Since studies in animals and humans have shown that
parathyroid hormone can stimulate bone formation and increase trabecular bone, and patients with primary and
secondary hyperparathyroidism may exhibit
osteosclerosis, we evaluated the effect of short-term administration of human
parathyroid hormone, hPTH-(1--34), in patients with
osteoporosis. Six patients with
osteoporosis underwent detailed studies including blood and urinary measurements of
calcium, phosphate, and
magnesium; 47Ca kinetic studies; and 18-d balance studies before and during the short-term administration (3--4 wk) of a daily
subcutaneous injection of hPTH fragment 1--34 given as 450 or 750 U/dose. The mean fasting plasma
calcium values rose slightly after hPTH-(1--34) administration, primarily in the high-dose group. There was no difference in the mean fasting plasma
inorganic phosphate levels. The mean daily urinary excretion of
calcium and
phosphate was significantly increased in patients given the higher dose. In patients given 750 U, net intestinal
calcium absorption increased,
phosphate absorption increased,
calcium balance improved, and
phosphate balance improved. In patients given 450 U,
calcium balance and
phosphate balance worsened. 47Ca kinetic studies showed a minimal increase in bone accretion rate, a decrease in the mean transit time of
calcium in the exchangeable pools, and a decrease in the exchangeable-pool size. In all six patients there was an increased renal clearance of 47Ca as a result of hPTH-(1--34) administration. These studies indicate that low doses of
parathyroid hormone may promote bone formation, whereas higher doses clearly have an adverse effect on the skeleton.