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

Abstract

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 α₁-antitrypsin, albumin and α₂-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 α₁-antitrypsin and 0.063 for albumin, but lower, 0.040, for α₂-macroglobulin. Thus these increases, being related to molecular size, were not simply caused by posture induced changes of plasma volume. Considering the results for each individual we found a constant difference between the increase of α₁-antitrypsin and α₂-macroglobulin of about 0.030 for the whole range of increases (i.e. for α₁-antitrypsin 0–0.15). In contrast, the effects of recumbency were independent of molecular size. The mean, fractional decreases in concentrations induced by changing of position from sitting (B) to lying (C) were approximately 0.065 for all three proteins.

Key Words:

• albumin
• α₁-antitrypsin
• blood sampling
• α₂-macroglobulin
• posture