Estrous cycle variations of food and water intake in rats in the heat

Effects of heat and estrous cycle on food and water intake and on the kinetics of water metabolism were studied in Holtzmann rats, 12 adult females per group. The animals were housed individually in metabolic cages, in series, in a controlled-environment room at (24.5 degrees C) followed by two experimental temperatures (29.2 degrees C and 34.0 degrees C). In all cases relative humidity was 50% and the photoperiod 12L:12D (L = 0600--1800 h). Intake of food and water, available ad libitum, were measured and recorded daily for at least five consecutive estrous cycle (about 25 days). Water turnover was measured using tritiated water. The results indicate that the experimental conditions constituted stressful environments for the rats. Their corticosterone levels were significantly (P less than 0.01) elevated and a relative lymphopenia and neutrophilia (P less than 0.01) were observed. Additionally, food intake was decreased and water intake increased, both significantly (P less than 0.01). Body water turnover was increased (P less than 0.01) while body water pool size and the biological half-life for 3H2O were reduced. However, the cyclic variation of food and water intake and its relationhsip to the estrous cycle were unchanged.