Effect of Vasopressin on Circadian Heart Rate, Body Temperature, and Activity

Abstract

Male, vasopressin-containing, Long-Evans (LE) and vasopressin-deficient, Brattleboro (DI) rats were maintained in individual cages while telemetered heart rate (HR), core body temperature (BT) and activity level (AC) data were collected. The rats were exposed to a 12:12 light-dark cycle with room temperature maintained at 23±1°C. A 1h feeding period was initiated 1h after the beginning of the dark cycle and another 1h feeding period commenced 7h into the dark cycle. While patterns of circadian rhythms of HR, BT, and AC were similar between DI and LE rats, there were significant differences in all three variables. When compared to LE animals, DI animals had a significantly: 1) slower HR throughout the circadian cycle; 2) lower BT throughout most of the circadian cycle; and 3) higher AC levels at the onset of the dark cycle. Results show that vasopressin plays a modulatory role in circadian rhythms of HR, BT, and AC.