Chapter 24
Effect of Oxygen Depletion on the Food Digestion
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R. Yamaji, M. Sakamoto, Y. Ohnishi, H. Inui, K. Miyatake, and Y. Nakano Department of Applied Biological Chemistry, Osaka Prefecture University, Sakai, Osaka 593, Japan
Hypoxemia causes anorexia, and consequently results in weight loss. Under chronic hypoxic conditions, weight loss occurred even when food intake was adequate, indicating that hypoxia, but not anorexia, resulted in weight loss. Furthermore, when conscious rats were acutely exposed to normobaric hypoxia (10.5% or 7.6% O ), hypoxia inhibited the gastric emptying and the gastric acid secretion and increased the plasma gastrin concentration. Thus, acute hypoxemia lowers gastric function. However, the hypoxia-suppressed gastric acid secretion was gradually recovered during chronic exposure to hypoxia. 2
Hypoxemia, which results in a reduction of arterial oxygen pressure in the blood, and a lack of oxygen in tissues, is a biological state that mammals, including humans, may encounter acutely, or chronically. It may come by way of cardiopulmonary diseases, pernicious anemia, and residence at high altitudes. Hypoxemia resulting from various clinical situations, and trekking or expeditions to high altitudes, is associated with weight loss or failure to gain weight. Several possible explanations for this phenomenon are; 1) a decreased food intake due to anorexia (1-4); 2) an increased energy requirement due to an increased basal metabolic rate (5-8); 3) a loss of body water through diuresis (1, 9), or through increased respiratory and insensible losses (10); and 4) a decreased absorption and digestion (1,4, 10-16). The amount and rate of weight loss seems to depend on the length of hypoxia (short- or long-term), and the degree of hypoxia (severe or mild), suggesting that weight loss via hypoxia varies with the experimental procedures. Although several investigators have studied absorption tests in people with hypoxemia resulting from lung and heart diseases, pernicious anemia and residence at high altitude, contradictory results for both absorption and digestion have been reported. We report in this paper, that chronic hypoxia results in weight loss, and that acute hypoxia inhibits a gastric emptying and a gastric acid secretion when conscious rats are exposed to 10.5% or 7.6% O2 hypoxia.
©1998 American Chemical Society Shibamoto et al.; Functional Foods for Disease Prevention II ACS Symposium Series; American Chemical Society: Washington, DC, 1998.
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Weight Loss and Malabsorption Hypoxemia causes anorexia, and consequently results in weight loss (1-4). To study the effect of hypoxia on dietary intake, rats were exposed to 7.6% 02 hypoxia. Before the experiment began, five-week-old male Wistar rats, weighing 110-120 g, were housed individually in stainless steel cages. They were adapted to a meal-feeding schedule, which allowed free access to a nonpurified rat diet (CE2: Clea Japan, Tokyo) for 4 h (from 1100 to 1500 h) every day, for 2 weeks. On the day of the experiment, rats were transferred to 7.6% 62 hypoxic chamber immediately, before 4 h of consuming diet. The amount of diet, which the hypoxic rats consumed for 4 h, was weighed. As shown in Figure 1, food intake decreased after hypoxic exposure and then was gradually recovered to near the normoxic level during 5 d of hypoxia. Next, the effect of hypoxia on body weight was studied. Body weight in the hypoxic rats was compared to that in the normoxic rats, which were pair-fed. As shown in Figure 2, weight loss due to the decreased food intake was observed after 2 days of hypoxia, whereas there were no significant differences in weight between the hypoxic rats and the normoxic rats with pair-feeding. In contrast, when rats were chronically exposed to hypoxia (more than 3 wk), weight gain in the hypoxic rats was less than that in the normoxic rats with pair-feeding. These results indicate that chronic hypoxia causes weight loss even when food intake is adequate. Thus, chronic hypoxia results in weight loss by factors except for food intake. Absorptive capacity may be associated with weight loss in hypoxia. Therefore, a xylose absorption test has been performed. Milledge (17) found that there was a definite correlation between xylose absorption and arterial oxygen saturation in patients with hypoxemia resulting from chronic respiratory disease, or congenital cyanotic heart disease. Consequently, he predicted that similar changes in xylose absorption occurred in sojourners who experienced decreased arterial oxygen pressure at high altitudes. Boyer and Blume (1) measured urinary xylose excretion during exposure to altitude of 6,300 m in the 1981 American Medical Research Expedition to Everest and found that hypobaric hypoxia decreased the urinary xylose excretion, compared to the sea level. At this altitude, fat absorption also decreases. However, no fat malabsorption at altitudes >4,700 m and no protein malabsorption at altitudes
