REGION-SPECIFIC RADIOIMMUNOASSAY FOR HUMAN CHROMOGRANIN A

Abstract

A region-specific radioimmunoassay (RIA) for human chromograninA (CgA) was developed using synthetic , based on the amino acid sequence reported by Konecki er aZ. ( serum raised in a rabbit, 1251human CgA(344-374) as tracer and synthetic human CgA(3-44-374) as standard were employed for development of the assay system. The standard displacement curve was parallel to the dose response curves of human plasma, urine, saliva and tissue extracts. The minimum detectable limit of the assay system was approximately 1.80 fmol/tube. The immunoreactive (IR) CgA level of human normal plasma was 0.3li0.05 pmol/mL (meaniSD, 11:25). Plasma IR-CgA levels in patients with renal failure (l.74il.l5 pn1ol/mL, n:28), pheochromocytoma (l.67i0.89 pmol/mL, n =4), thyroid carcinoma (1.90+0.72 pmol/mL, n=4), pituitary adenoma (2.71i0.90 pmol/mL, 11:5) and rectal carcinoid tumour (2.70 pmol/mL, n: 1) were significantly higher when compared to that in normal healthy subjects. Intra-and inter-assay variances in the assay were 2.4-6.4% and 6.5-13.9%, respectively. Recovery of human CgA(344-374) added to plasma ranged from 85.4% to 99.3%. Gel filtrations of human plasma on Sephadex G-75 column using l M acetic acid as eluent revealed the existence of major IR-CgA having approximately 58-60l<Da. These results indicate strongly that the present assay system is valuable for the measurement of IR-CgA in human plasma. In addition, the detectable amounts of IR-CgA were also found in human urine and saliva.