Summit metabolism in newborn lambs.

Basal metabolic rate and then summit metabolic rate were measured using a water immersion technique in newborn lambs at 1 h or 4 h old. The mean rates of basal and summit metabolism were 51 +/- 1.5 and 235 +/- 7.9 w per m2 respectively. Summit metabolic rate was more closely related to body surface area than to body weight. Umbilical catheters were inserted at birth and blood samples were taken at 5 min of age and during the measurement of metabolic rate to examine changes in acid-base status and energy substrate concentrations. At birth varying degrees of metabolic acidosis and hyperlactaemia were observed. Summit metabolism was associated with the development of a further metabolic acidosis and with increases in the blood levels of lactate and excess lactate and the plasma levels of glucose, glycerol and free fatty acids. The relationships between summit metabolic rate, the metabolic state at birth and the change in metabolic state caused by cooling suggested that prepartum hypoxia was associated with a depression of the thermogenic response to cold stress and also with a depression of sympathetic nervous activity.