Effects of posture on concentrations of serum proteins in healthy adults. Dependence on the molecular size of proteins.

The effect of posture on changes in protein composition of serum and its dependence on molecular size has been investigated in forty individuals classified by age and sex. Blood specimens were drawn (A) at 0700 hours with persons still resting in bed after an overnight sleep; (B) at 0815 hours, in sitting position after 1 h of moderate exercise and again (C) at 0915 hours, lying in bed after 1 h of recumbency. Concentrations of alpha 1-antitrypsin, albumin and alpha 2-macroglobulin in serum were determined with high analytical precision. The mean fractional increases of concentrations from lying (A) to sitting (B) were 0.069 for alpha 1-antitrypsin and 0.063 for albumin, but lower, 0.040, for alpha 2-macroglobulin. Thus these increases, being related to molecular size, were not simply caused by posture induced changes of plasma volume. Considering the results of each individual we found a constant difference between the increase of alpha 1-antitrypsin and alpha 2-macroglobulin of about 0.030 for the whole range of increases (i.e. for alpha 1-antitrypsin 0-0.15). In contrast, the effects of recumbency were independent of molecular size. The mean, fractional decreases in concentration induced by changing of position from sitting (B) to lying (C) were approximately 0.065 for all three proteins.