Immunocytochemical identification of islet cells and nerve fibers containing calcitonin gene-related peptide-like immunoreactivity in the rat pancreas.

Calcitonin gene-related peptide-like immunoreactivity has been localized in endocrinelike or paracrinelike cells and nerve fibers of the rat pancreas. Immunoreactive cells with short and thick, elongated processes were mainly distributed at the periphery of the islets of Langerhans and occasionally disseminated among the acini. Positive varicose fibers were observed in both the endocrine and exocrine parenchyma as well as around blood vessels. Treatment with the small-diameter sensory fiber neurotoxin capsaicin resulted in virtually complete elimination of calcitonin gene-related peptide immunoreactive fibers innervating the parenchyma and blood vessels, suggesting an extrinsic, sensory origin of these fibers. The sympathetic neurotoxin 6-hydroxydopamine did not affect the immunoreactive staining. The results of this study support the possibility that a distinct cell population within the endocrine pancreas of the rat contains calcitonin gene-related peptide, and that this peptide plays both an endocrine/paracrine role, as well as a modulator role in the regulation of pancreatic function.