PANCREASTATIN AND BOVINE PARATHYROID CELL SECRETION

Chromogranin A (CgA) is an acidic glycoprotein found in secretory granules of multiple peptidergic tissues and cosecreted with the resident peptide hormones. Pancreastatin is an amidated, biologically active peptide whose sequence is contained within CgA. We investigated the effect of the C-terminal fragment of bovine pancreastatin (bP32-47) on bovine parathyroid cell secretion. bP32-47 amide inhibited low-calcium-stimulated PTH secretion by 44% and chromogranin A (CgA) secretion by 33%. We were able to identify a pancreastatin-like peptide as a very minor component of the endogenous breakdown peptides from CgA. However, using several approaches, we were unable to detect pancreastatin in secretory granule extracts or in incubation media. We conclude that although exogenous bovine pancreastatin has inhibitory effects on secretion, detectable pancreastatin is not secreted under normal incubation conditions. Based on our current data, we would question the physiologic importance of pancreastatin in bovine parathyroid glands.