Effects of disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP) in adult normal and selectively parathyroidectomized rats. I. Effects on plasma calcium, bone tissue, and adrenal glands at low or normal calcium intake.

One-year-old intact and selectively parathyroidectomized rats were given a normal or low calcium diet for 8 months and, during the last 3 weeks, diphosphonates (EHDP) at a low dose level of 1.0 mg EHDP/kg body weight/day intraperitoneally. The administration of EHDP impaired the animals' ability to maintain the blood calcium level during a low calcium intake. Calcium-deficient intact animals had significantly reduced plasma calcium during EHDP treatment, while calcium-deficient parathyroidectomized animals showed no further reduction. Calcium deficiency alone resulted in osteoporosis which was prevented by parathyroidectomy. The short period of EHDP treatment had no significant effect on the bone mass in control, osteoporotic, and parathyroidectomized animals. The calcium accretion rate by bone became significantly increased upon a low calcium intake in intact rats but not in parathyroidectomized ones. This increase was counteracted by EHDP which gave rise to reduced accretion in both parathyroidectomized and osteoporotic animals. In addition EHDP caused hypertrophy of the adrenal cortex in all treated groups.