Prenatal hypoxia increases blood pressure in male rat offspring and affects their response to artificial light at night

Artificial light at night affects the daily profile of pulse pressure and protein expression in the thoracic aorta of rats

Artificial light at night (ALAN) disrupts 24-h variability of blood pressure, but the molecular mechanisms underlying these effects are unknown. Therefore, we analysed the daily variability of pulse pressure, the maximum value of acceleration rate of aortic pressure (dP/dt(max)) measured by telemetry and protein expression in the thoracic aorta of normotensive male rats exposed to ALAN (1-2 lx) for 3 weeks. Daily, 24-h variability of pulse pressure and dP/dt(max) was observed during a regular light/dark regimen with higher values during the dark compared to the light phase of the day. ALAN suppressed 24-h variability and enhanced ultradian (<12-h) periods of pulse pressure and dP/dt(max) in duration-dependent manners. From beat-to-beat blood pressure variability, ALAN decreased low-frequency bands (a sympathetic marker) and had minimal effects on high-frequency bands. At the molecular level, ALAN decreased angiotensin II receptor type 1 expression and reduced 24-h variability. ALAN caused the appearance of 12-h oscillations in transforming growth factor β1 and fibulin 4. Expression of sarco/endoplasmic reticulum Ca2+-ATPase type 2 was increased in the middle of the light and dark phase of the day, and ALAN did not affect its daily and 12-h variability. In conclusion, ALAN suppressed 24-h variability of pulse pressure and dP/dt(max), decreased the power of low-frequency bands and differentially affected the expression of specific proteins in the rat thoracic aorta. Suppressed 24-h oscillations by ALAN underline the pulsatility of individual endocrine axes with different periods, disrupting the cardiovascular control of central blood pressure.

Artificial light at night suppresses the day-night cardiovascular variability: evidence from humans and rats

Artificial light at night (ALAN) affects most of the population. Through the retinohypothalamic tract, ALAN modulates the activity of the central circadian oscillator and, consequently, various physiological systems, including the cardiovascular one. We summarised the current knowledge about the effects of ALAN on the cardiovascular system in diurnal and nocturnal animals. Based on published data, ALAN reduces the day-night variability of the blood pressure and heart rate in diurnal and nocturnal animals by increasing the nocturnal values of cardiovascular variables in diurnal animals and decreasing them in nocturnal animals. The effects of ALAN on the cardiovascular system are mainly transmitted through the autonomic nervous system. ALAN is also considered a stress-inducing factor, as glucocorticoid and glucose level changes indicate. Moreover, in nocturnal rats, ALAN increases the pressure response to load. In addition, ALAN induces molecular changes in the heart and blood vessels. Changes in the cardiovascular system significantly depend on the duration of ALAN exposure. To some extent, alterations in physical activity can explain the changes observed in the cardiovascular system after ALAN exposure. Although ALAN acts differently on nocturnal and diurnal animals, we can conclude that both exhibit a weakened circadian coordination among physiological systems, which increases the risk of future cardiovascular complications and reduces the ability to anticipate stress.

Decreased sympathetic nerve activity in young hypertensive rats reared by normotensive mothers

AIMS

Early postnatal development can be significantly compromised by changes in factors provided by the mother, leading to increased vulnerability to hypertension in her offspring. TGR(mRen-2)27 (TGR) mothers, characterised by an overactivated renin-angiotensin system, exhibit altered ion composition in their breast milk. Therefore, we aimed to analyse the impact of cross-fostering on cardiovascular parameters in hypertensive TGR and normotensive Hannover Sprague-Dawley (HanSD) offspring.

MATERIALS AND METHODS

We measured cardiovascular parameters in 5- to 10-week-old male offspring by telemetry. The expression of proteins related to vascular function was assessed by western blotting in the aortic samples obtained from 6- to 12-week-old male offspring. Plasma renin activity and plasma angiotensin II (Ang II) levels were evaluated by radioimmunoassay (RIA).

KEY FINDINGS

The development of hypertension was in TGR accompanied by increased low-to-high frequency ratio (LF/HF; a marker of sympathovagal balance; 0.51 ± 0.16 in week 10). Furthermore, TGR exhibited increased aortic expression of mineralocorticoid receptor (MR; p < 0.05) and transforming growth factor beta type 1 (TGF-β1; p = 0.002) compared to HanSD offspring. Fostering significantly decreased sympathovagal balance (0.23 ± 0.10 in week 10) and, transiently, plasma Ang II levels and MR expression in TGR offspring reared by HanSD mothers.

SIGNIFICANCE

These findings highlight the importance of understanding the complex interplay between early life experiences, maternal factors, and later cardiovascular function. Understanding the mechanisms behind the observed effects may help to identify potential interventions to prevent the development of hypertension later in life.

Perinatal intermittent hypoxia increases early susceptibility to ANG II-induced hypertension in adult male but not in female Sprague-Dawley rats

Prenatal, perinatal, and adulthood exposure to chronic intermittent hypoxia (IH) increases blood pressure in rodents. Males exposed to chronic IH have higher blood pressure versus females. However, it is unknown if this same-sex difference exists with acute perinatal IH. We tested the hypothesis that acute perinatal IH increases baseline blood pressure and enhances sensitivity to angiotensin II (ANG II)-induced hypertension in male Sprague-Dawley rats. Male and female pups were randomized to control (room air) or IH (10 min of ∼10% O2 for 3 times/day) for the first 8 days of life. IH decreased oxygen saturation, as confirmed via a pulse oximeter. Pups were weaned at postnatal day 21. Blood pressure was measured via telemetry beginning at 14 wk of age and analyzed separately into light and dark phases to assess circadian rhythm. Osmotic minipumps to deliver ANG II were implanted at 15 wk of age. Perinatal IH exposure did not alter baseline blood pressure. One week of ANG II treatment increased blood pressure in light and dark periods in males exposed to IH versus control; there was no effect in females. Blood pressure among the groups was comparable following 2 wk of ANG II infusion. Perinatal IH did not change the circadian rhythm. Following ANG II treatment, indexes of renal injury were measured. Perinatal IH did not alter kidney size, structure, nephron number, or creatinine clearance. These data indicate that acute perinatal IH enhances early ANG II-induced hypertension in males, independent of nephron loss or decreases in body weight or kidney function.NEW & NOTEWORTHY The impact of acute intermittent hypoxia (IH) in early life on blood pressure in adulthood is unknown. This study used a new model exposing female and male rat pups to acute IH in the first 8 days of life, without exposing the dam. Although baseline blood pressure was not altered in adulthood, IH increased susceptibility to angiotensin II hypertension only in males, supporting increased susceptibility of males exposed to IH to a second cardiovascular stressor.

Hypotensive effects of melatonin in rats: Focus on the model, measurement, application, and main mechanisms

The hypotensive effects of melatonin are based on a negative correlation between melatonin levels and blood pressure in humans. However, there is a positive correlation in nocturnal animals that are often used as experimental models in cardiovascular research, and the hypotensive effects and mechanism of melatonin action are often investigated in rats and mice. In rats, the hypotensive effects of melatonin have been studied in normotensive and spontaneously or experimentally induced hypertensive strains. In experimental animals, blood pressure is often measured indirectly during the light (passive) phase of the day by tail-cuff plethysmography, which has limitations regarding data quality and animal well-being compared to telemetry. Melatonin is administered to rats in drinking water, subcutaneously, intraperitoneally, or microinjected into specific brain areas at different times. Experimental data show that the hypotensive effects of melatonin depend on the experimental animal model, blood pressure measurement technique, and the route, time and duration of melatonin administration. The hypotensive effects of melatonin may be mediated through specific membrane G-coupled receptors located in the heart and arteries. Due to melatonin's lipophilic nature, its potential hypotensive effects can interfere with various regulatory mechanisms, such as nitric oxide and reactive oxygen species production and activation of the autonomic nervous and circadian systems. Based on the research conducted on rats, the cardiovascular effects of melatonin are modulatory, delayed, and indirect.

Prenatal Hypoxia Affects Foetal Cardiovascular Regulatory Mechanisms in a Sex- and Circadian-Dependent Manner: A Review

Prenatal hypoxia during the prenatal period can interfere with the developmental trajectory and lead to developing hypertension in adulthood. Prenatal hypoxia is often associated with intrauterine growth restriction that interferes with metabolism and can lead to multilevel changes. Therefore, we analysed the effects of prenatal hypoxia predominantly not associated with intrauterine growth restriction using publications up to September 2021. We focused on: (1) The response of cardiovascular regulatory mechanisms, such as the chemoreflex, adenosine, nitric oxide, and angiotensin II on prenatal hypoxia. (2) The role of the placenta in causing and attenuating the effects of hypoxia. (3) Environmental conditions and the mother's health contribution to the development of prenatal hypoxia. (4) The sex-dependent effects of prenatal hypoxia on cardiovascular regulatory mechanisms and the connection between hypoxia-inducible factors and circadian variability. We identified that the possible relationship between the effects of prenatal hypoxia on the cardiovascular regulatory mechanism may vary depending on circadian variability and phase of the days. In summary, even short-term prenatal hypoxia significantly affects cardiovascular regulatory mechanisms and programs hypertension in adulthood, while prenatal programming effects are not only dependent on the critical period, and sensitivity can change within circadian oscillations.

Artificial light at night suppresses the expression of sarco/endoplasmic reticulum Ca2+ -ATPase in the left ventricle of the heart in normotensive and hypertensive rats

NEW FINDINGS

What is the central question of this study? Artificial light at night decreases blood pressure and heart rate in rats. Are these changes in heart rate accompanied by changes in protein expression in the heart's left ventricle? What is the main finding and its importance? Five weeks of artificial light at night affected protein expression in the heart's left ventricle in normotensive and hypertensive rats. Artificial light at night decreased expression of the sarco/endoplasmic reticulum Ca²⁺ -ATPase, angiotensin II receptor type 1 and endothelin-1.

ABSTRACT

Artificial light at night (ALAN) affects the circadian rhythm of the heart rate in normotensive Wistar rats (WT) and spontaneously hypertensive rats (SHR) through the autonomic nervous system, which regulates the heart's activity through calcium handling, an important regulator in heart contractility. We analysed the expression of the sarco/endoplasmic reticulum Ca²⁺ -ATPase (SERCA2) and other selected regulatory proteins involved in the regulation of heart contractility, angiotensin II receptor type 1 (AT₁ R), endothelin-1 (ET-1) and tyrosine hydroxylase (TH), in the left ventricle of the heart in WT and SHR after 2 and 5 weeks of ALAN with intensity 1-2 lx. Expression of SERCA2 was decreased in WT (control: 0.53 ± 0.07; ALAN: 0.46 ± 0.10) and SHR (control: 0.72 ± 0.18; ALAN: 0.56 ± 0.21) after 5 weeks of ALAN (P = 0.067). Expression of AT₁ R was significantly decreased in WT (control: 0.51 ± 0.27; ALAN: 0.34 ± 0.20) and SHR (control: 0.38 ± 0.07; ALAN: 0.23 ± 0.09) after 2 weeks of ALAN (P = 0.028) and in SHR after 5 weeks of ALAN. Expression of ET-1 was decreased in WT (control: 0.51 ± 0.27; ALAN: 0.28 ± 0.12) and SHR (control: 0.54 ± 0.10; ALAN: 0.35 ± 0.23) after 5 weeks of ALAN (P = 0.015). ALAN did not affect the expression of TH in WT or SHR. In conclusion, ALAN suppressed the expression of SERCA2, AT₁ R and ET-1, which are important for the regulation of heart contractility, in a strain-dependent pattern in both WT and SHR.