IMMUNOREACTIVE CHROMOGRANIN A IN RAT PLASMA AND URINE MEASURED BY REGION-SPECIFIC RADIOIMMUNOASSAY

Abstract

Using four kinds of region-specific radioimmunoassay (RIA) systems for rat chromogranin A (CgA), characterization of immunoreactive (IR)-CgA in rat plasma and urine was carried out in the present study. Among the antisera used for RIAs, anti-rat CgA(]-28) serum recognizes the N-terminal region of rat CgA, anti-rat CgA(94-~]30) serum recognizes the C-terminal region of 5-granin, anti-rat CgA(296-3]4)-NH2 recognizes the C-terminal region of pancreastatin and anti-rat CgA(359-389) recognizes the C-terminal part of CgA, respectively. Dose response curves of IR-CgA in rat plasma and urine were parallel to those of the respective standard curves in the four RIA systems using synthetic peptides corresponding to rat CgA(]-28), rat CgA(94-I30), rat CgA(296-314)-NH; and rat CgA(359-389), respectively. Difference in Gel filtration profiles of rat plasma measured by the RIAs using anti-rat CgA(]-28) serum, anti-rat CgA(94-Z30) serum and anti-rat CgA(359-389) serum suggested the existence of a variety of the processing products. However, IR-CgAs were hardly detected by the CgA(296-3]-4,)-NH; RIA system, when applied the same amount of plasma as used for the other RIAs, suggesting that amount of IR-CgA containing the C-terminal pancreastatin may be extremely low in the rat plasma. On the other hand, major immunoreactivity on the gel filtration of rat urine was eluted at the total volume when assayed by the RIAs using anti-rat CgA(1-28) serum, anti-rat CgA(94~Z30) serum and anti-rat CgA(359-389) serum, respectively. In addition to the low molecular weight immunoreactivity, IR-CgA with higher molecular weight was also detected, when assayed by the RIA with anti-rat CgA(359-389) serum. Besides RIA with anti-rat CgA(296-3]4)-NH; serum, IR-CgA levels in rat plasma and urine were detected by RIAs using anti-rat CgA(Z-28) serum, anti-rat CgA(94-130) serum and anti-rat CgA(359-389) serum, respectively. Using the present antisera, characterization of immunohistochemical staining of IR-CgA was also carried out in endocrine cells in the rat adrenal gland, gastric body, and pancreas.