INFLUENCE OF ROUTE OF DELIVERY AND AMBIENT-TEMPERATURE ON THERMOREGULATION IN NEWBORN LAMBS

We examined the effect of route of delivery on brown adipose tissue (B AT) function and thermoregulation in lambs born either vaginally at te rm or by cesarean section close to term. Immediately after birth, lamb s were placed in a warm (30 degrees C; WD) or cool (15 degrees C; CD) ambient temperature, and measurements of colonic temperature, plus hea t production (i.e., oxygen consumption and carbon dioxide production), were recorded for 6 h. Over the first 30 min of life, colonic tempera ture remained constant in vaginally delivered lambs and was lower in t he WD group. Following cesarean section delivery, colonic temperature declined rapidly, a response that was greater in the CD group. Cesarea n section-delivered lambs had an increased reliance on shivering therm ogenesis and restored colonic temperature after 2 h, and by 6 h these parameters were higher than in lambs born vaginally. Irrespective of d elivery, temperature, plasma thyroid hormone concentrations and norepi nephrine content of BAT were lower in lambs born by cesarean section c ompared with those born vaginally. Plasma cortisol concentrations and epinephrine content of BAT were greater in lambs born by cesarean sect ion. The amount of uncoupling protein suid level of guanosine 5'-dipho sphate binding in BAT were higher in vaginally delivered than in cesar ean section-delivered lambs, and for each group mean values were great er for CD than WD lambs. Cesarean section delivery results in altered thyroidal, adrenal, and sympathetic activity, which appears to have a marked influence on BAT function, thereby contributing to distinct dif ferences in thermoregulation compared with lambs born vaginally.