Chemistry & Biochemistry

9 Continuous gastric pH monitoring offers the opportunity to evaluate gastric acid secretion in humans without the need for collection of gastric aspirates. However, gastric emptying may be an important variable for the accurate measurement of gastric acid secretion using continuous gastric pH monitoring. We conducted an in vitro study (phase I) to evaluate the effect of gastric emptying on gastric pH. The in vitro study used a laboratory model in which continuous pH monitoring of a standard formula (Nutramigen, 100 mL) in a reservoir was performed while varying both the reservoir emptying rate (10% to 80%) over 1 hour and the amount of added acid (2 to 15 mEq/h: in vivo equivalent of 6 to 45 mEq/m 2 BSA/h). An in vivo study (phase II) was then performed in 28 infants less than 6 months of age who had gastroesophageal reflux (GER) documented by 18-to 24-hour esophageal pH monitoring. At the end of esophageal pH monitoring, the pH electrode was advanced into the stomach for measurement of gastric pH continuously for 2 hours after a feeding of Nutramigen formula (300 mL/m 2 BSA). Each patient also had a radionuclide gastric emptying study performed with the same volume of Nutramigen formula. In the in vitro model, the reservoir pH (% time pH <4) was proportional to the reservoir emptying rate only when acid was added at <15 mEq/h (<45 mEq/m 2 BSA/h}. Reservoir pH was independent of reservoir emptying rate when acid was added at 15 mEq/h (45 mEq/m 2 BSA/h). Using the in vitro model as a reference for the in vivo studies, postprandial gastric acid secretion was estimated at >45 mEq/m 2 BSA/h in 6 of 28 (21%) infants and <9 mEq/m 2 BSA/h in 15 of 28 (54%) infants with GER. In conclusion, reservoir emptying affected the measurement of reservoir pH at acid secretion levels under 15 mEq/h (45 mEq/m z BSA/h). In most infants, any measurement of gastric acid secretion by continuous gastric pH monitoring must also account for the rate of gastric emptying.

A detailed time study of the incorporation of label from sodium-[l-14 C]acetate, [1-14 C]ethanol, and [2-14 C]glucose into the aspartyl moiety of N -acetylaspartic acid (NAA) was conducted. As expected the specific activity of aspartate increased rapidly with time and peaked within 15 20 min after which it fell sharply: but significant!). that of the aspartyl moiety of NAA rose very slowly even after the specific activity of aspartate had fallen to less than I per cent of the peak values. A rat brain microsomal free supernatant preparation was shown enzymatically to incorporate label from sodium-[l-14 C]acetate into the t-RNA fraction from which was isolated N-[l-14 C]acetylaspartic acid. From these observations we were inclined to speculate that NAA-t-RNA may serve as an initiator of neuronal protein synthesis. ALTHOUGH N-acetylaspartate (NAA) has been found to occur in large quantities in brain, 5-7 Jln1o1/g (TAL-LAN et al., 1956; GEBHARD & VLLDSTRA, 1964)~ its functional and metabolic importance is as yet unclarified. Many investigators reported that within short periods of time after the administration of labelled precursors. very little radioactivity is incorporated into the aspartyl moiety of NAA, as compared to that in other amino acids, suggesting that endogenous NAA might be metabolically inert (JACOBSON, l958;

Continuous gastric pH monitoring offers the opportunity to evaluate gastric acid secretion in humans without the need for collection of gastric aspirates. However, gastric emptying may be an important variable for the accurate measurement of gastric acid secretion using continuous gastric pH monitoring. We conducted an in vitro study (phase I) to evaluate the effect of gastric emptying on gastric pH. The in vitro study used a laboratory model in which continuous pH monitoring of a standard formula (Nutramigen, 100 mL) in a reservoir was performed while varying both the reservoir emptying rate (10% to 80%) over 1 hour and the amount of added acid (2 to 15 mEq/h: in vivo equivalent of 6 to 45 mEq/m 2 BSA/h). An in vivo study (phase II) was then performed in 28 infants less than 6 months of age who had gastroesophageal reflux (GER) documented by 18-to 24-hour esophageal pH monitoring. At the end of esophageal pH monitoring, the pH electrode was advanced into the stomach for measurement of gastric pH continuously for 2 hours after a feeding of Nutramigen formula (300 mL/m 2 BSA). Each patient also had a radionuclide gastric emptying study performed with the same volume of Nutramigen formula. In the in vitro model, the reservoir pH (% time pH <4) was proportional to the reservoir emptying rate only when acid was added at <15 mEq/h (<45 mEq/m 2 BSA/h}. Reservoir pH was independent of reservoir emptying rate when acid was added at 15 mEq/h (45 mEq/m 2 BSA/h). Using the in vitro model as a reference for the in vivo studies, postprandial gastric acid secretion was estimated at >45 mEq/m 2 BSA/h in 6 of 28 (21%) infants and <9 mEq/m 2 BSA/h in 15 of 28 (54%) infants with GER. In conclusion, reservoir emptying affected the measurement of reservoir pH at acid secretion levels under 15 mEq/h (45 mEq/m z BSA/h). In most infants, any measurement of gastric acid secretion by continuous gastric pH monitoring must also account for the rate of gastric emptying.

■ ■ ■ ■ ■ ■ ■ A EDITORA ATLAS se responsabiliza pelos vícios do produto no que concerne à sua edição (impressão e apresentação fim de possibilitar ao consumidor bem manuseá-lo e lê-lo). Nem a editora nem o autor assumem qualquer responsabilidade por eventuais danos ou perdas a pessoa ou bens, decorrentes do uso da presente obra.