The effect of acute heat exposure on rat pituitary corticotroph activation: the role of vasopressin

Identification of Novel mRNA Isoforms Associated with Acute Heat Stress Response Using RNA Sequencing Data in Sprague Dawley Rats

The molecular mechanisms underlying heat stress tolerance in animals to high temperatures remain unclear. This study identified the differentially expressed mRNA isoforms which narrowed down the most reliable DEG markers and molecular pathways that underlie the mechanisms of thermoregulation. This experiment was performed on Sprague Dawley rats housed at 22 °C (control group; CT), and three acute heat-stressed groups housed at 42 °C for 30 min (H30), 60 min (H60), and 120 min (H120). Earlier, we demonstrated that acute heat stress increased the rectal temperature of rats, caused abnormal changes in the blood biochemical parameters, as well as induced dramatic changes in the expression levels of genes through epigenetics and post-transcriptional regulation. Transcriptomic analysis using RNA-Sequencing (RNA-Seq) data obtained previously from blood (CT and H120), liver (CT, H30, H60, and H120), and adrenal glands (CT, H30, H60, and H120) was performed. The differentially expressed mRNA isoforms (DEIs) were identified and annotated by the CLC Genomics Workbench. Biological process and metabolic pathway analyses were performed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. A total of 225, 5764, and 4988 DEIs in the blood, liver, and adrenal glands were observed. Furthermore, the number of novel differentially expressed transcript lengths with annotated genes and novel differentially expressed transcript with non-annotated genes were 136 and 8 in blood, 3549 and 120 in the liver, as well as 3078 and 220 in adrenal glands, respectively. About 35 genes were involved in the heat stress response, out of which, Dnaja1, LOC680121, Chordc1, AABR07011951.1, Hsp90aa1, Hspa1b, Cdkn1a, Hmox1, Bag3, and Dnaja4 were commonly identified in the liver and adrenal glands, suggesting that these genes may regulate heat stress response through interactions between the liver and adrenal glands. In conclusion, this study would enhance our understanding of the complex underlying mechanisms of acute heat stress, and the identified mRNA isoforms and genes can be used as potential candidates for thermotolerance selection in mammals.

The Effects of Long-Term Exposure to Moderate Heat on Rat Pituitary ACTH Cells: Histological and Hormonal Study

Global warming causes an increased ambient temperature and prolonged heatwaves during the summer, which represent stressogenic factors affecting the hypothalamo-pituitary-adrenocortical (HPA) axis in mammals. The aim of this study was to investigate the effects of long-term (7-60 days) exposure to moderately elevated ambient temperature (35 ± 1°C) on the histological aspect and secretory ability of pituitary adrenocorticotropic (ACTH) cells, as well as on the corticosterone output, in adult rats. Stereological parameters of ACTH cells were estimated upon immunohistochemistry. The blood concentrations of ACTH and corticosterone were determined by immunoassays. The volume of ACTH cells in rats exposed to moderately high temperature for 7, 14, 21, 30 and 60 days decreased (p<0.05) by 18.1%, 14.5%, 13.5%, 8.6% and 14.2% respectively, compared to the same parameter in the controls. The volume density of ACTH cells in the groups exposed to elevated temperature for 7, 14, 21, 30 and 60 days decreased (p<0.05) by 40.0%, 33.3%, 26.7%, 13.3% and 26.7% respectively, in comparison with control rats. The plasma concentration of ACTH varied differently (p<0.05) with the duration of exposure to the elevated temperature. The serum concentration of corticosterone was decreased (p<0.05) by 54.9%, 24.4%, 29.9%, 21.1% and 24.4% in groups subjected to moderately high temperature for 7, 14, 21, 30 and 60 days respectively, all compared to the control value. Despite some signs of functional recovery of ACTH cells during the treatment, the impression is that the long-term character of this stressor overcomes the capacity of the HPA axis for resistance.

Pituitary Remodeling Throughout Life: Are Resident Stem Cells Involved?

The pituitary gland has the primordial ability to dynamically adapt its cell composition to changing hormonal needs of the organism throughout life. During the first weeks after birth, an impressive growth and maturation phase is occurring in the gland during which the distinct hormonal cell populations expand. During pubertal growth and development, growth hormone (GH) levels need to peak which requires an adaptive enterprise in the GH-producing somatotrope population. At aging, pituitary function wanes which is associated with organismal decay including the somatopause in which GH levels drop. In addition to these key time points of life, the pituitary's endocrine cell landscape plastically adapts during specific (patho-)physiological conditions such as lactation (need for PRL) and stress (engagement of ACTH). Particular resilience is witnessed after physical injury in the (murine) gland, culminating in regeneration of destroyed cell populations. In many other tissues, adaptive and regenerative processes involve the local stem cells. Over the last 15 years, evidence has accumulated that the pituitary gland houses a resident stem cell compartment. Recent studies propose their involvement in at least some of the cell remodeling processes that occur in the postnatal pituitary but support is still fragmentary and not unequivocal. Many questions remain unsolved such as whether the stem cells are key players in the vivid neonatal growth phase and whether the decline in pituitary function at old age is associated with decreased stem cell fitness. Furthermore, the underlying molecular mechanisms of pituitary plasticity, in particular the stem cell-linked ones, are still largely unknown. Pituitary research heavily relies on transgenic in vivo mouse models. While having proven their value, answers to pituitary stem cell-focused questions may more diligently come from a novel powerful in vitro research model, termed organoids, which grow from pituitary stem cells and recapitulate stem cell phenotype and activation status. In this review, we describe pituitary plasticity conditions and summarize what is known on the involvement and phenotype of pituitary stem cells during these pituitary remodeling events.

Influence of long-term thermal stress on the in vitro maturation on embryo development and Heat Shock Protein abundance in zebu cattle

The objective of this study was to investigate the influence of long-term temperature stress during the in vitro maturation (IVM) of oocytes on the in vitro embryo production (IVP) and the abundance of HSP70 and HSP90 in zebu cattle. Viable cumulus-oocyte complexes (COCs) were incubated for 24 h at 37 °C, 38.5 °C, or 40 °C for the low-, physiological, and high-temperature stress treatments, respectively. Thereafter, they were subjected to in vitro fertilization and culture. Temperature did not affect the polar body extrusion. However, IVP was adversely affected when IVM took place at 37 °C and 40 °C. The highest abundance of HSP70 was observed in cumulus cells after maturation of COCs at 40 °C. In contrast, HSP70 was more abundant in oocytes at both 37 °C and 40 °C; however, at 40 °C, the difference to the control group (38.5 °C) was not significant. In contrast, the highest abundance of HSP90 was observed in oocytes and cumulus cells at 37 °C. It appears that HSP70 and HSP90 respond to cold and heat stress in different ways. In conclusion, moderately high (40 °C) and low (37 °C) thermal stress for 24 h during IVM is detrimental to the developmental competence of oocyte and is accompanied by changes in the abundances of HSP70 and HSP90, especially in cumulus cells.

Corticosterone tissue-specific response in Sprague Dawley rats under acute heat stress

Our study evaluated the physiological responses to acute heat stress in rats via body temperature and tissue corticosterone levels, and investigated the relative tissue response to heat stress based on corticosterone. Body temperature of rats under 22 °C (control) and 42 °C for 30 (H30), 60 (H60) and 120 min (H120) was measured. Correspondingly, corticosterone was analyzed in 11 tissues (adrenal, brain, heart, kidney, liver, lung, leg muscle, blood, stomach, spleen and small intestine). Analysis of variance and correlations were conducted on body temperature and corticosterone levels. The receiver operating characteristic (ROC) analyzed the thermo-sensitivity via corticosterone. Body temperature of rats in H30, H60 and H120 groups were higher (P < 0.05) than the control. Compared to the control, corticosterone levels of heart, stomach and small intestine at H30, corticosterone levels in adrenal, leg muscle and stomach at H60, and corticosterone levels in adrenal, heart, lung, stomach and small intestine at H120 differed (P < 0.05). The corticosterone in lung tissue was an excellent indicator of acute heat stress, with an area under the curve (AUC) of 1.00 at H60 and H120. In order to improve the prediction of acute heat stress, models combining corticosterone levels of multiple tissues reached an AUC of 1.00 for H30, and the sensitivity increased to 100% for H60 and H120. In conclusion, changes in the patterns and thermosensitivity of corticosterone levels associated with the duration of heat stress across body tissues were evidenced. The single and multi-organizational corticosterone models serve as indicators for evaluating heat stress across different time periods.

The Effect of Moderate Heat on Rat Pituitary ACTH Cells: Histomorphometric, Immunofluorescent and Hormonal Study

In areas with moderate continental climate, increased average ambient temperature during the summer represents a stressogenic factor that affects the hypothalamo-pituitaryadrenocortical axis in mammals. Therefore, we wanted to examine the effects of 4 days of constant exposure to moderately elevated ambient temperature (35 ± 1oC) on the histomorphometric and immunofl uorescent characteristics, as well as on the hormonal secretion of pituitary corticotropes (ACTH) cells in adult male rats. In comparison with the controls kept at 20 ± 2oC, a signifi cant increase (p<0.05) of the absolute and relative pituitary weight (23.1% and 36.1%, respectively) was registered after exposure to heat. The localization, as well as the shape of the ACTH cells in the heat exposed group was not signifi cantly altered, but their immunopositivity was weaker. After 4 days of heat exposure, a weaker signal confi rmed the relative fl uorescence intensity of the ACTH cells (15.3%, p<0.05). In heat exposed rats, an increase of the cellular and nuclear volumes of immunolabelled ACTH cells and decrease of their volume density (6.9%, 14.3% and 20.0%, respectively; p<0.05) was registered. Observed histomorphometric and immunofl uorescent features of the pituitary ACTH cells were in accordance with the increased (p<0.05) value of plasma adrenocorticotropic hormone (ACTH) by 23.7% compared to the control rats. It can be concluded that the 4-day exposure to moderately elevated ambient temperature intensifi es pituitary ACTH secretion in adult male rats.

Determinants of plasma copeptin: a systematic investigation in a pediatric mechanical ventilation model

Copeptin, the C-terminal part of the arginine vasopressin precursor peptide, holds promise as a diagnostic and prognostic plasma biomarker in various acute clinical conditions. Factors influencing copeptin response in the critical care setting are only partially established and have not been investigated systematically. Using an in vivo infant ventilation model (Wistar rats, 14 days old), we studied the influence of commonly occurring stressors in critically ill children. In unstressed ventilated rats basal median copeptin concentration was 22pmol/L. In response to respiratory alkalosis copeptin increased 5-fold, while exposure to hypoxemia, high PEEP, hemorrhage, and psycho-emotional stress produced a more than 10-fold increase. Additionally, we did not find a direct association between copeptin and acidosis, hypercapnia, and hyperthermia. Clinicians working in the acute critical care setting should be aware of factors influencing copeptin plasma concentrations. Moreover, our results do have implications for animal studies in the field of stress research.