The identification and control of metabolic states.

Abstract

The following paper demonstrates a series of metabolic transitions of cells and tissues and their effects upon the oxidation-reduction state of pyridine nucleotide measured in vivo by a new technique. We have employed a stereotyped set of transitions to segregate the varied responses of different parts of the metabolic chain under appropriate conditions. For example, the rest-activity transition initially involved the mitochondrial space; then it led to a depletion of available substrates and to a condition under which feeding the animal by intravenous injection led to a highly localized and rapid response involving activation of the glycolytic and glycogenolytic mechanisms of the cytoplasm, with subsequent repercussions on the mitochondrial space. The transition from aerobiosis to anoxia, either with toxic agents such as barbituates, primarily affected the mitochondrial space and, in turn, set into action control mechanisms for the more rapid operation of glycolysis in the cytoplasmic space, measured not only by DPN reduction but by tissue analysis of the adenine nucleotide ratios as well. The ability to pinpoint the site of inhibition caused by barbiturates in vivo on the basis of in vitro studies of mitochondria has proved useful in evaluating the novel response of tissues to hyperbaric conditions. Here, our data show that hyperbaric conditions cause a massive change in the oxidation state of the intracellular pyridine nucleotide in the direction of oxidation—a reaction easily read out by fluorometric techniques in vivo. Analytical determinations thoroughly justify this finding and, in addition, support the observation of an increased ATP/ADP ratio in the tissues. Locating this reaction at a site of reversed electron transfer in mitochondria now allows a much better interpretation of the action of possible therapeutic agents.