Calcium metabolism of rats with varying degrees of insulinopenia

Abstract

This paper reports an investigation designed to determine the influence of varying degrees of insulinopenia upon the calcium metabolism of actively growing, alloxan-treated rats fed diets with three levels of calcium. A significant reduction in the skeletal mass (in absolute terms) was observed one month after alloxan administration in rats fed diets with normal or high calcium contents. The impact of insulin deficiency was greater on bone collagen than on the mineral mass, as shown by the increased calcium/hydroxyproline ratio. Alloxan-treated rats showed rather increased levels of PTH which was at variance with respect to control animals and unrelated to the calcium content of the diet. In spite of the high PTH levels, diabetic rats showed significantly diminished rates of bone Ca accretion and resorption. In addition, the animals fed the diet with the normal Ca content, showed significantly reduced areas of osteocytes lacunae and hypocalcemia after 24 h of fasting. The overall information obtained indicates that, in the rat, insulin deficiency more pronouncedly affects organic matrix than mineral turnover. The diabetic state is characterized by an impaired reponse of bone tissue to physiological stimuli, which is attributed to defective cellular activity caused by insulin deficit. Diminished bone resorption is considered to be an adaptative response to preserve bone mass.