EFFECT OF DIFFERENT AMBIENT-TEMPERATURE AND LIPOPOLYSACCHARIDE ADMINISTRATION ON THE CIRCADIAN-RHYTHM OF RECTAL TEMPERATURE AND HYPOTHALAMIC PGE, PRODUCTION IN AGED MALE-RATS

Old and young male rats (22 and 7 months respectively) were exposed to ambient temperatures of 4 22, 27 and 35 degrees C. The rats' rectal t emperatures (RTs) were measured periodically, after exposure to the va rying temperatures at different hours during the day. The mean circadi an value of RTs in the aged rats was different from that of the young rats. Whereas exposure to low temperatures caused a decrease of 2.0 de grees in the RTs of the old rats, exposure to heat (35 degrees C) caus ed an increase of 1 degrees C in their RTs. An injection of 200 mu g ( intraperitoneally) of E. coil lipopolysaccharide caused them to experi ence a long period of hypothermia. Elevation in the RTs after the hypo thermic period ended was significantly lower in the old rats. However no significant differences in hypothalamic PGE, production were to be found between the old and young groups 24 h after pyrogen administrati on.