Catecholamine-induced Lipolysis and Its Relation to Oxygen Consumption in the Newborn Piglet

Abstract

Extract The relation between changes in oxygen consumption (VO2) (in milliliters per kilogram and minute) and changes in levels of free fatty acids (FFA) and glycerol in plasma, lactate, pyruvate, and glucose levels in blood, and skin and rectal temperatures following norepinephrine or epinephrine infusions has been studied in neonatal piglets who lack brown fat and rapidly increase their body fat content after birth. Fourteen animals, age 17 hr-13 days (Table IA), each received two 25-min infusions of 2.0 μg/kg.min of norepinephrine (see Fig. 3); nicotinic acid (50 mg/kg) was administered prior to the second infusion. Five animals, age 5 hr-11 days (Table IB), each received two infusions of 0.2–4.0 μg/kg.min of epinephrine (Fig. 5). The elevated levels of glucose in blood, and FFA and glycerol concentrations in plasma observed following norepinephrine infusions correlated with postnatal age and body weight, suggesting that the magnitude of the norepinephrine-induced lipid mobilization was dependent upon body fat content. There was no definite tendency for VO2 responses to norepinephrine to increase with increasing postnatal age (Table IA). The increases in glycerol levels (Fig. 2) and FFA (Fig. 1) concentrations occurring after norepinephrine stimulation were suppressible by nicotinic acid. The increases in VO2 occurring after norepinephrine infusion (Table IA) were small (mean of 0.85 and 0.57 ml/kg.min during infusion prior to and following nicotinic acid administration, respectively) and variable and did not appear to be accentuated by previous starvation for 48 hr; they were related neither to elevations of any of the biochemical variables monitored nor to the small increases in skin and rectal temperatures observed. The changes in VO2 after epinephrine infusions (Table IB) were quantitatively similar to those recorded during norepinephrine infusions and were not correlated to changes in concentrations of glucose, plasma FFA or glycerol (Fig. 5). Speculation The findings in the piglet, of small increases in VO2 after norepinephrine infusion and the lack of a significant lowering of VO2 response when norepinephrine challenge was preceded by nicotinic acid administration, contrast with those observed in adults of other species studied and preliminary results found in older piglets. It is therefore suggested that the newborn piglet has a relative inability to increase oxidation of norepi-nephrine-mobilized FFA and that this may improve with increasing postnatal age.