Depression of serum alkaline phosphatase activity by human serum albumin.

The daily intravenous administration of 50 gm. of concentrated saltpoor human serum albumin’ produces a rise in serum albumin level and a decline in urinary calcium and phosphorus excretion (1). These latter changes have been interpreted as evidence for an albumin-induced stimulation of osteogenesis (2). The consistent finding of a concomitant depression of serum alkaline phosphatase activity was thus unexpected, inasmuch as we believe that, in the absence of liver disease, serum alkaline phosphatase is an index of osteoblastic activity. Fig. 1 illustrates the relation observed between serum alkaline phosphatase and serum albumin levels in eleven experiments on six patients. In general, as the serum albumin level rose, the serum alkaline phosphatase activity decreased 50 to 100 per cent. There was no concomitant constant change in serum globulin levels. The magnitude of depression of serum alkaline phosphatase activity was considerably greater than could be explained by expansion of plasma volume, as judged by decrease in blood hemoglobin concentration and hematocrit. The experiments in vitro which follow were designed to clarify the nature of this unexpected relation between human serum albumin and serum alkaline phosphatase activity.