Differences in circadian time course and level for the plasma concentrations of glucose, free fatty acids and amino acids between ad lib‐eating and fasting rabbits

Abstract

The entrained rhythm in food approaches, representative of the circadian fluctuation in locomotor and food intake activity was recorded from 12 rabbits eating ad libitum during exposure to an LD 12:12 h-regimen. They were also subjected to 53 h-sessions with the same LD alternation, in which blood samples were taken at 2 h-intervals. During these sessions 6 of them were permitted to eat freely whereas the others were food-deprived. It appeared that in eating rabbits plasma levels are higher for glucose and a-amino nitrogen but lower for free fatty acids and, further, that eating specimens exhibit marked circadian fluctuations in the levels of glucose and FFA which are closely correlated with, and probably a consequence of, the circadian rhythm in the amounts of food actually taken up in the course of the sessions. In fasting rabbits, however, the same plasma parameters show rhythms with quite another time course, that can be attributed to the circadian fluctuations in (locomotor) activity and endocrine balance.

Re‐entrainment of the Rabbit's circadian food intake pattern after inversion of 24‐hr sawtooth illuminations and standard light‐dark alternations

“…It is highly improbable that this linear change of the illumination intensity over 24 hours would in itself have an entraining action, because the circadian system responds in a logarithmic way to the illumination level of photic pulses (Meijer et al, 1986) Care was taken as much possible to ensure that switching-over from one photic schedule to another {i.e., inversion or conversion) was effected without a hitch, although occasionally an intermediate period of 24 Recording and data analysis The 10 food hoppers were each provided with a flap actuating a switch-contact on being pushed outwards. In this way the number of food approaches, representative of food uptake by rabbits (Bobbert et al, 1989), was recorded from each animal for the consecutive 30-min intervals (DEC, LSI -11) of continuous recording over more than 1.5 years. With midnight winter time (w.t.)…”