AoP disorder and for proposing Epo as a new therapeutical tool.

Obstructive sleep apnea and hormones - a novel insight

Obstructive sleep apnea (OSA), a disorder characterized by repetitive collapse of the upper respiratory tract during sleep, occurs in about 4% of middle-aged men and 2% of women. The incidence of the disorder is rising due to an increase in obesity and ageing of the population. Patients with obstructive sleep apnea are at elevated risk of some endocrinal and metabolic disorders, which may lead to serious consequences including shortening of life expectancy. The recognition and understanding of interactions between local upper airway dysfunction and its endocrinal consequences is therefore vital. In this review we will focus on the influence of OSA on bone metabolism and endocrine homeostasis.

Membrane progesterone receptor-β, but not -α, in dorsal brain stem establishes sex-specific chemoreflex responses and reduces apnea frequency in adult mice

We tested the hypothesis that membrane progesterone receptors (mPR) contribute to respiratory control in adult male and female mice. Mice were implanted with osmotic minipumps for continuous infusion of small interfering RNA (siRNA) directed against mPRα, mPRβ, or a control solution in the fourth ventricle (to target brain stem respiratory areas) for 14 days. We then performed respiratory and metabolic recordings by whole body plethysmography at rest and in response to hypoxia (12% O2) or hypercapnia (5% CO2, 5 min each). For each treatment, we have verified with immunohistochemistry that the staining intensity of mPRα or mPRβ in the brain stem is decreased. At rest, the siRNA against mPRα and mPRβ increased respiratory frequency in males only. The siRNA against mPRβ almost tripled the frequency of apneas in male and in female mice, while the siRNA against mPRα had no effect. Regarding respiratory chemoreflex, the siRNA against mPRβ suppressed the response to hypoxia in male and female mice and reduced by ∼50% the response to hypercapnia, while the siRNA against mPRα had more limited effects. Interestingly, control females had higher ventilatory response to hypoxia and hypercapnia than males, and these sex-specific effects were suppressed by the siRNA against mPRβ, whereas they were still present after treatment with the siRNA against mPRα. We conclude that mPRβ reduces apnea frequency in male and female mice and establishes sex-specific ventilatory chemoreflex.

Sexual Dimorphism in the Regulation of Estrogen, Progesterone, and Androgen Receptors by Sex Steroids in the Rat Airway Smooth Muscle Cells

The role of sex hormones in lung is known. The three main sex steroid receptors, estrogen, progesterone, and androgen, have not been sufficiently studied in airway smooth muscle cells (ASMC), and the sex hormone regulation on these receptors is unknown. We examined the presence and regulation of sex hormone receptors in female and male rat ASMC by Western blotting and flow cytometry. Gonadectomized rats were treated with 17β-estradiol, progesterone, 17β-estradiol + progesterone, or testosterone. ASMC were enzymatically isolated from tracheas and bronchi. The experiments were performed with double staining flow cytometry (anti-α-actin smooth muscle and antibodies to each hormone receptor). ERα, ERβ, tPR, and AR were detected in females or males. ERα was upregulated by E2 and T and downregulated by P4 in females; in males, ERα was downregulated by P4, E + P, and T. ERβ was downregulated by each treatment in females, and only by E + P and T in males. tPR was downregulated by P4, E + P, and T in females. No hormonal regulation was observed in male receptors. AR was downregulated in males treated with E + P and T. We have shown the occurrence of sex hormone receptors in ASMC and their regulation by the sex hormones in female and male rats.

Neonatal stress affects the aging trajectory of female rats on the endocrine, temperature, and ventilatory responses to hypoxia

Human and animal studies on sleep-disordered breathing and respiratory regulation show that the effects of sex hormones are heterogeneous. Because neonatal stress results in sex-specific disruption of the respiratory control in adult rats, we postulate that it might affect respiratory control modulation induced by ovarian steroids in female rats. The hypoxic ventilatory response (HVR) of adult female rats exposed to neonatal maternal separation (NMS) is ∼30% smaller than controls (24), but consequences of NMS on respiratory control in aging female rats are unknown. To address this issue, whole body plethysmography was used to evaluate the impact of NMS on the HVR (12% O2, 20 min) of middle-aged (MA; ∼57 wk old) female rats. Pups subjected to NMS were placed in an incubator 3 h/day for 10 consecutive days (P3 to P12). Controls were undisturbed. To determine whether the effects were related to sexual hormone decline or aging per se, experiments were repeated on bilaterally ovariectomized (OVX) young (∼12 wk old) adult female rats. OVX and MA both reduced the HVR significantly in control rats but had little effect on the HVR of NMS females. OVX (but not aging) reduced the anapyrexic response in both control and NMS animals. These results show that hormonal decline decreases the HVR of control animals, while leaving that of NMS female animals unaffected. This suggests that neonatal stress alters the interaction between sex hormone regulation and the development of body temperature, hormonal, and ventilatory responses to hypoxia.