Maternal Endocrine and Fetal Metabolic Responses to Heat Stress

Abstract

Heat-stressed pregnant ewes deliver intrauterine growth-retarded lambs. Selected maternal and fetal changes were investigated during acute heat stress in order to elucidate the mechanism for this growth retardation. Uterine blood flow decreased 20 to 30% in pregnant ewes during 1 degree C increases in core temperature. The decreases were accompanied by 60 and 100% increases in serum oxytocin and antidiuretic hormone, respectively. These effects were mimicked by salt loading or injections of antidiuretic hormone or oxytocin, suggesting a role for either or both hormones in regulating uterine blood flow during pregnancy. Chronically heat-stressed pregnant ewes were delivered by Caesarean section. Their fetuses were approximately 20% smaller than thermoneutral controls. Within each pair of heat-stressed twins, one fetus weighted one-third less than its litter mate. No difference in weights were observed within the control twins. The livers and brains of the heat-stressed fetuses were disproportionate in size. The livers from the small heat-stressed twins contained only one-half the protein of the controls and one-fourth the protein of their litter mates. Muscle protein was decreased in the heat-stressed fetuses, and liver and muscle glycogen were elevated as were liver arginase, glutamate-pyruvate transaminase and muscle creatinine. These results are consistent with the following hypothesis: heat stress stimulates the release of maternal antidiuretic hormone or oxytocin, which reduces uterine blood flow and causes a shift in fetal metabolism from anabolic to catabolic pathways; one fetus of heat-stressed twins is more severely affected than its litter mate.

Fetal death: comparative aspects in large domestic animals

“…Other environmental factors can also contribute to pregnancy loss. For example, heat stress in sheep has been shown to lead to decreased uterine blood flow and reduced birth weight in lambs (Dreiling et al, 1991). The incidence and types of non-infectious causes of fetal compromise are likely to differ between regions and countries.…”

Whole-body fuel selection: ‘reproduction’

“…In intrauterine growth retardation caused by either fetal crowding or environmental heat stress there is a decrease in uterine blood flow (Dreiling et al 1991;Ferrell & Reynolds, 1992). This leads to a fall in the supply of 0 2 and glucose, and these are general features of fetal growth retardation.…”

Fetal and maternal fluid balance in sheep during hyperthermia with and without water deprivation

“…It has been postulated that the increased uterine blood flow is diverted through arteriovenous shunts which may be responsible for increasing the transfer of heat from the fetus to the mother (Andrianakis & Walker, 1994). Although Oakes et al (1976) and Dreiling & Carman (1991) do not comment about availablity of drinking water in their studies, water was available ad libitum in the study by Andrianakis & Walker (1994).…”

“…When pregnant sheep are heated for 2 h, raising their temperature to 40.5°C, maternal Hct and plasma osmolality are unchanged (Dreiling & Carman, 1991); however, it is not clear whether drinking water was available during the study.…”