Pituitary adenylate cyclase activating polypeptide (PACAP)-like immunoreactivity in pheochromocytomas

Pituitary adenylate cyclase activating polypeptide (PACAP) is a novel hypothalamic peptide consisting of 38 amino acids [PACAP(1-38)] with a potent stimulatory action on adenylate cyclase in rat pituitary. The presence of immunoreactive (IR-) PACAP in the tumor tissue of pheochromocytomas was studied by radioimmunoassay and immunocytochemistry. The antibody to PACAP was raised in a rabbit injected with a peptide containing amino acids 28-38 of PACAP. This antibody showed no significant cross-reactivity with either PACAP(1-27) or vasoactive intestinal polypeptide. The tumor tissue concentrations of IR-PACAP(1-38) were 0.5-57.5 pmol/g wet weight (n = 13) (24.5 ± 22.4 pmol/g wet weight, mean ± SD), while those in the normal adrenal glands were 3.58 ± 2.02 pmol/g wet weight (n = 7) and those in the adrenal cortical tumors were 5.58 ± 2.02 pmol/g wet weight (n = 6). The IR-PACAP(1-38) concentrations in 7 out of 13 pheochromocytomas exceeded 18 pmol/g wet weight. Sephadex G-50 column chromatography revealed that the IR-PACAP(1-38) in extracts of pheochromocytomas eluted in both the positions of PACAP(1-38) and a larger molecular weight. Reverse-phase high performance liquid chromatography of the tumor extracts revealed a peak in the position of PACAP(1-38) and at least four other peaks. Immunocytochemistry of pheochromocytomas showed numerous immunoreactive cells. The immunostaining was abolished by absorption of the antiserum with synthetic PACAP(1-38). These findings indicate that multiple forms of IR-PACAP(1-38) are present in pheochromocytomas.