The activity of phospholipase A2 from snake venom to hydrolyze bilayers of phosphatidylcholines is greatly enhanced by the presence of the hydrolysis products, lysolecithin and fatty acid, in the bilayer. The fluorescence of several probes of membrane structure was used to monitor changes in bilayer physical properties during vesicle hydrolysis. These changes were compared to emission spectra and fluorescence polarization results occurring upon direct addition of lysolecithin and/or fatty acid to the bilayer. The excimer to monomer ratio of 1,3-bis(1-pyrene)propane was insensitive to vesicle hydrolysis, suggesting that changes in the order of the phospholipid chains were not relevant to the effect of the hydrolysis products on phospholipase activity. The fluorescence of 6-propionyl-2-(dimethylamino)-naphthalene (Prodan) suggested that the polarity of the bilayer in the region of the phospholipid head groups increases as the hydrolysis products accumulate in the bilayer. The fluorescence of 6-dodecanoyl-2-(dimethylamino)naphthalene (Laurdan) confirmed that such effects were restricted to the bilayer surface. Furthermore, the lysolecithin appeared to be the product most responsible for these changes. These results suggested that lysolecithin increases the activity of phospholipase A2 during vesicle hydrolysis by disrupting the bilayer surface, making the phospholipid molecules more accessible to the enzyme active site.
BACKGROUND Neonates with necrotizing enterocolitis (NEC) have higher calprotectin levels in stool than do healthy neonates. However, it is not known whether high stool calprotectin at the onset of bowel symptoms identifies neonates who truly have NEC vs. other bowel disorders. STUDY DESIGN Neonates were eligible for this study when an x-ray was ordered to “rule-out NEC”. Stool calprotectin was quantified at that time and in a follow-up stool. Each episode was later categorized as NEC or not NEC. The location of calprotectin in the bowel was determined by immunohistochemistry. RESULTS Neonates with NEC had higher initial and follow-up stool calprotectin levels than did neonates without NEC. Calprotectin in bowel from neonates with NEC was within neutrophil extracellular traps (NETs). CONCLUSION At the onset of signs concerning for NEC, fecal calprotectin is likely to be higher in neonates with NEC. Calprotectin in their stools is exported from neutrophils via NETs.
Objective: Studies in adults indicate that ampicillin, in a dose-dependent manner, impairs platelet function and moderately prolongs the bleeding time (generally by 60 to 90 s). Unlike aspirin, the inhibition induced by ampicillin involves both reversible and irreversible mechanisms and is not observed immediately after initial dosing (generally requiring approximately 24 h). Ampicillin is administered commonly to neonatal intensive care unit (NICU) patients, but its effect on bleeding time in this population has not been reported earlier.Study Design: We performed neonatal template bleeding times and platelet function analyzer (PFA)-100 tests on 15 NICU patients before and at various intervals after intravenous ampicillin dosing.Result: Neonates were only studied if no beta-lactam antibiotics were administered to their mother during labor, and if they had ampicillin ordered by the clinician at a dose of 50 to 100 mg kg -1 every 12 h. Subjects ranged from 33 to 41 weeks gestation and weighed 1760 to 3835 g. Bleeding times before the first ampicillin dose (n ¼ 15) averaged 134 s (95% confidence interval (CI), 120 to 148 s) and PFA-100 times averaged 123 s (95% CI, 96 to 149 s). After the first dose of ampicillin (n ¼ 5), bleeding times and PFA-100 times did not increase, but after the third (n ¼ 5) and fourth doses (n ¼ 4) bleeding times lengthened by an average of 60 s (95% CI, 37 to 83 s, P<0.001) and PFA-100 times lengthened by an average of 20 s (95% CI, À20 to 60 s, P ¼ 0.15).Conclusion: Ampicillin administered intravenously to NICU patients prolongs the bleeding time, with a magnitude-of-effect and time-to-effect similar to that shown earlier in adults.
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