Pancreatic Response and Plasma Secretin Concentration during Infusion of Low Dose Secretin in Man

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Abstract
Ten normal subjects were studied in order to estimate the sensitivity of the human pancreas to exogenous secretin and to investigate the relation between bicarbonate secretion and plasma secretin concentration. The duodenum was intubated and the fasting secretion of bicarbonate measured during gastric aspiration. Pancreatic secretion was thereafter stimulated by successively increasing doses of secretin given intravenously (0.01, 0.03, 0.1 and 0.3 clinical units × kg−1 × h−1). Concentration of secretin in infusates and in venous plasma was measured radioimmunochemically. The actual stimulation amounted to 85 per cent of the expected stimulation. The incremental plasma concentration of secretin correlated linearly to the actual stimulation, plasma secretin concentration (pmol Z l−1)=82 × secretin dose (C.U. × kg−1 × h−1) + 0.7, r = 0.915. The median metabolic clearance rate was 15.7 ml × kg−1 × min−1, and median half-life of exogenous secretin was 3.8 min. Physiological levels of secretin in plasma were obtained by secretin doses below 0.1 C.U. × kg−1 × h−1. Bicarbonate secretion and plasma secretin concentration were, even at the lowest stimulation level, significantly higher than basal values. Stimulated bicarbonate secretion was linearly correlated to log increment of secretin in venous plasma, bicarbonate output (mmol × h−1)=13.7 × log plasma secretin increment (pmol × l−1) + 0.7, r = 0.828.