Parathyroid hormone does not inhibit platelet aggregation.

The suggestion that parathyroid hormone (PTH) is a major uraemic toxin was examined by testing the effects of synthetic human PTH fragments and synthetic bovine PTH on ADP-induced and collagen-induced platelet aggregation. Whereas the bovine parathyroid-gland extracts inhibited platelet aggregation in a dose-dependent manner, none of the synthetic compounds was effective even at high concentrations. It is suggested that the inhibition of platelet aggregation by extracts of bovine parathyroid glands is not caused by PTH fragments and is probably an effect of other constituents contained in the extract. These findings argue against a role of PTH in the pathogenesis of platelet dysfunction and bleeding tendency in uraemia and were supported by platelet-aggregation studies in 6 patients with primary hyperparathyroidism. Platelet aggregation was normal before and unchanged after surgery of the parathyroid glands.