Identification and localization of glucagon-related peptides in rat brain.

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Abstract
Immunochemical and immunocytochemical techniques were used to identify and characterize glucagon-related peptides of the rat CNS. These peptides show immunoreactivity with antiglucagon sera directed towards the central portion of the hormone, but not with antisera specific for the free COOH terminus of glucagon. Highest concentrations were found in hypothalamus (6.1 .+-. 1.6 ng/g wet wt) although lower amounts (.apprx. 2 ng/g) were found in cortex, thalamus, cerebellum and brain stem. Gel filtration of brain extracts revealed at least 2 immunoreactive forms, which have MW of .apprx. 12,000 and 8000. Both peptides had radioimmunoassay dilution curves parallel to the curve for glucagon and both had identical counterparts in extracts of rat intesinte. Digestion of the brain and intestinal peptides with trypsin plus carboxypeptidase B released the immunoreactive COOH-terminal tryptic fragment of pancreatic glucagon from these larger forms. Immunocytochemical studies using antiglucagon serum and peroxidase-antiperoxidase staining identified glucagon-like material in neuronal cell bodies and processes in the magnocellular portion of the paraventricular nucleus, in scattered cells in the supraoptic nucleus and in fibers in the median eminence. Glucagon-containing peptides that have undergone the intestinal type of posttranslational modification apparently are present in neuronal cells of the rat hypothalamus.