Extraction of Prostaglandins from Human Blood

Abstract

EXISTING methods for extracting prostaglandins from tissues or seminal plasma with 70–90% ethanol¹ or acetone² give poor and inconsistent recoveries from blood. Equilibrium dialysis and recovery experiments with labelled and unlabelled prostaglandins show that this is due to binding with precipitated serum albumen (unpublished results of W. G. U.). Plasma globulins and intact blood cells do not seem to interact with the prostaglandins. When precipitation of protein is avoided by using 40–50% ethanol acidified with formic acid, the prostaglandins can be extracted quantitatively into chloroform. The method is as follows: (1) centrifuge heparinized or citrated blood; (2) mix 1 volume each of plasma and saline with 2 volumes of ethanol (analytical grade); (3) extract twice with petrol (boiling point 40°–60° C, 2×2 volumes) to remove neutral fats including carotene; (4) adjust to pH 3–3.5 with formic acid (1–3% v/v); (5) extract twice with amounts of chloroform each equal to the total volume in stage 4; (6) evaporate chloroform in a thin film evaporator at 30° C; (7) re-dissolve residue in 10 ml. chloroform and evaporate to aid the removal of formic acid; (8) blow oxygen-free nitrogen through vessel until odour of formic acid is gone; (9) dissolve in Krebs solution for bioassay or in appropriate solvent for chromatography.