Fetal and maternal body temperatures measured by radiotelemetry in near-term sheep during thermal stress

Abstract

Using implanted radiotelemeters, we have measured amniotic temperature and fetal lamb and pregnant ewe body temperatures continuously over the last 34 days of gestation and during conditions of thermal stress. Body temperature of the fetus was approximately 0.6 degrees C higher than that of the mother, and the fetomaternal temperature difference remained constant over the last 25 days of gestation, until the immediate prepartum period, when it rose. During exposure to mild heat stress (35 degrees C dry-bulb temperature, 24 degrees C wet-bulb temperature), ewe and fetal body temperatures rose, but fetal temperature rose at a slower rate. Thus the fetomaternal temperature gradient fell significantly in the initial exposure period. In an environment of 4 degrees C, body temperature of the pregnant ewes fell, but the fetomaternal gradient did not change significantly. During maternal fever, heat loss from the fetus was compromised; body temperature of the fetus rose more than that of the mother, and the fetomaternal temperature gradient rose significantly. We suggest that mild heat or cold exposure in pregnant animals constitutes little risk of fetal thermal stress. During maternal fever, however, the fetus may be at risk of thermal injury.

Interleukin-1 receptor antagonist as a modulator of gender differences in the febrile response to lipopolysaccharide in rats

“…Furthermore, we demonstrated that neutralization of endogenous IL-1ra in vivo, using a specific antiserum, results in significantly higher fever responses to LPS in rats (12). The ability of IL-1ra to limit the pyrogenic effects of endogenous IL-1 during infection may be especially important in situations where increases in body temperature could be particularly detrimental, such as to the developing fetus during gestation (4,18,30,42).It is now well documented that febrile responses to infectious agents are significantly attenuated in several mammalian species near term of pregnancy (14,19,25,41,43,69). Although it is tempting to speculate that this may in part be due to the actions of endogenous IL-1ra, little evidence exists to support this to date.…”

“…Furthermore, we demonstrated that neutralization of endogenous IL-1ra in vivo, using a specific antiserum, results in significantly higher fever responses to LPS in rats (12). The ability of IL-1ra to limit the pyrogenic effects of endogenous IL-1 during infection may be especially important in situations where increases in body temperature could be particularly detrimental, such as to the developing fetus during gestation (4,18,30,42).…”

Improved homeothermy and hypothermia in African lions during gestation

“…Over the same period, there was no change in T b of non-pregnant lions. The clear trend of decreasing mean T b in lionesses began in the first trimester (figure 1), earlier than in reports of gestational hypothermia in laboratory animals [7][8][9]. In addition to the decline in mean T b , pregnant lions also regulated T b with greater precision over 24 h, with the mean amplitude of T b 0.68C lower than that when non-pregnant or lactating.…”

“…Gestational hypothermia has been observed in a variety of species under laboratory conditions [7][8][9][10][11], and appears rsbl.royalsocietypublishing.org Biol. Lett.…”

Influence of brain angiotensin on thermoregulation and hydromineral balance during pregnancy in rats

“…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.…”