K. N. Sivasubramanian

Fat digestion in the stomach of premature infants: I. Characteristics of lipase activity

Lipolytic activity was studied in gastric aspirates of 13 premature infants of birth weight 1,050 to 1,786 gm. All infants received a diet of infant formula fed by gastric tube. Gastric aspirates were collected after irrigating the stomach with 2 to 5 ml sterile saline before regular feeding. Lipolytic activity, tested with doubly labeled 3H glyceryl-14 C tripalmitin substrate, was 55.6 +/- 11.7 n mol/min/ml (range 4.2 to 140). The lipolytic activity had a pH optimum of 5.4 and produced partial glycerides (mono and diglycerides), glycerol, and free fatty acids. Lipolysis was inhibited by bile salts. Our findings show that in premature infants, as in adults, digestion of dietary fat starts in the stomach. Since bile salt concentrations are low in premature infants, the amphiphilic reaction products formed (monoglyceride and FFA) could play a significant role in the stabilization of lipid emulsions.

Congenital esophageal atresia: lipase activity is present in the esophageal pouch and stomach.

Lipolytic activity was studied in aspirates from the esophageal pouch and from the stomach of eight infants with congenital esophageal atresia. Lipolytic activity, tested with doubly labeled ([3H]glyceryl, [14C]fatty acid) oong-chain triglyceride was present in esophageal and gastric aspirates. The activity in esophageal aspirates was in the range of 2.7–130 nmol/min/ml aspirate and that in gastric aspirates was in the range of 2.9–40.4 nmol/min/ml aspirate. The reaction products of lipolytic activity in esophageal and gastric aspirates were a mixture of mono- and diglycerides, blycerol, and free fatty acids. The lipolytic activity at the two sites—esophagus and stomach—varied with respect to pH optimum (5.0–7.6 and 6.0–6.5, respectively) and reaction products (glycerol 41.6±20% and 7.3±4.6%, respectively). These findings confirm the earlier observations that digestion of dietary fat is initiated in the stomach and suggest that the lipolytic activity present in gastric contents originates concomitantly from the oral-esophageal area as well as from the stomach. These studies do not exclude the possibility that the lipolytic activity in the stomach of infants with esophageal atresia could originate in regurgitated intestinal contents.

1115 LIPID CLEARING IN PRETERM INFANTS: RELATIONSHIP OF LIPOLYTIC ACTIVITY TO GESTATIONAL AGE AND LIPID LOAD

To determine the development of the lipid clearing mechanism, we have measured serum postheparin lipolytic activity (PHLA), triglyceride (TG) and free fatty acid (FFA) levels in 18 preterm infants, gestational age (G.A.) 25-32 wks, aged 16±1.5 days. Intralipid (I), 0.5 g/kg, was infused without or (after 1-4 days) with heparin (H), 10 U/kg for 4 h and blood was collected at 0, 10, 30, 120 and 240 min of infusion. PHLA (1 unit (U)=1 μmol FFA released from tri-3H olein/ml/h), TG and FFA were measured in all serum specimens. The data show:1. TG clearing develops at 27-28 wks G.A.: PHLA is low <27 wks, highly variable at 27-28 wks and adequate >29 wks. 2. A single bolus of H has only a transient effect on I clearance. 3. PHLA may be depleted by prolonged I infusion-correlation between PHLA and cumulative I infused was r=-0.53, p<0.02 (n=18). We conclude that infants <28 wks G.A. are most susceptible to hepatic and pulmonary complications following prolonged I infusion. (Support NIH grant HL-19056)

430 FAT DIGESTION IN THE STOMACH OF PREMATURE INFANTS: ORIGIN OF THE LIPOLYTIC ACTIVITY

Digestion of dietary fat in the adult is intitiated in the stomach by a lipase similar to that present in lingual serous glands (Hamosh et al. J. Clin. Invest. 55: 908, 1975; Lab. Invest. 37, 1977). Recently, we have reported similar activity in gastric aspirates of premature infants (Hamosh et al. Physiologist 20: 40, 1977). In order to determine the origin of the lipase, we have tested esophageal and gastric aspirates obtained from four infants with congenital esophageal atresia. Lipolytic activity (tested with doubly labeled 3H-glyceryl-14C-tripalmitin) was present in both esophageal (14.24 ± 10.6 n mol/ml/hr) and gastric (6.97 ± 2.31 n mol/ml/hr) aspirates; the reaction products were partial glycerides, glycerol and free fatty acids; pH optimum was 5.4. The data support previous observations that lipolytic activity in the stomach is due to enzymes secreted from the oro-pharynx (tongue). However, lipolytic activity in the stomach of these children strongly suggests the presence of a gastric lipase. (Supported by Grant NIH HD10823).