Immunoreactive GRP.

Radioimmunoassay specific for GRP was developed using C-terminal specific anti-synthetic porcine GRP sera. Measurement of the porcine gastrointestine and brain tissue extracts with GRP and with bombesin radioimmunoassays indicates that the bombesin-like immunoreactivity found in the porcine tissues is attributable to GRP or GRP-like materials. GRP-like immunoreactivity in extracts of porcine gastrointestinal tissues and pancreas was shown, by gel filtration, to comprise mainly two components: the first-eluting component corresponding to synthetic GRP and the second-eluting one to synthetic GRP(14--27) in their elution volumes. An extract of the hypothalamus also contained two similar components, while extracts of the medulla oblongata and cerebral cortex contained mainly the second-eluting immunoreactivity. Immunostaining with anti-GRP sera revealed positive nerve fibers in the myenteric nerve plexus of the porcine duodenum and in intrapancreatic ganglia, but no immunoreactivity endocrine cells in the mucosa of the porcine stomach and intestine. The results gave support to GRP as a new brain-gut peptide and suggested physiological significant of GRP as a neurotransmitter or neuromodulator.