Effects of long-term dehydration on stress markers, blood parameters, and tissue morphology in the dromedary camel (Camelus dromedarius).

Introduction: Dromedary camels robustly withstand dehydration, and the rough desert environment but the adaptation mechanisms are not well understood. One of these mechanisms is that the dromedary camel increases its body temperature to reduce the process of evaporative cooling during the hot weather. Stress in general, has deleterious effects in the body. In this study, we sought to determine the effects of dehydration and rehydration on stress parameters in the dromedary camels and how it pacifies these effects. Methods: Nineteen male camels were randomly divided into control, dehydrated and rehydrated groups, and fed alfalfa hay ad-libitum. The dehydrated and rehydrated groups were water-restricted for 20 days after which the rehydrated camels were provided with water for 72 h. The control and dehydrated camels were slaughtered at day 20 from the start of experiment whereas the rehydrated group was killed 72 h later. Many biochemical, hematological histopathological parameters and gene analysis were performed in relevant tissues collected including blood, plasma, and tissues. Results and discussion: It was observed that severely dehydrated camels lost body weight, passed very hard feces, few drops of concentrated urine, and were slightly stressed as reflected behaviorally by loss of appetite. Physiologically, the stress of dehydration elicited modulation of plasma stress hormones for water preservation and energy supply. Our results showed significant increase in cortisol, norepinephrine and dopamine, and significant decrease in epinephrine and serotonin. The significant increase in malondialdehyde was accompanied with significant increase in antioxidants (glutathione, retinol, thiamin, tocopherol) to provide tissue protection from oxidative stress. The physiological blood changes observed during dehydration serve different purposes and were quickly restored to normality by rehydration. The dehydrated/rehydrated camels showed reduced hump size and serous atrophy of perirenal and epicardial fat. The latter changes were accompanied by significantly increased expression of genes encoding proteins for energy production (ANGPTL4, ACSBG1) from fat and significantly decreased expression of genes (THRSP; FADS 1&2) encoding proteins enhancing energy expenditure. This process is vital for camel survival in the desert. Dehydration induced no major effects in the vital organs. Only minor degenerative changes were observed in hepatic and renal cells, physiological cardiomyocyte hypertrophy in heart and follicular hyperplasia in splenic but lipidosis was not depicted in liver hepatocytes. Ketone bodies were not smelled in urine, sweat and breathing of dehydrated animals supporting the previous finding that the ß hydroxybutyrate dehydrogenase, a key enzyme in ketone body formation, is low in the camel liver and rumen. Rehydration restored most of blood and tissues to normal or near normal. In conclusion, camels are adapted to combat dehydration stress and anorexia by increasing anti-stressors and modulating genes involved in fat metabolism.

Expression and location of HSP60 and HSP10 in the heart tissue of heat-stressed rats.

The present study aimed to analyze the expression levels and localizations of heat shock protein (HSP) 60 and HSP10 in the heart tissue of rats subjected to heat stress (42°C) for 0, 20, 80 and 100 min. Histopathological injuries and increased serum activities of serum lactate dehydrogenase and creatine kinase isoenzyme MB were detected in the heated rat myocardial cells. These results suggested that heat stress-induced acute degeneration may be sufficient to cause sudden death in animals by disrupting the function and permeability of the myocardial cell membrane. In addition, the expression levels of HSP60 were significantly increased following 20 min heat stress, whereas the expression levels of its cofactor HSP10 were not. Furthermore, the location of HSP60, but not of HSP10, was significantly altered during periods of heat stress. These results suggested that HSP60 in myocardial tissue may be more susceptive to the effects of heat stress as compared with HSP10, and that HSP10 is constitutively expressed in the heart of rats. The expression levels and localizations of HSP60 and HSP10 at the different time points of heat stress were not similar, which suggested that HSP60 and HSP10 may not form a complex in the heart tissue of heat-stressed rats.

Localization and expression of heat shock protein 70 with rat myocardial cell damage induced by heat stress in vitro and in vivo.

The aim of the present study was to investigate the association between heat shock protein (Hsp) 70 expression kinetics and heat stress­induced damage to rat myocardial cells in vitro and in vivo. The results showed that the activity of heart injury­associated enzymes, including aspartate aminotransferase and creatine kinase, significantly increased and myocardial cells developed acute histopathological lesions; this therefore suggested that heat stress altered the integrity of myocardial cells in vitro and in vivo. Levels of Hsp70 in vitro decreased following the initiation of heat stress and then steadily increased until heat stress ceased at 100 min; however, in vivo studies demonstrated a gradual increase in Hsp70 levels in the heart cells of rats from the initiation of heat stress, followed by a sharp decline at 100 min. These results indicated that the cells sustained different degrees of injury in vivo compared with those sustained in vitro, this may be due to different regulatory mechanisms in the two environments. Intracytoplasmic Hsp70 signaling was significantly reduced at 60 min in vitro, compared with that of the in vivo study, indicating that Hsp70 consumption may have exceeded its production prior to 60 min of heat stress, and following 60 min the cells produced sufficient Hsp70 protein for their protection against heat stress. Hsp70­positive signals in the cytoplasm of heart cells in vivo were more prominent in the intact areas compared with those of the degenerated areas and the density of Hsp70­positive signals was significantly reduced following 60 min of heat stress. In conclusion, comprehensive comparisons of enzymes, cell morphology and Hsp70 levels indicated that decreased levels of Hsp70 were associated with the reduced protective effect on myocardial cells in vitro and in vivo.

Comparative analysis of αB-crystallin expression in heat-stressed myocardial cells in vivo and in vitro.

Relationships between αB-crystallin expression patterns and pathological changes of myocardial cells after heat stress were examined in vitro and in vivo in this study using the H9C2 cell line and Sprague-Dawley rats, respectively. Histopathological lesions, characterized by acute degeneration, karyopyknosis and loss of a defined nucleus, became more severe in rat hearts over the course of heat stress treatment from 20 min to 100 min. The expression of αB-crystallin in rat hearts showed a significant decrease (P<0.05) throughout the heat stress treatment period, except at the 40 min time point. Likewise, decreased αB-crystallin expression was also observed in the H9C2 cell line exposed to a high temperature in vitro, although its expression recovered to normal levels at later time points (80 and 100 min) and the cellular damage was less severe. The results suggest that αB-crystallin is mobilized early after exposure to a high temperature to interact with damaged proteins but that the myocardial cells cannot produce sufficient αB-crystallin for protection against heat stress. Lower αB-crystallin expression levels were accompanied by obvious cell/tissue damage, suggesting that the abundance of this protein is associated with protective effects in myocardial cells in vitro and in vivo. Thus, αB-crystallin is a potential biomarker of heat stress.

Localization and expression of Hsp27 and αB-crystallin in rat primary myocardial cells during heat stress in vitro.

Neonatal rat primary myocardial cells were subjected to heat stress in vitro, as a model for investigating the distribution and expression of Hsp27 and αB-crystallin. After exposure to heat stress at 42°C for different durations, the activities of enzymes expressed during cell damage increased in the supernatant of the heat-stressed myocardial cells from 10 min, and the pathological lesions were characterized by karyopyknosis and acute degeneration. Thus, cell damage was induced at the onset of heat stress. Immunofluorescence analysis showed stronger positive signals for both Hsp27 and αB-crystallin from 10 min to 240 min of exposure compared to the control cells. According to the Western blotting results, during the 480 min of heat stress, no significant variation was found in Hsp27 and αB-crystallin expression; however, significant differences were found in the induction of their corresponding mRNAs. The expression of these small heat shock proteins (sHsps) was probably delayed or overtaxed due to the rapid consumption of sHsps in myocardial cells at the onset of heat stress. Our findings indicate that Hsp27 and αB-crystallin do play a role in the response of cardiac cells to heat stress, but the details of their function remain to be investigated.