IDENTIFICATION OF IMMUNOREACTIVE ATRIAL-NATRIURETIC-PEPTIDE IN THE GALLBLADDER AND BILE JUICE OF RABBIT, PIG AND HUMAN

The presence of immunoreactive atrial natriuretic peptide (irANP) in r abbit, pig and human gallbladders was investigated using radioimmunoas say and immunohistochemistry. Serial dilution curves of gallbladder ti ssue and bile juice extracts were paralleled to the standard curve of atriopeptin III. Gel filtration profiles of gallbladder tissue extract s showed a major peak corresponding to rat pro-ANP. The amounts of irA NP in rabbit, pig and human gallbladders were 30.0+/-12.3 pg/mg (n = 7 ), 7.0+/-2.0 fg/mg (n = 7) and 17.7+/-2.0 fg/mg wet tis sue (n = 8), r espectively. Bile juice was also shown to contain irANP but with small molecular mass. The amounts of irANP in the rabbit, pig and human bil e juice were 25.0+/-2.0 (n = 7) and 0.50+/-0.02 (n = 7), and 1.3+/-0.1 pg/ml (n = 8), respectively. The immunohistochemical staining of the rabbit gallbladder tissue revealed the presence of irANP in the lumina l epithelium and smooth muscle layer. The amount of irANP was higher i n the luminal epithelium than in the rest of the gallbladder tissue fr om rabbits (0.30+/-0.06 vs. 0.10+/-0.01 pg/mu g protein, P<0.01). Thes e findings suggest that ANP may be synthesized and stored in the gallb ladder, and may have a role in the regulation of fluid balance and cys tic motility.