INFLUENCE OF MATERNAL DEXAMETHASONE ADMINISTRATION ON THERMOREGULATION IN LAMBS DELIVERED BY CESAREAN-SECTION

We have previously shown that lambs delivered by caesarean section 1 w eek prematurely become hypothermic due to reduced brown adipose tissue function in conjunction with low plasma concentrations of cortisol an d thyroid hormones. The present study therefore aimed to determine whe ther maternal dexamethasone (a synthetic corticosteroid) administratio n could improve thermoregulation in premature lambs to the extent that they become similar to term lambs. Lambs were either delivered by cae sarean section into a warm (30 degrees C; WD) or cool (15 degrees C; C D) ambient temperature at 140 days of gestation, 2 days alter maternal dexamethasone treatment, or at 146 days for controls. During the firs t 30 min of life the decline in colonic temperature was greater in dex amethasone treated lambs compared with controls delivered into the sam e ambient temperature. All lambs then restored colonic temperature alt hough this adaptation took longest in dexamethasone treated lambs CD b ut these subsequently attained highest plateau colonic temperatures. O xygen consumption, breathing frequency and plasma free fatty acid conc entrations 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 lamb s, uncoupling protein content was higher in lambs CD compared with tho se WD. An effect of ambient temperature on thermogenic activity was on ly observed in the dexamethasone treated group. It is concluded that m aternal dexamethasone treatment can significantly improve thermoregula tion after birth following premature delivery by caesarean section. As a consequence, dexamethasone treated lambs delivered 1 week premature ly do not remain hypothermic and have higher or similar colonic temper atures compared with untreated lambs born 1-2 days before term.