Effect of low-level lifetime exposure to cadmium on calciotropic hormones in aged female rats

The effect of low-level lifetime exposure to cadmium (Cd) on calciotropic hormones and the possible association between the Cd-induced disorders in bone metabolism and these hormones were investigated on a female rat model of human environmental exposure in areas unpolluted by this metal. For this purpose, the concentrations of 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D (1,25(OH)(2)D), calcitonin (CT) and parathormone (PTH) were measured in the serum of control and Cd-exposed (1 mg Cd/l in drinking water for 24 months) female rats. Calcium (Ca) and inorganic phosphorus (P-i) serum concentrations, renal tubular reabsorption of Ca (TRCa) and phosphate (TRP) and the glomerular filtration rate (GFR) were estimated as well. Moreover, 1,25(OH)(2)D, metallothionein (MT) and Cd were determined in the kidney. The exposure to Cd led to a decrease in the serum concentrations of 25OHD and 1,25(OH)(2)D (by 50 and 31%, respectively) and the concentration of 1,25(OH)(2)D in the kidney mitochondrial fraction (by 55%). The serum concentrations of CT and PTH increased (5.2-fold and by 29%, respectively) and those of Ca and P-i were unchanged, whereas the TRCa, TRP and GFR decreased due to the exposure to Cd. The results give evidence that the low lifetime exposure to Cd disturbs the metabolism of calciotropic hormones and damages the reabsorptive and filtrative function of the kidney in aged female rats. Numerous correlations noted between calciotropic hormones and the indices of kidney function, and indices of bone turnover and bone mineral status (bone mineral content and density) of these females indicate a relationship between these hormones and the kidney functional status and bone metabolism. The results of the present study together with our previous findings on the bone status in the experimental model allow for the conclusion that the low lifetime exposure to Cd by affecting the metabolism and proper function of calciotropic hormones may contribute to the advancement of bone damage at the elderly.