The stress response is a natural mammalian process begun by the stimulus of different situations such as isolation, crowded environments, different light/dark regimens, and varying durations of given intensities of lighting. Any discussion of the effects of several stressors on animal physiology encounters the problem of defining how animals cope with stress. The release of stress-response hormones and cytokines is only one facet of stress reactions’ complexity. The modulation of receptors, circulation of hormone transport-binding proteins and infiltrating macrophages, and intercommunication of hormone secretion pituitary cells lead to the stress response and modify regulatory processes. Research has clarified the neurocircuitry underlying the effects of corticotropin-releasing hormone on the hypothalamic–pituitary– adrenocortical axis and sympathetic adreno-medullary system (23, 35). The activation of the sympathetic nervous system and adrenal function has been seen in signs exhibited by rats kept in social isolation, alone and in a crowded environment and is a finding reported in several studies (12, 16, 23).
Reactive oxygen species (ROS) are produced by living organisms as a consequence of normal cellular metabolism and exposure to environmental oxidants such as microbial infections, extensive exercise, or pollutants and toxins such as ozone, pesticides, UV radiation and smoke. Large ROS accumulation is associated with adverse modifications of cellular components such as lipids, proteins, and DNA, and is a contributing cause of cancer, high blood pressure, neurological disorders, atherosclerosis, asthma, and diabetes. Both endogenous and exogenous defences are effective against oxidative stress, but the endogenous defence mechanism may not be sufficient to totally protect against the effects of ROS. Deleterious effects of oxidative stress arise from an imbalance between production of ROS and the capacity of the antioxidant mechanism. If the antioxidant mechanisms in an organism are insufficient, exogenous antioxidant supplements should be added to the diet for better health. Supplementation is a means of combatting oxidative stress both in humans and animals. The exogenous defence mechanism comes from the diet in the form of antioxidants, especially from natural antioxidants as phytochemicals in vegetables, fruits, flowers and traditional medicinal plants. The importance of natural antioxidants is being increasingly often investigated in oxidative–antioxidative balance and wellness because of consumer concern regarding the safety of synthetic antioxidants, and because of the low cost and high capacity for H+ donation of natural antioxidants (15). Besides endogenous antioxidants, exogenous antioxidants are essential to mitigate the harm of oxidative stress, and they must obviously be consumed in amounts sufficient to deliver their intended effect. It was reported that there is a correlation between total antioxidant capacity and consumption of herbs (5). Total antioxidant capacity (TAC) denotes the total effect of all antioxidants in a studied organism and analogously, total oxidant status (TOS) does so regarding the effect of all oxidants. In studies investigating TAC and TOS, it is pertinent to also evaluate paraoxonase-1 (PON1), an antioxidant enzyme that is produced by the liver. Paraoxonase-1 has a role in decreasing oxidative stress. It was explained that as inflammation progresses in the response of the organism to oxidative stress, the TOS and TAC values increase, and PON1 decreases (4, 29).
Cytokines are produced in reaction to physiological challenges which are expressed by white blood cell levels (23, 33). It was shown that cytokines have a wide range of effects on the organism, including fever, inflammation, and promotion of wound healing. Excessive or insufficient production of cytokines is related to the pathophysiology of a range of diseases and conditions, stress among them (14, 31). Stress is accompanied by altered production of inflammatory cytokines and neuropeptides in the central nervous system. Contradictory results have been indicated for the relationship between stress and cytokines such as interleukins 2, 4 and 6 (IL-2, IL-4, and IL-6), and interferon gamma (IFN-ɣ). Some researchers reported a decrease in IL-2 during stress (21), while others found an increase (6). It was also reported that IL-4 production could be increased, decreased or unchanged by stress (6, 25, 38). Some studies conducted on rats and mice showed higher IL-6 levels under stress circumstances (3). In contrast to some of the findings for IL-2, IL-4, and IL-6, it was reported that stress suppressed the production of IFN-ɣ (19).
Natural antioxidants and their products have vast potential to benefit health if introduced to human and animal nourishment. Understanding natural antioxidants in the context of oxidative stress, and translation of this knowledge into improvement of animal and human health are significant challenges.
The purpose of this study was to assess the influence of a diet supplemented with
Rats were given
The C and S groups only received the vehicle (tap water, 1 cc/day) by orogastric gavage for 28 days.
For the last two weeks, all animals experienced a light : dark cycle of 18 h : 6 h with changes at 7:00 and 01:00, modified from precedents in the literature (13, 27, 34). In these weeks, besides the rats in the S and SpS groups being fed with
Isolation stress was applied during the third week of the study to the S and SpS groups. The rats were kept in a separate cage for 30 min on Monday, Wednesday, Friday, and Sunday. Neither food nor water was given to the rats during this stress application.
Crowded environment stress was applied during the fourth week of the study to the S and SpS groups by placing six rats in a cage of a size specified for only three for 30 min on Tuesday, Thursday, and Saturday. As was the case for the previous stress, neither food nor water was given to the rats during this stress application.
Blood samples were centrifuged on the same day to separate the serum, and then the serum samples were kept at −80°C until the analysis. The serum TOS, TAC and PON1 values were measured with commercial kits (Rel Assay Diagnostics kits; Mega Tip, Gaziantep, Turkey) by using colorimetric methods and a UV2600-VIS spectrophotometer (Shimadzu, Kyoto, Japan).
Serum corticosterone (Elabscience, Houston, TX, USA), IL-2, IL-4 and IFN-ɣ were measured using a commercially available rat ELISA kit (ThermoFisher Scientific, Waltham, MA, USA). Assays were performed colorimetrically using a microplate reader (Biotek, Epoch, USA).
Our results showed that the levels of serum corticosterone significantly increased in the S group when compared to the C group (Fig. 1A; 46.02 ± 1.72 ng/mL and 57.03 ± 1.84 ng/mL, respectively, indicating a 24% rise). This indicates stress was induced successfully. However, feeding with
Percentage change in the parameters indicative of stress response in the groups used for the study. A – mean serum corticosterone level: control
All data are presented as the mean ± SD (n = 9); * – P < 0.05 when compared with control rat values; # – P < 0.05 when compared with stress-induced rat values
A significant decrease in the mean TAC levels was observed in stress-induced and unsupplemented rats compared with those in control animals (Fig. 1B). Microalga-supplemented rats showed remarkable improvements in TAC levels as compared to stress-induced rats fed only the basal diet. However, there were no statistical differences found in TOS (Fig. 1C), PON1 (Fig. 1D) or OSI (Fig. 1E) values among the groups.
The IL-2, IL-4, and IFN-ɣ parameters and their percentages are shown in Fig. 2. Although not significantly different when compared to control rats, IL-2 and IFN-ɣ were lower in stress-induced animals. Feeding with
Effect of supplementation with
All data are presented as the mean ± SD (n = 9)
Effect of supplementation with
Organ weights (g) | Groups |
|||
---|---|---|---|---|
Control (C) | Stress (S) | |||
Brain | 1.76 ± 0.06 | 1.75 ± 0.13 | 1.71 ± 0.19 | 1.73 ± 0.10 |
Heart | 1.05 ± 0.05 | 1.03 ± 0.09 | 1.02 ± 0.08 | 1.03 ± 0.14 |
Intestines | 25.15 ± 2.25 | 24.21 ± 3.36 | 25.84 ± 1.00 | 25.18 ± 2.35 |
Kidney | 2.63 ± 0.17 | 2.58 ± 0.33 | 2.67 ± 0.11 | 2.71 ± 0.43 |
Liver | 12.09 ± 1.42 | 11.93 ± 1.34 | 11.94 ± 0.67 | 11.89 ± 1.63 |
Spleen | 0.67 ± 0.07 | 0.66 ± 0.03 | 0.65 ± 0.05 | 0.67 ± 0.03 |
Stomach | 4.04 ± 1.38 | 3.95 ± 0.70 | 5.18 ± 1.01 | 4.93 ± 0.83 |
In this study, we evaluated the association between feeding male rats with
Stress responses have been linked to physiological conditions: besides the aforementioned serum corticosterone levels, they have been correlated with oxidative stress/antioxidant balance and cytokine levels. Serum corticosterone levels were significantly higher after induced mixed stress. Similar results were observed by Jameel
Oxidative stress is a result of an increased generation of free radicals and/or reduced physiological activity of antioxidant defence against free radicals. Regarding the influence of
Stress situations such as crowded environments or small cage sizes are also consequential for physical activity, feeding, and growth. It was reported that crowded environment stress suppressed rats’ organ development and thereby their growth (2). This suppression is also explained by basal metabolism and hormonal profiles (40). In the present study, although no significant changes were observed, there was a decrease in some organ weights (brain, heart, intestines, kidney, liver, spleen, and stomach) in the S group compared to the C group.
The constant rise in the global human population threatens biodiversity and worsens air and water pollution. These negative consequences impact animal and human health in undesirable ways and disrupt homeostasis, and in this aspect may be regarded as stressors. Physicochemical stress can be caused by environmental agents and is manifested as chronic infections, autoimmune diseases, and other physiological disorders. Besides the aforementioned ramifications of environmental changes as threats to homeostasis, additional threats to it are several easily transmittable zoonoses. Because of these pathogenic risks, an organism’s capability to maintain homeostasis should be assured by provision of exogenous natural antioxidants. People have been converted to phytochemicals as prophylaxis and therefore