Influence of maternal dexamethasone administration on thermoregulation in lambs delivered by caesarean section

Abstract

We have previously shown that lambs delivered by caesarean section 1 week prematurely become hypothermic due to reduced brown adipose tissue function in conjunction with low plasma concentrations of cortisol and thyroid hormones. The present study therefore aimed to determine whether maternal dexamethasone (a synthetic corticosteroid) administration could improve thermoregulation in premature lambs to the extent that they become similar to term lambs. Lambs were either delivered by caesarean section into a warm (30 C; WD) or cool (15 C; CD) ambient temperature at 140 days of gestation, 2 days after maternal dexamethasone treatment, or at 146 days for controls. During the first 30 min of life the decline in colonic temperature was greater in dexamethasone treated lambs compared with controls delivered into the same ambient temperature. All lambs then restored colonic temperature although this adaptation took longest in dexamethasone treated lambs CD but these subsequently attained highest plateau colonic temperatures. Oxygen consumption, breathing frequency and plasma free fatty acid concentrations were highest in dexamethasone treated lambs CD. There were no differences in plasma thyroid hormones between groups, but cortisol concentrations were lower in dexamethasone treated lambs irrespective of delivery temperature. Analysis of brown adipose tissue samples at 6 h of life demonstrated that dexamethasone treated lambs WD had more uncoupling protein and, in both dexamethasone treated and control lambs, uncoupling protein content was higher in lambs CD compared with those WD. An effect of ambient temperature on thermogenic activity was only observed in the dexamethasone treated group. It is concluded that maternal dexamethasone treatment can significantly improve thermoregulation after birth following premature delivery by caesarean section. As a consequence, dexamethasone treated lambs delivered 1 week prematurely do not remain hypothermic and have higher or similar colonic temperatures compared with untreated lambs born 1-2 days before term.

Ambient Temperature, Maternal Dexamethasone, and Postnatal Ontogeny of Leptin in the Neonatal Lamb

“…The effect of delivery temperature on leptin mRNA was not apparent in lambs born to ewes that had been administered with dexamethasone for 2 d before delivery. Dexamethasone promotes maturation of brown adipose tissue to the extent that lambs born 1 week prematurely are better able to effectively thermoregulate and have more UCP1 (14). Clinical studies have demonstrated plasma leptin to be increased 3-fold after maternal steroid treatment (13), although whether this was because of a change in leptin secretion by the placenta or fetal adipose tissue has not been established.…”

“…The lack of a reduction in leptin mRNA in cool-delivered dexamethasone-treated lambs may be indicative of increased mRNA stability (24) and override any peripheral signals, such as increased catecholamines, which would normally inhibit leptin secretion (25). These temperature-related differences in leptin mRNA abundance could have contributed to the improved thermoregulation after cesarean section birth into a cool ambient temperature (14). To this extent, an acute increase in plasma leptin improves the ability of neonates to maintain colonic temperature (26).…”

“…Plasma concentrations of cortisol were measured by ELISA as described by Clarke et al (14). Leptin was determined using a validated double antibody RIA as described by Delavaud et al (19).…”

“…The parallel increase in leptin (5) and UCP1 mRNA (11) with increasing gestation occurs at the same time that fetal cortisol production is rising (12). Maternal antenatal steroid treatment increases neonatal plasma leptin (13) and UCP1 function (14), but effects on leptin mRNA have not yet been determined. The newborn's ability to thermoregulate is enhanced by maternal dexamethasone administration, and the magnitude of response is influenced by delivery temperature (14).…”

“…Maternal antenatal steroid treatment increases neonatal plasma leptin (13) and UCP1 function (14), but effects on leptin mRNA have not yet been determined. The newborn's ability to thermoregulate is enhanced by maternal dexamethasone administration, and the magnitude of response is influenced by delivery temperature (14). It is not known, however, whether route of delivery and ambient temperature influence leptin status in the newborn.…”