Chromogranin A (CgA), a neuroendocrine pro-hormone, undergoes proteolytic cleavage to yield bioactive peptides, notably catestatin (CST) and pancreastatin (PST), which exert opposing effects on metabolic and inflammatory processes. Using CgA and CST knockout (KO) mice, this study investigated their roles in pancreatic endocrine function, morphology, neurotransmitter dynamics, and systemic glucose homeostasis. CST deficiency induced insulin resistance, altered islet architecture, and heightened catecholamine levels, whereas CgA-KO mice lacking both CST and PST exhibited improved insulin sensitivity due to absence of PST. CST suppressed gluconeogenesis and enhanced glucagon regulation, while PST promoted insulin resistance and glucose production. Spatial mass spectrometry revealed altered neurotransmitter and polyamine profiles in pancreatic islets, implicating disrupted nerve-immune-islet interactions. CST's modulation of catecholaminergic and inflammatory pathways positions it as a key regulator in the neuro-immune-endocrine axis. These findings highlight the therapeutic potential of targeting CgA-derived peptides, especially CST, for managing diabetes and metabolic-inflammatory diseases through precise peptide-based interventions.