A possible indicator of urinary NH2-terminal big gastrin immunoreactivity for gastrin secretion

Urinary and plasma gastrin immunoreactivities in normal subjects were studied by radioimmunoassays using three region-specific antisera. Urinary excretion of NH2-terminal big gastrin immunoreactivity (NT G-34-IR) in the fasting state (0.79 +/- 0.17 pmol/kg/h, mean +/- SE) was several hundred times as much as that of either COOH-terminal gastrin or gastrin/cholecystokinin immunoreactivity. Urinary NT G-34-IR increased significantly after feeding, and correlated closely with integrated plasma NT G-34-IR. Renal clearance of NT G-34-IR was 62.4 +/- 7.9 ml/min and about one hundred times greater than that of any other gastrin immunoreactivities, indicating that there exist different catabolic pathways of gastrin peptides in the kidney. Gel filtration of urine extract revealed that a single giant peak of NT G-34-IR eluted in a later position than NH2-terminal heptadecapeptide of big gastrin. These results suggest that most of plasma NT G-34-IR is excreted in urine, and urinary excretion of NT G-34-IR reflects well-integrated plasma NT G-34-IR. Therefore, urinary NT G-34-IR may serve as a feasible indicator for gastrin secretion.