Potential methodologic problems with in vivo immunoneutralization of pancreatic polypeptide.

Abstract

Dogs with chronic pancreatic fistulae were given 0.5 ml of nonimmune rabbit serum or antibody S5, an antibody raised against the C-terminal pancreatic polypeptide (PP) hexapeptide. A 3-h infusion of secretin (125 ng/kg/h) and CCK8 (50 ng/kg/h) was started 30 min after injecting serum. Exogenous BPP (400 pmol/kg/h) was administered during the middle secretin/CCK hour. In a second protocol, 30 min after injecting nonimmune serum or PP-anti-serum, the animals were fed 15 g/kg cooked ground beef. Pretreatment with S5 enhanced secretin/CCK-induced bicarbonate outputs; protein outputs did not differ. Exogenous BPP inhibited pancreatic secretion, even in S5-treated animals. Meal-induced pancreatic secretion was not altered by S5 pretreatment. Significant increments in PP were measured by radioimmunoassay during administration of secretin/CCK and during BPP infusion. Anti-PP pretreatment abolished the former and significantly decreased, but did not abolish, the latter. The meal evoked significant postprandial increments in PP which were essentially abolished following S5 pretreatment. A physiological role for PP cannot be proved or refuted because antiserum pretreatment failed to block the effects of exogenous hormone. The latter must be established before excluding a peptide's physiological role based on negative in vivo immunoneutralization data.