INFLUENCE OF PERIOD LENGTH OF LIGHT-DARK CYCLES ON THE BODY-WEIGHT AND FOOD-INTAKE OF YOUNG-RATS

The purpose of this work is to test whether physiological factors, suc h as body weight or food intake, are related to the period of environm ental cycles under which animals are kept. We studied body weight incr ease, daily food intake and efficiency (i.e. relationship between body weight increase and food intake) of 7 groups each containing 20-24 ma le rats. Measurements were recorded every 4 days from the day of weani ng (25 days old) during 64 days. Each group of rats was kept under a s ymmetrical LD cycle. The period of the cycles studied were: 22, 23, 24 , 25, 26, 27 and 28 hours (T22, T23...T28). Results show differences i n the three variables studied for groups T25 and T26. These animals sh ow an inferior body weight, less food intake and less efficiency. It w ould seem that the difference between the period of the external LD cy cle and the endogenous period of the animals rhythm induces changes in the energetic needs of the organism.