THE INFLUENCE OF DIETARY CALCIUM ON THE TISSUE DISTRIBUTION OF Cu, Zn, Mg & P AND HISTOLOGICAL CHANGES IN THE DIGESTIVE GLAND CELLS OF THE SNAIL ACHATINA FULICABOWDICHM

Abstract

Dietary calcium had a varying effect on the concentration of other metals located in the tissues and excreted in the faeces. Faecal phosphate, copper and zinc concentrations decreased with increased dietary calcium but showed a peak of excretion 10–12 weeks after the beginning of the experiment, while the total amounts of the studied elements lost in the faeces increased. Phosphate values in the digestive gland of snails on calcium-supplemented diets were lower than metal values found in control snails. Although the digestive gland magnesium concentrations were always lower and copper levels higher than the snails on the omnivorous diet, the trend was for a decrease in tissue magnesium and copper with increased calcium in the diet. In foot tissue, the trend was towards a decrease in Mg with decreased dietary calcium. The zinc concentration in the digestive gland and foot of snails on the omnivorous diet was not different from the zinc levels in snails on the three highest calcium-supplemented diets. It is suggested that high levels of dietary calcium might act as an environmental stressor characterised by changes in the morphology and histo-chemistry of the digestive tubules.