A crucial role in osmoregulation against hyperosmotic stress: Carbohydrate and inositol metabolism in Nile tilapia (Oreochromis niloticus)

The purpose of this study was to explore the relationship between inositol metabolism and carbohydrate metabolism in Nile tilapia (Oreochromis niloticus) under acute hyperosmotic stress. 50 mg/mL glucose solution and PBS was injected to the fish of experimental group and the control group, respectively. The fish were then transferred to 16 psu brackish water for hyperosmotic stress immediately, and sampled at 0, 1, 3, 6, 12, 24, and 48 h post stress. The hyperosmotic stress significantly increased the osmotic pressure, glucose content of serum, the process of glycolysis and gluconeogenesis in the liver of fish in both groups over time. The expression of genes involved in myo-inositol (MI) synthesis and transport was all induced by hypertonicity in gill, kidney and liver of fish in both groups. The injection of glucose solution significantly decreased MI synthesis in gill, kidney and liver, and relieved the apoptosis of liver under acute hyperosmotic stress. However, glucose injection significantly increased Na+K+-ATPase activity in the gill, as well as serum osmotic pressure, and the decomposition of carbohydrate, indicating that additional glucose promoted osmoregulation ability of fish. The results of this research suggested that during the hyperosmotic stress, the injection of exogenous glucose could not only provide energy that required for osmoregulation, but also participate in the osmoregulation by acting as an osmolyte itself.

Automated summary

This study aimed to investigate the relationship between inositol metabolism and carbohydrate metabolism in Nile tilapia under acute hyperosmotic stress. Glucose solution and PBS were injected into the experimental and control group fish, respectively, followed by exposing them to brackish water for different time points. The hyperosmotic stress increased osmotic pressure, glucose content, and metabolic processes in the liver of fish. Genes related to inositol synthesis and transport were induced by hypertonicity in gill, kidney, and liver tissues. Glucose injection decreased inositol synthesis and apoptosis in the liver, but increased Na+K+-ATPase activity and osmoregulation ability in the gill.