Time-dependent changes in body temperature rhythm induced in rats by brewer's yeast injection.

The aim of the present work was to document the possible influence of the time of administration of brewer's yeast on a model of fever previously reported. Forty male Wistar AF IOPS rats were recorded every hour for 24 h; 2 days later, five groups (four animals each) were injected subcutaneously (neck) at 09:00 or 20:00 h with four different doses of brewer's yeast (group A, 2.5 g/kg; group B, 2 g/kg; group C, 1.5 g/kg; group D, 1 g/kg) or with the equivalent volume of saline (group E, controls). Rectal temperature was recorded every hour for 24 h with an electronic thermometer with a thermistor probe inserted rectally. All data were quantified (means +/- SEM) and compared by analysis of variance (two ways). The circadian variations of temperature were assessed by cosinor analysis. Brewer's yeast-induced fever was statistically significant since increases of 01.04 to 0.77 degrees C and of 0.47 to 0.73 degrees C were observed compared with matched controls after the morning and the evening administration, respectively. A significant circadian rhythm of temperature was detected (p < 0.001) in controls before and during the experiments and in the differently treated groups. The effect of brewer's yeast was different according to the hour of its administration: after morning injection, the mesor of the circadian rhythm was significantly increased as compared with controls and the acrophase was significantly shifted in proportion to the dose. Concerning the evening dosing, the amplitude and the mesor of the circadian rhythm were increased and the acrophase was significantly shifted. During the 4 h following injection, brewer's yeast may induce hyper- or hypothermia.(ABSTRACT TRUNCATED AT 250 WORDS)