This study was designed to determine whether or not a number of diverse rhythmic variables in the rat could be synchronized to meal timing. This was tested by restricting the availability of food; once during each 24-hour period an unrestricted quantity of food was made available for a 4-hour period to four different groups at different phases of the light-dark cycle, and the rhythms of the variables studied in the different groups were compared. Liver glycogen and serum glucose did synchronize to or were strongly influenced by feeding schedules; corticosterone and the several enzymes measured seemed to reflect an interaction of both the restricted feeding schedule and the light-dark cycle. The mitotic index in the corneal epithelium in all groups remained remarkably synchronized to the light-dark cycle and was altered only minimally by restricted meal timing. All groups on restricted feeding schedules gained less weight than the group fed ad libitum and maintained on a light-dark cycle. These studies caution against assuming that all body functions react in the same manner to different synchronizers; and they emphasize that one must not generalize about the synchronizing effect of meal-timing or even the light-dark cycle.

No abstract

The so-called "normal values" reported for noradrenaline and adrenaline in blood plasma of man vary in a wide range which is mainly ascribed to technical factors, external stimuli as weil as inter-individual differences (Callingham 1975). The influences of circadian variations of cateeholamines in blood of healthy individuals have not been studied systematically whereas circadian variations in the urinary excretion of catecholamines and their metabolites are weil described (e.g. This paper deseribes a 24-hr study of plasma concentrations of noradrenaline and adrenaline in 81 young presumably healthy yolunteers (soldiers), subjected to a regulated life: unstrenuous body exercise on the day of assay and during the 3 previous days; fixed times of meals and rest: breakfast 06.15, luneh 12.30, dinner 18.15 (a standard military menu); sleep 22.00-05.00. From a group of 25 individuals blood sampies were obtained by collecting 20 ml blood by venepuneture at 4-hourly intervals during an uninterrupted 24-hr period, from 06.00 until 06.00 hr the following day (= serial dependent sampling). Besides, from 7 groups of 8 volunteers each, blood was withdrawn only once during the 24-hr per iod at different times (= serial independent sampling). The blood was taken during a short interruption of the normal work of the individuals, always before food intake. Great care was taken to minimize the disturbance of the subjeets while sleeping. The concentrations of the catecholamines in the blood plasma were determined fluorometrically by the method of Anton and Sayre 0962). The results were statistically tested by the Student's t-test and the analysis of variance (F-test). Furthermore, the eorrelation coefficient (re) of the rhythmic variables of both groups was calculated. Two main results have been obtained: 1) Both eatecholamines exhibit circadian fluctuations. 2) The 24-hr mean values and the circadian pattern depend on the mode of sampling.Adrenaline (Fig.

157Despite of the clinical interest in serotonin (5-HT) levels in blood very little is known about its 24 hour (= circadian) fluctuation. In literature only 5 healthy persons and 11 mentally retarded patients (Ha/berg, Anderson, Ertel and Berendes 1967) and 13 healthy young men (Kanabrocki, Scheving, Halberg, Brewer and Bird 1974) were investigated in this respect. We studied the blood from 64 soldiers who volunteered for this study. These persons were on the day of the assay and during the 3 previous days subjected to a very regulated life: unstrenous exercises, and precise eating and sleeping hours: breakfast 06.15, lunch 12.30, dinner 18.15 (military standard food); sleep 22.00-05.30.