PROTEOLYTIC ACTIVITY DURING ABSORPTION OF [131I]GAMMA-GLOBULIN IN NEW-BORN CALF

1. Proteolytic activity within the small intestine of unsuckled calves less than 20 hr of age, anaesthetized with sodium pentobarbitone, has been assessed from the break‐down of [131I]bovine serum γ‐globulin infused into the duodenum. 2. Absorption of [131I]γ‐globulin was measured by analysis of venous blood, the levels of radioactivity attained in which were comparable with those when [131I]PVP K.60 (mean mol.wt. 160,000) was administered. When lymph collected from the thoracic duct during the absorption of [131I]γ‐globulin was injected into the femoral vein, the levels of radioactivity in the blood were close to those expected if the labelled material in the lymph had been retained within the plasma. These observations suggested that [131I]γ‐globulin was absorbed into the circulation of the anaesthetized young calf without significant break‐down. 3. Gel‐filtration of lymph and plasma from calves fed [131I]γ‐globulin has confirmed that proteolysis before and during absorption was slight, since little 131I labelled material of low mol.wt. was found. 4. Gel‐filtration of the contents of the alimentary tract from calves fed [131I]γ‐globulin showed that some hydrolysis occurred in the abomasum and duodenum and that this was reduced by barbiturate anaesthesia. Protein break‐down in the terminal ileum was slight both in the conscious animal and in animals anaesthetized with sodium pentobarbitone. © 1969 The Physiological Society