STUDIES OF ANTIRICKETIC ACTIVITY IN SERA FROM PATIENTS WITH DISORDERS OF CALCIUM METABOLISM AND PRELIMINARY OBSERVATIONS ON THE MODE OF TRANSPORT OF VITAMIN D IN HUMAN SERUM*

Abstract

Using rachitic rats for bioassay the mean antirachitic activity of sera from 18 normal subjects was equivalent to 2 IU of vitamin D/ml. Hypo-parathyroid patients receiving vitamin D2 had much increased activity in their sera, but the degree of activity could not be accurately predicted from either the dose of the vitamin or the induced increase in Ca concentration of the sera. No increase in antirachitic effect was found in the sera of patients with.various non-vitamin D-induced hypercalcemic states, including patients with hyperparathyroidism, the milk-alkali syndrome and sarcoidosis. Moreover, failure of vitamin D absorption alone did not account for the hypocalcemia in 3 patients with non-tropical sprue. The vitamin D activity of sera was stable even at room temperature and was also non-ultrafilterable. On starch block electrophoresis the predominant antirachitic effect was limited to the area of the alpha globulins. The physical and electro-phoretic characteristics were identical whether vitamin D was added to serum in vitro or in vivo.