Abstract
The intestinal surface microclimate pH was measured in rat and man in vitro and rat in vivo using a pH-microelectrode. The mechanism of its creation and maintenance, its role in the absorption of nutrients particularly folate, and its variation in normal and diseased human intestinal conditions was investigated.The maximum acidity of the surface microclimate was measured in the proximal jejunum. The surface acid microclimate is created by the external hydrolysis of adenosine triphosphate (ATP) produced intracellularly through aerobic metabolism, by mucosally located ATPase. The hydrogen ions of the microclimate are retained at the surface by the hydrated glycocalyx. Normal intracellular aerobic metabolism, adequate amount of glucose or other metabolisable substrates that produce enough quantities of ATP and an active mucosally located ATPase in sufficient amount, together with a structurally intact and biosynthetically complete glycocalyx are the necessary requirements for the creation and maintenance of a normal surface acid microclimate.
The absorption of folic acid and 5-meTHF was studied in rats using the everted sac technique. It was demonstrated that folate absorption occurs preferentially in the proximal jejunum but decreases distally. The experimental evidence was inconsistent with the concept of an active specific carrier transport mechanism but supported a model of facilitated passive diffusion of folates after conversion to neutral forms in the surface acid microclimate. An elevation in the surface microclimate pH was found to cause a decrease in folate absorption. 5-meTHF does not undergo metabolic alteration during transport, but a considerable amount of folic acid is metabolised.
A secondary isotopic effect during folate absorption was observed in which the 3H-labelled species was absorbed at a faster rate than the 14¢-labelled and unlabelled species. This phenomena was studied and possible explanations discussed.
The surface acid microclimate was also measured in normal human health and diseased conditions of the small intestine using jejunal biopsies. It was found that the surface acid microclimate exists at the human intestinal surface and that an elevation in its pH occurs in coeliac disease, Crohn's disease and in subjects with nonspecific diarrhoea with abnormal histology. The increase in the surface pH observed with these clinical states was found to be associated with a decrease in serum folate levels.
The present investigation has provided evidence that the surface acid microclimate is a normal physiological phenomena of a healthy small intestine, and that folate ts absorbed by means of a facilitated passive diffusion after conversion into a neutral form in the surface acid microclimate.
Date of Award | 1981 |
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Original language | English |
Awarding Institution |
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Keywords
- surface properties
- mammalian small intestine
- nutrient absorption
- health
- disease