Effect of delivery temperature on endocrine stimulation of thermoregulation in lambs born by cesarean section.

Abstract

We examined the hypothesis that exogenous stimulation with physiological doses of 3,5,3'-triiodothyronine (T(3)) and/or norepinephrine at birth can improve thermoregulation in near-term lambs delivered by cesarean section. This was achieved by investigating the effect of delivery temperature [i.e., warm (30( degrees )C) vs. cool (15( degrees )C) ambient temperatures] on hormonal stimulation on uncoupling protein-1 (UCP1) abundance in brown adipose tissue. In vivo measurements of temperature control (i. e., colonic temperature, oxygen consumption, and incidence of shivering) were made over the first 2.5 h after birth. Each lamb was injected with saline with or without T(3), norepinephrine, or T(3) plus norepinephrine. Irrespective of delivery temperature, abundance of UCP1 increased and incidence of shivering decreased by all hormonal treatments, but this only reduced the rate of decline in colonic temperature of cool-delivered lambs. Oxygen consumption was higher in cool-delivered lambs that were able to fully restore body temperature, an adaptation not observed in controls or any warm-delivered groups. Exogenous administration of endocrine stimulatory factors can enhance the abundance of UCP1 in cesarean-section-delivered lambs with the magnitude of thermoregulatory response being greater at cool than warm delivery temperatures.