DIFFERENCES IN SLEEP VARIABLES, BLOOD ADENOSINE, AND BODY-TEMPERATUREBETWEEN HYPOTHYROID AND EUTHYROID RATS BEFORE AND AFTER REM-SLEEP DEPRIVATION

Sleep deprivation causes an increase in energy expenditure in animals. Thyroid gland function has been related to metabolic function. and th is may be compromised in sleep manipulations. The objectives of the pr esent study were the following: 1) to develop a model of hypothyroid r ats by surgical removal of thyroid glands without extirpation of the p arathyroid; 2) to observe the sleep architecture in euthyroid (Etx) an d hypothyroid (Htx) rats, both before and after rapid eye movement (RE M) sleep deprivation (96 hours); 3) to challenge both groups (i.e. Err and Htx) with REM sleep deprivation (96 hours) and then evaluate the effects on temperature; and 4) to measure the levels of adenosine and thyroid hormones in blood. One-month-old Wistar male rats (weight 90-1 00 g) were studied. The thyroid gland was removed, and the parathyroid glands were reimplanted within the neck muscle (Htx) under halothane anesthesia. A sham-operated group was also included (Err). Four months later, the animals were studied according to the following protocols. Protocol 1: Animals of both groups (i.e. Etx and Htx) were implanted for sleep recordings. After a baseline polysomnography, these animals were REM sleep deprived by the platform method (96 hours). Protocol 2. An intraperitoneal temperature transducer was placed into animals of both groups under deep halothane anesthesia. They were studied at base line, during 96 hours of REM sleep deprivation, and on the rebound per iod. Protocol 3: Plasma thyroid hormones [T3, T4, and thyroid-stimulat ing hormone (TSH)] and plasma adenosine were determined in both groups . Results of protocol 1 indicated that the main difference observed in Htx rats during the baseline sleep was an increase in delta sleep (sl ow-wave sleep 2) and a reduction in waking time compared with Err anim als. REM sleep rebound after 96 hours of REM sleep deprivation was sim ilar in both groups. In protocol 2, the main finding was that Htx anim als had reduced body temperature. A significant difference in body tem perature between Etx and Htx animals was found mainly during lights-on period. REM sleep deprivation in the Etx group produced an increase i n body temperature. Htx animals showed the opposite effect, with a red uction in body temperature during and after REM sleep deprivation. In protocol 3, the main findings were that Htx animals exhibited a signif icant reduction in blood thyroid hormones (T3, T4), and that they also had high levels of plasma adenosine. REM sleep deprivation produces c hanges in temperature regulation. The increase in body temperature dur ing REM sleep deprivation may require thyroid integrity. Absence of th e thyroid gland does not seem to influence REM sleep recovery after it s deprivation. The high plasma adenosine levels found in the Htx group may explain the increase in delta sleep in this group.