Food deprivation induced parallel changes in blood glucose, plasma free fatty acids and feeding during two parts of the diurnal cycle in rats.

The changes in plasma glucose and free fatty acid levels and in subsequent feeding induced by 4 to 10 hr of food deprivation were investigated in rats and compared for the two parts of the diurnal cycle. It was found that increasing fast duration at night induced a more rapid fall of plasma glucose and elevation of plasma free fatty acids than in the day. However, a similar increment of the first post fast meal was elicited by an identical decrement of blood glucose level for the two periods except after a 10 hr fast during the day. The acute effect of darkness and light per se being experimentally excluded, it was concluded that the size of the first meal following short term food deprivation was dependent throughout the diurnal cycle on the fast induced glucoprivic condition.