The effect of dietary phosphorus on heat shock protein mRNAs during acute heat stress in male broiler chickens ( Gallus gallus)

Abstract

A 2×2 factorially arranged completely randomized experimental design was used to study the relationship between inorganic phosphorus (P i) and heat shock protein (HSP) mRNA expression in different organs of commercial broiler cockerels during acute heat stress (HS). Brain, heart, liver and spleen were assayed for hsp70, hsp90α and hsp90β mRNA. At 1 day of age, chickens were assigned randomly to two dietary P i treatment groups (P i−: 0.16%; P i+: 0.5%). At 3 weeks of age, half of the chickens in each P i group were subjected to HS ( T a=41 °C, 60 min) while the other half was maintained in a thermoneutral environment (CN, T a=25 °C). The results showed inter-organ variation in the expression of HSP mRNAs. Brain expressed the most HSP mRNAs while spleen expressed the least. When broilers were subjected to HS, the expression of HSP mRNAs was influenced positively by the consumption of the P i+ diet. However, analysis of variance revealed that T a influenced HSP transcription more than phosphorus availability. Thermal stress caused induction of hsp90α and hsp90β in heart, liver and spleen, but hsp90α and hsp9β mRNA levels were stable in brain. Transcription of hsp70 increased ( P≤0.05) in all organs from chickens in HS groups when compared to chickens in CN groups. Although P i+ did not show any significant increases in the expression of hsp mRNAs, there were consistently larger HSP mRNA values in liver and spleen tissues. The high expression of hsp90α and hsp90β in brain of chicks in both CN and HS conditions could be due to the involvement of hsp90 in steroid hormone receptors or the high metabolic activity of neurons in the central nervous system.