Osmotic Stress-induced Gene Expression in the Diencephalon, Kidney, Liver, and Breast Muscle of Chicks.

Endogenous water production is an important response for inducing water acquisition in birds, with proteins and lipids being major sources of endogenous water. However, the roles of protein and lipid metabolism-related gene expression in the regulation of their body fluid balance have not been investigated. This study aimed to clarify the roles of protein and lipid metabolism-related genes in osmoregulation in chicks. In Experiment 1, we examined the effects of 12 h of water deprivation on the mRNA levels of protein and lipid metabolism-related genes and feed intake in chicks. Feed intake was significantly decreased by water deprivation throughout the experimental period. The mRNA levels of vasotocin in the diencephalon were significantly increased by water deprivation. The mRNA levels of carnitine palmitoyltransferase 1A (CPT1A), the rate-limiting enzyme of mitochondrial fatty acid oxidation, were significantly increased by water deprivation in the liver, breast muscle, and diencephalon of the chicks. The mRNA levels of atrogin-1, a regulatory enzyme of the ubiquitin proteasome-system, were significantly increased by water deprivation in the breast muscle of the chicks. In contrast, the mRNA levels of fatty acid synthase, the rate-limiting enzyme of fatty acid synthesis, were significantly decreased by water deprivation in the liver of the chicks. In Experiment 2, the effects of intraperitoneal administration of hypertonic saline were examined under feed and water-deprived conditions. The mRNA levels of renal aquaporin 1, breast muscle atrogin-1, and diencephalon CPT1A were significantly increased 1 h after hypertonic saline injection. These results suggest that osmotic stress may induce protein catabolism in the skeletal muscle and fatty acid catabolism in the diencephalon of the chicks.