The break‐down of [ 131 I]γ‐globulin in the digestive tract of the new‐born pig

1. The intestinal absorption of [ 131 I]porcine and bovine serum γ‐globulin after oral administration has been investigated in conscious pigs less than 20 hr old. Absorption was measured by the concentration of 131 I in venous blood during the 6 hr after feeding and also by the distribution of 131 I between homogenates of the alimentary tract and the rest of the animal at the end of the experiment. 2. The concentration of 131 I in the blood was always low after feeding [ 131 I]γ‐globulin, although a large proportion of the isotope fed was found to have left the alimentary tract. This indicated that much of the [ 131 I]‐γ‐globulin had been hydrolysed into fragments of low mol.wt. which were not retained in the plasma. There were no significant differences between results obtained with homologous and heterologous γ‐globulin. 3. Examination by gel‐filtration confirmed that, after feeding [ 131 I]‐serum γ‐globulin, much of the 131 I in the plasma was associated with material of mol.wt. less than 12,400 and demonstrated that the break‐down of bovine γ‐globulin was comparable with that of homologous γ‐globulin. 4. Comparison of the absorption of [ 131 I]serum γ‐globulin from colostrum with that from a chloride solution with a similar Na + and K + concentration showed that, although the blood concentration remained low, colostrum reduced the hydrolysis of the labelled protein. 5. This effect of colostrum could be simulated by the addition to the chloride solution of either the synthetic trypsin inhibitor Trasylol or a higher concentration of unlabelled protein. 6. Gel‐filtration of samples of the contents of the stomach, duodenum and terminal ileum after feeding [ 131 I]serum γ‐globulin showed that proteolysis occurred at all these sites.