Biomedical subjects

W O Hartzell

Publications and source records attributed to W O Hartzell.

3 recordsLinked to original sources

PubMed1991

Ascorbic acid and dehydroascorbic acid measurements in human plasma and serum.

We investigated whether circulating ascorbic acid in humans is protein bound or free and whether ascorbic acid exists in its reduced form alone as ascorbic acid or in its reduced and oxidized forms as ascorbic acid and dehydroascorbic acid, respectively. Ascorbic acid and dehydroascorbic acid were determined by using HPLC with coulometric electrochemical detection, and protein binding was determined by centrifugal ultrafiltration. Ascorbic acid was free in plasma and serum of normal, healthy volunteers, 10 men and 10 women. Ascorbic acid was detectable only in its reduced form. However, dehydroascorbic acid could be made to appear in samples processed under oxidizing conditions. Because circulating ascorbic acid is free and is detected only as reduced vitamin, ascorbic acid may be available without intermediates for peripheral utilization. Dehydroascorbic acid may not be present in plasma and serum of normal humans unless assay conditions permit ascorbic acid oxidation.

Adult↗

PubMed1989

Ascorbic acid within chromaffin granules. In situ kinetics of norepinephrine biosynthesis.

Ascorbic acid requirements for norepinephrine biosynthesis were investigated in intact bovine chromaffin granules using the physiologic substrate dopamine and a novel coulometric electrochemical detection high pressure liquid chromatography system for ascorbic acid. 10 mM external dopamine, 1 mM Mg-ATP, and 1 mM ascorbic acid produced maximal norepinephrine biosynthesis without granule lysis. When external ascorbic acid was omitted, intragranular ascorbic acid was consumed in a 1:1 ratio with respect to norepinephrine biosynthesis. The initial concentration of intragranular ascorbic acid was 10.5 mM, which was depleted in stepwise fashion to 15 lower concentrations over the range of 9.2-0.2 mM. Chromaffin granules containing these varying concentrations of intragranular ascorbic acid were then incubated with 1 mM exogenous ascorbic acid, and norepinephrine biosynthesis from dopamine was determined. The apparent Km of norepinephrine biosynthesis for intragranular ascorbic acid was 0.57 mM by Eadie-Hofstee analysis and 0.68 mM by Lineweaver-Burk analysis. These data indicate that intragranular ascorbic acid is available and required for norepinephrine biosynthesis, that ascorbic acid is a true co-substrate for dopamine beta-monooxygenase, and that intragranular ascorbic acid is maintained by extragranular ascorbic acid. Continued norepinephrine biosynthesis in granules is dependent on both intragranular and extragranular concentrations of the vitamin. Furthermore, in situ kinetics of dopamine beta-monooxygenase for ascorbic acid may be most accurately determined using intact granules and the true physiologic substrate.

Adrenal Medulla↗

PubMed1989

Ascorbic acid analysis using high-performance liquid chromatography with coulometric electrochemical detection.

A method for the detection of ascorbic acid using high-performance liquid chromatography with coulometric electrochemical detection and a technique for stabilization of the vitamin are described. Since less than 1 pmol of ascorbic acid can be detected, this assay provides significantly greater sensitivity than nearly all of the currently available procedures. Stabilization of 10 pmol or less of ascorbic acid at room temperature for up to 4 h and for several weeks at -70 degrees C facilitates storage of a large number of samples and measurement of ascorbic acid using an automated sampling device. This method was used to quantitate the amounts of ascorbic acid in human polymorphonuclear leukocytes and bovine adrenomedullary chromaffin granules. The calculated concentrations found for human neutrophils (1.35 mM) and bovine chromaffin granules (10.0 mM) are in agreement with previously published data. The assay is suitable for the determination of ascorbic acid in biological samples where only a small amount of tissue is available or very low amounts of ascorbic acid are found. This method is the first application of coulometric electrochemical detection to ascorbic acid HPLC analysis.

Animals↗