The effects of chronic cold exposure on diurnal corticosterone and aldosterone rhythms in Sprague-Dawley rats

Plasma corticosterone (CORT) and aldosterone (ALDO) exhibit diurnal rhythmicity. Cold exposure increases basal plasma CORT and ALDO levels. This study investigated the effects of cold exposure on CORT and ALDO diurnal rhythms. Twelve male Sprague-Dawley rats were housed at 23°C, adapted to a 12:12 day:night cycle (lights on 0900 h), and provided chow and water ad lib. On day 7, 100 μl tail blood samples were obtained every 4 h for 24 h beginning at 0900 h. The temperature of the animal room was lowered to 4°C. On days 7 and 14 of cold exposure, blood samples were obtained every 4 h as above. After 7 days at 4°C, CORT levels were elevated at 0900 h, 1300 h, and 0500 h ( p < 0.05) as compared to levels observed at 23°C. Peak CORT levels were observed at 2100 h in each 24-h sampling session with mean levels of 181.3 ± 23.3 ng/ml at 23°C, and 200.5 ± 16.4 ng/ml and 188.1 ± 19.9 ng/ml after 7 and 14 days at 4°C. In contrast, ALDO levels were elevated at all time points across the day:night cycle after 7 days at 4°C. After 14 days, ALDO levels were elevated at 0900 h, 1300 h, and 2100 h ( p < 0.05) as compared to levels observed at 23°C. Peak ALDO levels occurred at 2100 h in each 24-h sampling session with mean levels of 199.9 ± 24.4 pg/ml at 23°C, and 361.4 ± 18.2 pg/ml and 342.1 ± 31.6 pg/ml after 7 and 14 days at 4°C. Cold exposure initially elevated CORT and ALDO levels possibly by reducing the effectiveness of negative feedback of CORT on the hypothalamic-pituitary-adrenal axis. However, ALDO levels remained elevated after 14 days at 4°C while CORT levels returned to baseline, suggesting different regulatory mechanisms after prolonged cold exposure.