Effects of Hyperbaric Hypoxia on Some Enzyme Systems in the Mammalian Liver

Journal of the Arkansas Academy of Science Volume 32 Article 8 1978 Effects of Hyperbaric Hypoxia on Some Enzyme Systems in the Mammalian Liver Dennis A. Baeyens University of Arkansas at Little Rock M. J. Meier University of Arkansas at Little Rock Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Biology Commons Recommended Citation Baeyens, Dennis A. and Meier, M. J. (1978) "Effects of Hyperbaric Hypoxia on Some Enzyme Systems in the Mammalian Liver," Journal of the Arkansas Academy of Science: Vol. 32 , Article 8. Available at: http://scholarworks.uark.edu/jaas/vol32/iss1/8 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact , . Journal of the Arkansas Academy of Science, Vol. 32 [1978], Art. 8 Effects of Hypobaric Hypoxia on Some Enzyme Systems in the Mammalian Liver I DENNIS A. BAEYENSandM. MEIER Department of Biology University of Arkansas at Little Rock Little Rock, Arkansas 72204 ABSTRACT The metabolic effects of hypobaric hypoxic stress on the mammalian liver were studied. The lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH) activity of mouse liver homogenates were measured after exposure to an equivalent altitude of 36,000 feet and compared to controls kept at zero altitude. After six and twelve hour incubation periods, the altitude exposed samples demonstrated a significantly higher LDH activity than controls. SDH activity remained unchanged from controls after six hours but was significantly lower than controls after a 12 hour exposure to altitude. Itis concluded that the changes inenzyme activity reflect a metabolic control mechanism attempting to maintain adequate energy production during periods of exposure to hypobaric hypoxic stress. INTRODUCTION Itis well known that many physiological changes occur in animals during periods of exposure to high altitudes. Over a period of time, some of these changes include hyperventilation, increased vascularity, and increased hemoglobin. These changes can be considered compensatory reactions and are known to aid in the survival of man and other organisms during periods of exposure to lowered oxygen partial pressure at altitude, a condition known as hypobaric hypoxia. The biochemical mechanisms that regulate the adaptation of animals to environmental stress like hypobaric hypoxia are not clear at the present time. Exposure to hypobaric hypoxia could result in a lowered oxygen tension in the tissues, thus, seriously affecting those metabolic processes which are dependent on molecular oxygen. The biochemical and physiological responses to altitude exposure should favor the development of compensatory mechanisms to overcome the effects of the stress. Several attempts have been made to determine if exposure to altitude results in changes in cellular metabolism. For example, the oxygen storage pigment, myoglobin. from both cardiac and skeletal muscle has been shown to increase during prolonged exposure to altitude (Anthony et al, 1959). There are also a number of reports on the effects of altitude exposure on tissue respiration. There is some controversy, however, concerning the findings of these reports. Some workers have reported that tissue respiration is decreased during altitude exposure (Clark et al, 1954); others have claimed that it is increased (Sundstroem and Michaels. 1942); while still others have claimed that it is unchanged (Frehn and Anthony, 1961 ). Our study was undertaken in the hope of clarifying some of the contradictory findings concerning cellular metabolism during exposure to altitude. The specific aim was to examine the effects of hypobaric hypoxia on two hepatic enzymes in the mouse; lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH). By examining the activities of these two enzymes, it was possible to quantitate the effects of hypobaric hypoxia on the activity of both the Embden-Meyerhof pathway and the tricarboxylic acid cycle. There are several problems encountered in trying to deduce the effects of hypobaric hypoxia on the tissues of animals after in vivo exposures to altitude. A particularly important problem is the different effect of hypobaric hypoxia on the blood flow to different organs. For example, severe hypobaric hypoxia results in a dramatic increase in coronary blood flow (Hackel et al, 1954) but only a moderate increase in cerebral blood flow (Lassen, 1959). It is clear that, due to these differences in perfusion, the actual degree of lowering of the intracellular oxygen tension cannot be predicted from most in vivo experiments. In light of this observation, the study of the effects of hypobaric hypoxia on a particular tissue can only be accomplished under conditions of complete ischemia or of controlled blood flow. By employing an in vitro approach in our study it was possible to circumvent the problem of perfusion changes and at the same time to 22 quantitate the direct effects of hypobaric hypoxia on hepatic cellular metabolism. METHODS Female adult Swiss Webster mice (approximate weight 35-40g) were used in all experiments. Mice were killed by cervical dislocation, and pieces of liver weighing approximately 150 mg for the LDH assay or 450 mg for the SDH assay were removed. The tissues were homogenized by a Polytron tissue homogenizer (Brinkman Instruments. Westbury, New York) after addition of 0.1 ml of phosphate buffer (0.034M, pH 7.4) to 1 mg of tissue for LDH and 5 mg of tissue for SDH, respectively. The homogenate was centrifuged (Beckman model LZ-50 Ultracentrifuge) at 20,000 RPM for five minutes after which the supernatant was removed and placed on ice. For incubation. 100 of the supernatant was added to each of 32 I-ml capacity incubation vials. Each incubation vial was tightly capped to prevent evaporation. The rubber middle of each cap was pierced by an 18 gauge hypodermic needle for the purpose of pressure equalization during the hypobaric treatments. The incubation vials were divided into two groups, the controls and the experimentals. The control vials were placed in a desiccator containing filter paper dampened with water and were incubated al ambient barometric pressure. The experimenlals were placed in a 9.3 liter capacity glass vacuum desiccator containing dampened filter paper. A Diaphragm Air Pump (model PV-200. Bell & GossettLeiman Bros., Monroe, LA) was used to create a vacuum equivalent to 23 inches of Hg (altitude equivalent. 36.000 ft) in the experimental (...truncated)