Evaluation of a simplified blood pepsinogen assay

Blood pepsinogen concentrations in cattle were determined, using a simple, direct method based on the hydrolysing effect of serum on buffered bovine albumin substrate (2 g/dl). The amount of tyrosine released was measured at 680 nm, using the Folin and Ciocalteu's colorimetric method. To ensure an optimal digestion in vitro, a glycine-hydrochloric acid buffer (0.1M) was evaluated at various pH. Serum samples with medium (2,591 mU of tyrosine) and high (6,222 mU of tyrosine) pepsinogen concentrations had the highest proteolytic activity at pH 2.5. Substituting albumin by hemoglobin substrate resulted in almost double the amount of hydrolyzed products. For preparation of standard pepsin or pepsinogen curves, the incorporation of serum (activated or inactivated) diminished the tyrosine released to only half the amount obtained without serum. The use of serum or plasma did not significantly affect the results of the test, nor did prolonged storage at -70 C result in marked differences in the results.