Modulation of acyl and des-acyl ghrelin on autonomic and behavioral thermoregulation in various ambient temperatures.

Maintenance of body temperature (T) at various ambient temperatures (T) during fasting is important for homeotherms. Fasting decreases T in thermoneutral and cold conditions and facilitates thermoregulatory behavior in the cold in rats; however, the mechanism is unknown. We focused on ghrelin, a hormone secreted by the stomach during fasting, in two circulatory forms: acyl ghrelin (AG) and des-acyl ghrelin (DAG). AG is called active ghrelin, while DAG, the non-active ghrelin, was unknown for a long time before its many functions were recently clarified. In the present review, we present the modulation of AG and DAG on autonomic and behavioral thermoregulation at various T and discuss the differences between their modulation on thermoregulation. AG decreases T in thermoneutral and cold conditions but does not affect the thermoregulatory behavior of rodents in cold conditions. The DAG decreases T in thermoneutral and hot conditions, but it does not affect T and facilitates the thermoregulatory behavior of rodents in the cold. These findings indicate that the actions of AG and DAG on thermoregulation are similar in thermoneutral conditions but are different in cold conditions.