Distribution 0f chromogranin a-like peptides in the rat

The aim of the present study was to investigate the distribution and molecular heterogeneity of chromogranin A (CgA)-related peptides in rat tissues using multiple region-specific radioimmunoassays (RIAs) for CgA. Rat CgA (rCgA) fragments such as rCgA(1-28), rCgA(94-130), rat pancreastatin(33-51), and rCgA(359-389), which were prepared by solid phase technology, were used as immunogens to produce region-specific antisera in rabbits such as anti-rCgA(1-28) serum RO791, anti-rCgA(94-130) serum RO771, anti-rat pancreastatin(33-51) serum RO871 and anti-rCgA(359-389) serum RO763, respectively. Using this battery of antisera, we developed four types of region-specific RIAs for CgA. Although all four types of RIAs revealed the existence of the IR-CgA in rat tissue extracts, IR-pancreastatin levels were present but in very low concentrations in all of tissues examined. The high level of IR-CgA was detected in pituitary and adrenal gland extracts in all CgA RIAs. The molecular forms of CgA in extracts of pituitary, hypothalamus, adrenal gland, adenostomach and pancreas were examined by gel filtration on Sephadex G75 column. In pituitary and hypothalamic extracts, two major molecular forms of IR-CgA were detected by rCgA(1-28) and rCgA(94-130) RIAs. One form elutes in the region of approximately 66 kDa, and another elutes between 66 kDa and 14 kDa, suggesting the presence of CgA and β-granin. In pancreatic extracts, a large molecular form of IR-CgA eluted in the void volume region, while a β-granin-like component was not detected. Although pancreastatin was isolated originally from porcine extracts, the presence of pancreastatin-like component was not observed by gel filtration of rat pancreatic extracts. In the adrenal gland extracts, the IR-CgA peak was observed, but β-granin-like immunoreactivity was lower than that observed in gel filtration profile of pituitary extracts. In adenostomach extracts, IR-CgA with approximately 66 kDa was mainly detected. In addition, smaller molecule forms with broad peaks were detected by the rCgA(1-28) RIA, suggesting that the processing of CgA in rat stomach may proceed at both N- and C-terminal sites. These results suggest that CgA may be processed in rat tissues differently to produce a variety of molecular forms specific for each tissues. The region-specific antisera for CgA prepared against the synthetic peptides will be valuable for analysis of localization, processing and function of CgA-related peptides.