Lipase and pepsin activity in the gastric mucosa of infants, children, and adults.

The range of activity and the location of lipase and pepsin were determined in the stomach and duodenum of infants, children, and adults. The range of lipase activity in biopsy specimens from the gastric body, in 29 subjects aged from 3 months to 26 years, was 1.8-5.3 U/mg protein (1 U is 1 mumol [3H]oleic acid released from tri-[3H]olein per minute). There were no significant differences among age groups (5-19 months, 2-4 years, 6-10 years, 11-13 years, and 15-26 years). Lipase activity was low or undetectable in the gastric antrum of all subjects. Pepsin activity in specimens from the gastric body ranged from 180 to 780 pepsin units/mg protein (using hemoglobin as substrate). The antrum had significantly lower pepsin activity (P less than 0.001) than the gastric body. As with lipase activity, there were no statistically significant differences in pepsin activity among age groups. Lipase and pepsin activity was also quantified in pinch biopsy specimens from the duodenum and duodenal bulb in 13 subjects. Contrary to lipase activity, which was almost completely absent from the duodenum or duodenal bulb, these sites contained low pepsin activity (9-78 pepsin units/mg protein). The data show that in infants and children, as previously reported in adults, gastric lipase is localized primarily in the gastric body. Tissue pepsin levels and localization, reported here for the first time, are similar to those of lipase, although, contrary to lipase, the gastric antrum has considerable pepsin activity. The identical levels of lipase and pepsin activities in infants, children, and adults indicate that the gastric phase of nutrient digestion is well developed at birth.

Milk lipid digestion in the neonatal dog: the combined actions of gastric and bile salt stimulated lipases.

Intragastric lipolysis may be particularly important for the digestion of milk lipid since milk fat globules are resistant to pancreatic lipase without prior disruption; milk bile salt stimulated lipase (BSSL) may supplement further intestinal hydrolysis. Previous information on gastric lipolysis has been based primarily on in vitro studies using artificial lipid emulsions containing a single component fatty acid and have focused on the preferential release of medium-chain fatty acids. The actual contribution of these enzymes to overall fat digestion in vivo on natural substrates has rarely been studied, however. The neonatal dog is an excellent model in the study of lipid digestion because, like the human, milk lipids are high in long-chain unsaturated fatty acids, milk contains BSSL and gastric lipase is the predominant lipolytic enzyme acting in the stomach. We used a combination of in vivo studies with in vitro incubations to investigate digestion of milk lipid by gastric and milk (BSSL) lipases in the suckling dog. In the first 4 weeks postpartum, 14-41% and 42-60% of milk triacylglycerol was hydrolyzed to primarily diacylglycerol and free fatty acid (FFA) in the first 30 and 60 min in the stomach, respectively. Milk lipid contained high levels (63%) of long-chain unsaturated fatty acids, which were preferentially released as FFA during in vivo gastric lipolysis, consistent with the actions and stereospecificity of gastric lipase. While levels of hydrolysis in gastric aspirates were significantly different (by age and time in stomach) at the start of in vitro studies, total hydrolysis in all incubation systems plateaued at about 65%, suggesting product inhibition by the long-chain FFA, but to a much lesser degree than previously expected from in vitro studies. The magnitude of in vivo intragastric lipolysis was 3- to 6-times greater than that predicted by in vitro assays using either milk lipid or labeled emulsion as substrate, respectively. Prior exposure to intragastric lipolysis resulted in 30% hydrolysis by BSSL compared to 5% hydrolysis without prior exposure. We suggest that previous in vitro studies have largely underestimated the actual degree of intragastric lipolysis that can occur and its activity on long-chain fatty acids; this study indicates the importance of the combined mechanisms of gastric lipase and BSSL to fat digestion in the suckling neonate.

Lipase and pepsin activities in the stomach mucosa of the suckling dog.

The origin of preduodenal lipases was investigated in the suckling dog. In this species, gastric lipase is the main (or only) preduodenal lipase (activity range 1.03-8.32 U/mg protein), lingual-lipase activity being absent or amounting to traces only (0.77-2.3 mU/mg tissue). The localization of lipase activity in the stomach was mapped and compared to that of pepsin. The data show that the highest lipase activity was found in biopsy specimens of gastric mucosa from the cardia area (5.32 +/- 1.29-8.32 +/- 0.93 U/mg protein), and the lowest in the antrum (1.03 +/- 0.16-1.94 +/- 0.43 U/mg protein). Activity was also significantly higher in the mucosa along the greater rather than the lesser curvature of the stomach. Pepsin activity was highest in the cardia and gastric body areas (26.2 +/- 0.89-89 +/- 23.61 and 26.83 +/- 15.98-69.51 +/- 9.82, respectively). Contrary to lipase activity, considerable pepsin activity was present in the antrum (18.17 +/- 4.12-23.07 +/- 5.60 U/mg protein). No difference in pepsin activities was found in the greater as compared to the lesser curvature. The data show similar origin and tissue distribution of gastric digestive enzymes in the suckling dog and human infant. The role of the newborn dog as an animal model for fat digestion in the human infant is discussed.

The natural history of asymptomatic carotid disease in patients undergoing cardiovascular surgery.

Prospective screening of 449 patients undergoing coronary or peripheral arterial revascularization detected asymptomatic cervical bruits in 44 patients (9.8%) and carotid obstruction by Doppler ultrasound in 63 individuals (14.0%). There was poor correlation between cervical bruit and carotid obstsruction. No patient underwent prophylactic casrotid endarterectomy. Three patients had transient ischemic attacks (TIAs), and five had nonfatal strokes perioperatively, only one of which was in the territory appropriate to carotid obstruction. Of 72 surviving patients with asymptomatic carotid disease, 10 (13.9%) had TIAs and one (1.4%) died of stroke during a 2-year follow-up, during which time only two (0.8%) of 254 patients without carotid disease reported symptoms of TIAs. Patients with asymptomatic carotid disease had a significantly higher incidence of perioperative and late deaths (10.6% and 9.2%, respectively), usually of myocardial infarction, as compared to patients without carotid disease (0.3% and 0.8%, respectively, P less than 0.001). Asymp-tomatic carotid disease, although correlating poorly with perioperative stroke in patients undergoing cardiovascular operations, identifies patients at risk of late neurologic events and peroperative or late deaths from myocardial infarction. We do not recommend prophylactic carotid endarterectomy but favor operative intervention if patients develop TIAs during a period of careful follow-up .