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Title: Local (intestinal) and systemic responses of animals to ingested Phaseolus vulgaris lectins : mechanism of lectin toxicity
Author: Greer, F. M.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1983
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Diets containing high levels of raw kidney beans (Phaseolus vulgaris) are toxic to several species of animals. The main toxic component is a glycoprotein lectin. In nitrogen balance studies the inclusion of raw beans in an otherwise nutritionally adequate diet for rats increased both faecal and urinary losses of nitrogen and resulted in a negative nitrogen balance for the animals. The increased faecal nitrogen loss was due to the binding of the lectin to the luminal surfaces of enterocytes causing a severe disruption of the brush border of the proximal small intestine and resulting in an interference with digestion and absorption of dietary nitrogen. In addition, local hypersensitivity reactions, possibly involving lectin-specific IgE, might cause a stimulation of mucus secretion and an increase in plasma protein flow into the lumen. This would also contribute to the increased endogenous faecal nitrogen loss. The increased output of urinary nitrogen, mainly as urea, however, indicates the existence of systemic catabolic effects. Kidney bean lectins are resistant to intestinal proteolysis and a relatively large proportion of the lectin (1-5%) was shown to be transported across the intestinal barrier, possibly through a specific uptake mediated by receptors on the surface of the enterocyte. Circulating antibodies to the lectin (IgG class) were detected in the serum of bean-fed rats by an enzyme-linked immunosorbant assay. It is suggested that this systemic uptake of lectin and the ensuing immune response could result in hypersensitivity reactions (Type III) and could also affect the functioning of various cells by disrupting their normal metabolism.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available