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In agreement with what is known of pancreatic adaptation to dietary composition, a progressive lowering of amylase-to-chymotrypsinogen ratio was observed in the pancreases of rats fed mixed diets of increasing casein and decreasing carbohydrate contents. The same changes in ratio were found when casein alone was increased in otherwise isonitrogenous meals fed to rats provided ad libitum with a protein-free diet. Pancreatic accumulation of chymotrypsinogen was increased while that of amylase was decreased in spite of low-protein and high-carbohydrate intakes. Lowering the lipid content of the protein-free diet reduced the effectiveness of casein meals in lowering the amylase-to-chymotrypsinogen ratio. It is concluded that 1) the capacity of protein-rich diets to induce adaptative changes in pancreatic secretion does not depend on the absolute amount of proteins passing through the duodenum but rather on the increased protein concentration in the alimentary bolus, 2) protein concentration affects both amylase and chymotrypsinogen, and 3) lipids have a cooperative effect.

In virgin female rats thioacetamide administration (1 mg/100 g body wt) induced a 16-fold increase in liver ornithine decarboxylase (ODC) activity and a significant decrease (19%) in hepatic urea concentration. The ornithine-metabolizing enzymes, ornithine-oxo-acid aminotransferase and ornithine carbamoyltransferase, were not modified by the treatment; only carbamoyltransferase, were not modified by the treatment; only carbamoyl-phosphate synthetase I activity was significantly reduced. In 19-day pregnant rats DL-alpha-difluoromethylornithine treatment inhibited the expression of enhanced ODC activity occurring normally at this stage of pregnancy. Concomitantly an inhibition of the usual decrease in hepatic urea was observed. This increase of ureagenesis occurred without any increase in liver N-acetylglutamate or ornithine concentrations, which remained as low as in normal pregnant rats.

Liver ornithine decarboxylase (ODC) and tyrosine aminotransferase (TAT) activities were assessed at 2200 h (prandial phase) and at 1000 h (postprandial phase) in virgin and in pregnant (day 13-20) rats fed on different levels of casein and carbohydrate. In virgin rats, ODC levels were higher at 2200 h after resumption of eating than at 1000 hours, the inductive effect being greater with the high-casein than with the low-casein diet. Rapid deinduction followed termination of eating, resulting in equally low enzyme levels at 1000 h with both diets. On the contrary, prandial and postprandial levels of TAT were always greater with the high-protein diet. In pregnant rats, there was a progressive stimulation of ODC that reached a maximum on day 19. However, the inductive capacity of the high-protein diet was lower than that of the low-casein diet. Prandial rest was not followed by enzyme deinduction at 1000 h. In contrast, TAT stimulation remained dependent on overall casein ingestion. At constant casein but restricted carbohydrate intake, pregnant females exhibited a reduction in ODC stimulation. Thus, whereas in virgin females proteins are determinant in the regulation of ODC, during pregnancy there determinant in the regulation of ODC, during pregnancy there is a shift toward modulation by carbohydrates. Levels of liver urea and ornithine were found to vary in inverse proportion with the magnitude of ODC stimulation.

The participation of the liver to the increase in alanine utilization seen at midpregnancy was studied in 9- and 12-day pregnant rats. Liver fractional extraction of alanine was assessed in vivo from the changes in concentration in afferent and efferent vessels. Hepatic active transport of alanine was determined in vitro using isolated plasma-membrane vesicles. Compared with nonpregnant controls, alanine fractional extraction was significantly increased on day 12 but not on day 9 of pregnancy. Vesicles isolated from 9- and 12-day pregnant animals had a greater capacity for Na+-dependent transport than those from controls. Eadie-Hofstee plotting showed that this increase was due to an increase in Vmax with no change in Km. Both A and ASC systems contributed to the Vmax increase. These results indicate that, although by day 9 the liver has developed an increased capacity for alanine uptake, the actual extraction is seen only by day 12 of pregnancy. At this stage the liver participates actively in the turnover of alanine and the development of hypoalaninemia.