High Dietary Zinc Promotes its Optimal Absorption Through Modulation of Key Transporter Genes, SOD1, and HSP70 Expression in Heat-stressed Rats.

Global warming causes heat stress (HS) in animals, impacting nutrient absorption and metabolism. Antioxidant nutrients are crucial for combating HS. This study assessed the impact of increased dietary Zn on nutrient utilization, mineral absorption, and expression of Zn homeostasis regulators, superoxide dismutase-1 (SOD1), and heat shock protein-70 (HSP70) genes in rats under HS. Seventy-two four-week-old Wistar rats were assigned to six groups in a 3×2 factorial design, with three dietary Zn levels (14.6, 32.7, and 48.9 ppm) and two environments, thermo-neutral (TN) and HS, for 42 days, including 14 days of HS exposure. Results showed that HS reduced nutrient intake across Zn levels, though ether extract digestibility increased at 32.7 and 48.9 ppm Zn. Intake, excretion, and apparent daily absorption of Ca, P, Zn, Cu, Mn, and Fe were lower in HS than in TN groups. Hepatic metallothionein-1 (MT1) mRNA expression was downregulated in rats fed 14.6 and 32.7 ppm Zn compared to 48.9 ppm Zn under both environmental conditions. Duodenal Zinc transporter-1 (ZnT1) and Zrt- and Irt-like protein-1 (ZIP1) mRNA expression increased with dietary Zn under TN and HS conditions, respectively. Hepatic SOD1 mRNA expression was significantly downregulated in HS groups, while hepatic HSP70 mRNA expression was significantly upregulated at 48.9 ppm Zn under HS. Present study suggests that, under HS conditions in rats, a higher dietary Zn level of 48.9 ppm may be optimal for improving Zn absorption, enhancing ZIP1, MT1, and HSP70 gene expression, and alleviating the negative effects of HS.