AbstractIn order to determine whether the uptake of gastrin and secretin is limited to specific organ systems (especially the kidney) or whether loss is a nonspecific occurrence across all capillary beds, we have measured the uptake of endogenous and exogenous gastrin and secretin in 32 anesthetized dogs. In 6 dogs, antral irrigation with 0.5% acetylcholine solution produced a brisk increase in gastrin concentrations measured in blood from the aorta. Concentrations in blood from the renal, jugular, and femoral veins were all significantly lower, and there was an integrated uptake of gastrin of 48% by the kidney, 43% by the hind leg, and 36% by the head (the differences were not significant from one another). Exogenous infusion of synthetic human gastrin in 6 dogs at 2 dose levels (0.4μg/kg‐h and 0.8μg/kg‐h) caused a rise in aortic blood concentration of gastrin with significantly lower levels in blood from the renal, femoral, and jugular veins. Calculated as integrated gastrins, the kidney removed 42%, the hind leg 35%, and the head 30% of gastrin at 0.8/μg/kg‐h. Similar percentages were extracted at the lower dose. In 5 dogs, endogenous release of secretin was secured by duodenal irrigation with 0.1 N HCl. This brought about an elevation in the aortic blood concentration of secretin from a basal level of around 60 pg/ml to 217 ±24 pg/ml at 45 minutes. Secretin concentrations in blood from the renal, femoral, and jugular veins were significantly lower, and the kidney removed 39%, the leg 29%, and the head 32% of integrated endogenously released secretin. There was no difference between the 3 sites. During infusion of exogenous secretin at 0.4 U/kg‐h, mean aortic blood levels ranged between 340–420 pg/ml, and levels in the blood from the renal, femoral, and jugular veins ranged between 220–295 pg/ml. When integrated secretin values were determined, the kidney was found to remove 42%, the hind leg 43%, and the head 43%. When secretin was given at 1 U/kg‐h, the kidney removed 46%, the hind leg 31%, and the head 26%. We conclude that extraction of gastrin and secretin occurs on transit of all capillary beds and appears to be a nonspecific process.