Regulation of PSP/reg in rat pancreas:: Immediate and steady-state adaptation to different diets

Pancreatic stone protein/reg protein (PSP/reg) is a secretory pancreatic protein of hitherto unknown function. It is precursor to a spontaneously precipitating peptide called pancreatic thread protein, which is found in protein plugs within the pancreatic ductal system. Increasing PSP/reg concentrations in pancreatic juice might augment the risk of intraductal plug formation and therefore be a condition predisposing to chronic pancreatitis. Malnutrition is associated with a high incidence of chronic pancreatitis in tropical countries. In a diet study with rats, we tested the hypothesis that protein malnutrition leads to increased PSP/reg concentrations in pancreatic juice. A highly sensitive and reliable enzyme-linked immunosorbent assay (ELISA) for rat PSP/reg was newly established. Male Sprague-Dawley rats were allocated to three nearly isocaloric experimental diets, which contained 0, 45, or 82% casein, respectively, or to a control diet (22% casein). We evaluated PSP/reg expression under these four dietary conditions on the RNA and on the protein level, performing a time-course study over a period of 28 days. Our results demonstrate that PSP/reg expression is not increased because of a protein deficient diet if investigated under steady-state conditions. After a temporary increase in PSP/reg levels due to a carbohydrate-deficient high-protein diet, we could not find signs of a diet-dependent regulation of this protein. The regulation of PSP/reg thus differs from that of most other pancreatic secretory proteins. Our findings contradict earlier reports that had drawn conclusions based solely on messenger RNA levels.