Biomedical subjects
Publications and source records attributed to I N Mefford.
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The depolarization-coupled efflux of endogenous ascorbate is demonstrated using rat synaptosome preparations and a rat cortical cup method. Ascorbate and catecholamines (monitored as a methodological control) were quantitated by high pressure liquid chromatography with electrochemical detection. In vitro potassium ion induces ascorbate efflux in a concentration-dependent, although calcium ion-dependent, manner. Veratridine also induces ascorbate efflux and its effect can be blocked by tetrodotoxin. In vivo, ascorbate efflux was likewise stimulated by increased potassium ion and by veratridine. In addition, electrical stimulation of medial lemniscus was accompanied by an increased efflux of ascorbate from somatosensory cortex. These results are intriguing in light of the recent evidence for the interaction of ascorbate with several neurotransmitter systems.
The effect of acute phenylethanolamine-N-methyltransferase (PNMT) inhibition on rat brain catecholamine concentrations was studied. All PNMT inhibitors tested were effective in depleting hypothalamic and brain stem epinephrine. Norepinephrine concentrations were unaffected; however, dopamine levels were increased in all areas studied. While several possible explanations are offered for this phenomenon, the mechanism is not yet understood.
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Tryptophan and many of its indole metabolites were separated using reversed-phase high-performance liquid chromatography (HPLC) and determined using electrochemical detection. This was accomplished isocratically using an acetate--citric acid eluent with various amounts of methanol. Brain and pineal tissue was analyzed for several tryptophan metabolites. Tissue preparation required only homogenization in acidic solution and centrifugation prior to application to the HPLC column. Detection limits in the low picogram range were found for those indoles separated.
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