Thermal homeostasis in pregnant rats during heat stress.

Abstract

Rats exposed to inescapable heat stress maintained a controlled hyperthermia while increasing heat loss by cutaneous vasodilatation and by grooming behavior. In nonpregnant rats, the evaporation of saliva groomed onto the body surfaces increased exponentially as a function of ambient temperature above 36 °C. In contrast, rats in an advanced stage of pregnancy became dependent on grooming behavior for thermoregulation at ambient temperatures of 30-36 °C. This was associated with a decrease in the body temperature threshold for salivary secretion from the submaxillary gland, which then began at approximately the same body temperature as cutaneous vasodilatation. In addition, the pregnant rats maintained a lower level of controlled hyperthermia during heat stress than did nonpregnant rats. This appeared to result from a decreased production of metabolic heat, reduced insulation on the ventral surface, and an increased motivation to keep cool during heat stress. These changes met the increased need for thermolysis during pregnancy and provided for thermal homeostasis both in the pregnant rat and in the unborn fetuses.Rats exposed to inescapable heat stress maintain a controlled hyperthermia while increasing heat loss by cutaneous vasodilatation and by grooming behavior (see review by . Heat loss by radiation and conduction, primarily from vascularized exposed surfaces such as the tail (Knoppers, 1942;Rand, Burton, & Ing, 1965), is a particularly important avenue of thermolysis in female rats, whose long tails make them less dependent than males on the cooling that results from evaporation of saliva groomed onto the body surfaces (Hainsworth, 1967(Hainsworth, ,1968. During pregnancy, however, their increased girth reduces the relative size of the "thermal window" that is provided by

Physiological and behavioral consequences in rats of water recycling during lactation.

“…However, in contrast to the thermoregulatory control of maternal behavior, which acts to limit or terminate bouts of mother-young contact, the process of fluid exchanges, as described here, serves to maintain or augment contact. Collectively, such studies suggest that, in addition to hormonal and experiential factors, immediate physiological needs may motivate certain maternal behaviors (see also Wilson & Strieker, 1979).…”

Improved homeothermy and hypothermia in African lions during gestation

“…to represent a regulated reduction in T b rather than an inability to regulate a high T b . The threshold temperature for initiating cooling mechanisms was reduced in pregnant compared with non-pregnant rats, indicating that pregnant rats defended a lower T b [12]. Pregnant rats, like nonpregnant rats, also did not select a warmer microclimate when it was made available to them [7].…”

System-level Insights into the Adaptation of Domestic Dairy Buffalo to Chronic Heat Stress

“…LL-37 and acetylcholine were mapped to the salivary secretion pathway. As buffalo, which have few sweat glands [3], dissipate only 12% of their excess heat through skin evaporation [9]; salivary secretions have been shown to help decrease body temperature [62,63].…”