L-Citrulline Influences the Body Temperature, Heat Shock Response and Nitric Oxide Regeneration of Broilers Under Thermoneutral and Heat Stress Condition

Abstract

Heat stress (HS) adversely affects several physiological responses in organisms, but the underlying molecular mechanisms involved are yet to be fully understood. L-Citrulline (L-Cit) is a nutraceutical amino acid that is gaining research interest for its role in body temperature regulation and nitric oxide synthesis. This study investigated whether dietary supplementation with L-Cit (1% of basal diet) could ameliorate the effects of acute HS on thermotolerance, redox balance, and inflammatory responses of broilers. Ross 308 broilers (288 chicks) were subjected to two environments; thermoneutral at 24°C (TNZ) or HS at 35°C for 5 h, and fed two diets; control or L-Cit. The results showed that HS increased the ear, rectal (RT), and core body (CBT) temperatures of broilers, along with higher respiratory rate. The RT and CBT readings were intermittently affected with time effect, whereas, L-Cit supplementation lowered the mean CBT than the control diet. Antioxidant assays showed that superoxide dismutase was increased during HS, while, catalase was promoted by L-Cit supplementation. In addition, L-Cit induced glutathione peroxidase activity compared to the control diet during HS. Hypothalamic heat shock protein (HSP)-90 was upregulated by HS, but L-Cit downregulated heat shock factor (HSF)-1, and HSP 60 mRNA expressions. HSF 3 mRNA expression was downregulated by L-Cit under TNZ condition. More so, HS increased the plasma nitric oxide (NO) concentration but lowered the total NO synthase (tNOS) activity. In contrast, L-Cit supplementation limited NO production but increased the tNOS activity. Arginase activity was increased in the control fed group during HS but L-Cit supplementation lowered this effect. The NOS-COX pathway was significantly affected under TNZ condition, since L-Cit supplementation downregulated the mRNA expression of iNOS-COX2 in the hypothalamus, and further reduced the serum PGE2 concentration. Together, these data indicates that L-Cit influenced the antioxidant defense, heat shock response and nitric oxide regeneration both under thermoneutral and HS conditions; and that L-Cit may be directly and/or indirectly involved in the central regulation of body temperature.

Research Note: Effects of dietary L-arginine on the production performance and gene expression of reproductive hormones in laying hens fed low crude protein diets

“…The NO concentration in serum was detected using a commercial kit (Jiancheng Bioengineering Institute, Nanjing, Jiangsu, China), as previously reported ( Uyanga et al., 2021 ). The absorbance was detected at 540 nm using a microplate reader (Elx808, Bio-Tek Winooski, VT).…”

Potential Implications of Citrulline and Quercetin on Gut Functioning of Monogastric Animals and Humans: A Comprehensive Review

“…Impairment in citrulline availability and de novo arginine synthesis reduced NO production but was restored with citrulline supplementation [159]. Thus, citrulline is implicated in the regulation of NO production for homeostasis, as against NO overproduction and toxicity [160].…”

“…Under oxidative stress conditions, citrulline and quercetin would be useful in combating ROS and altering the redox status of the gut. Citrulline has been widely known for its antioxidant properties, which has been attributed either to the direct effects of citrulline and/or indirect effects via NO production [160,172]. Citrulline directly mediated antioxidant defense by influencing the enzyme activities of catalase, superoxide dismutase (SOD), and the total antioxidant capacity, but decreased MDA contents, abolishing the degree of lipid peroxidation [43].…”

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

“…The ability of Arg to reduce physiological stress is likely to be attributed to its antioxidative effects ( Gupta et al, 2005 ). Arg is also the only nitrogen donor in the production of nitric oxide, which is involved in vasodilatation to potentially aid thermoregulation of heat-stressed birds ( Uyanga et al, 2021 ). Interestingly, more focus is being placed on the potential beneficial effects of citrulline (Cit), a compound synthetized during Arg catabolism and the formation of nitric oxide.…”

“…Recent studies have shown that Cit supplementation can effectively increase systemic Arg levels, even more than direct L-Arg supplementation ( Morita et al, 2014 ; Agarwal et al, 2017 ). Cit concentration in blood has also been shown to be modulated by hot temperatures ( Chowdhury et al, 2014 ; Chowdhury, 2019 ) and its supplementation may increase nitric oxide synthesis, provide an anti-inflammatory response, and enhance the central regulation of body temperature ( Chowdhury et al, 2017 ; Uyanga et al, 2021 , 2022 ).…”