Diurnal changes in plasma glucose and insulin responses to oral glucose load in rats

The plasma glucose and insulin responses to an oral load of glucose were examined in the daytime and at night in unanesthetized and unrestrained rats. In rats that had been fed during the nighttime (2200-0400 h) every day for 2 wk, the plasma glucose and insulin responses were significantly greater (P less than 0.05) at night (2200-2400 h) than in the daytime (1000-1200 h). In rats that had been fed during the daytime (1000-1600 h), the plasma glucose and insulin responses were greater in the daytime than at night (P less than 0.05). It was concluded that the diurnal variations in the plasma glucose and insulin responses to an oral glucose load are closely related to the feeding schedule on which the rats are kept.