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. Influence of brain angiotensin on thermoregulation and hydromineral balance during pregnancy in rats. J Appl Physiol 98: 1813-1819, 2005. First published December 3, 2004 doi:10.1152/japplphysiol.00842.2004.-During mammalian pregnancy, body temperature decreases and there are changes in fluid and electrolyte balance. Angiotensin signaling mechanisms in the brain have been shown to influence thermoregulation and body fluid balance in the nonpregnant state. We hypothesized that brain angiotensin is also implicated in adjusting these physiological systems in the pregnant rat. We compared core temperature and fluid regulation in three groups of pregnant rats: untreated rats, rats receiving continuous infusion of an AT1 antagonist candesartan (5 g ⅐ kg Ϫ1 ⅐ day Ϫ1 ) into a lateral cerebral ventricle to block brain AT1 receptors, and rats receiving vehicle [artificial cerebrospinal fluid (aCSF)] vehicle. Untreated and aCSF-treated rats showed a decrease in colonic temperature (Ϫ0.5 and Ϫ0.8°C respectively) by day 20 of gestation. However, rats treated with candesartan had increased colonic temperature compared with baseline (ϩ0.9°C), and their temperature was significantly higher on days 7 (P Ͻ 0.05), 17 (P Ͻ 0.05), and 20 (P Ͻ 0.001) compared with the other groups (aCSF and untreated). Daily food and water intakes and body weight were not different between the three groups. Similarly, litter sizes and pup weights were equal in all groups. Finally, the expected decreases in plasma Na ϩ and osmolality during pregnancy were equivalent in all groups. This study suggests that brain angiotensin mediates the progressive decrease in body temperature that occurs during pregnancy. However, the changes in fluid balance associated with pregnancy are not dependent on brain angiotensin. gestational hypothermia; candesartan; osmoregulation; lactation DURING PREGNANCY, REVERSIBLE changes occur in maternal homeostasis that alter body weight, temperature, and hydromineral balance (25). In several mammalian species that have been investigated, there is a 0.5-1°C reduction in maternal temperature toward the end of pregnancy (13,19,26). In late-pregnant rats studied in a thermocline (temperature gradient between 12 and 36°C), environmental temperature preference was unchanged between pregnant and nonpregnant animals (12), indicating that the reduction in maternal temperature is under thermoregulatory control rather than an inability to maintain a higher temperature. Similarly, the threshold temperature for cooling mechanisms such as skin vasodilation and salivary evaporative heat loss are reduced compared with nonpregnant rats (32), indicating that pregnant rats defend a lower body temperature. Fetal temperature in sheep has been shown to be higher than maternal temperature, which may indicate that the mother functions as a heat sink for its offspring to maintain optimal physiological temperature in utero (19). This reduction has been proposed to be both a neuroprotective mechanism against induction of hyperthermic stress in developing...