Effects of Fasting and Subsequent Feeding of a Complete or Tryptophan-Free Diet on the Activity of DNA-Synthesizing Enzymes and Protein Synthesis in Gastric Mucosa of Rats

Abstract

Effects of fasting for 1–4 days and subsequent feeding of 4-day fasted rats with a complete or tryptophan-free liquid diet (40 kcal/day) for 1–4 days on the activity of thymidine kinase and DNA polymerase and protein synthesis were investigated in gastric mucosa. Rats maintained on ad libitum chow pellets served as control. Starvation for 1–4 days diminished gastric mucosal thymidine kinase and DNA polymerase activities, which attained their respective lowest levels of 53 and 65% of the fed control (chow-fed) after 2 days. Refeeding the complete diet for 1 day increased thymidine kinase activity to 87% of the fed control; it increased slightly thereafter. The tryptophan-free diet was ineffective in stimulating gastric mucosal thymidine kinase for up to 3 days, but after 4 days on the diet the enzyme activity was increased to 78% of the fed control level. On the other hand, DNA polymerase activity began to increase after 1 day on the tryptophan-free diet and reached the fed control level after 4 days. The complete diet caused an initial reduction (for up to 2 days) in DNA polymerase activity, but after 3 days it rose to the level of the fed control. The ability of gastric mucosal polyribosomes to synthesize endogenous mRNA-directed protein in a cell-free system was decreased by 44 % after 4 days of fasting. Whereas refeeding of the complete diet for 4 days enhanced protein synthesis to 75 % of the fed control level, the tryptophan-free diet was found to be ineffective. The protein to polyphenylalanine ratio, which represents a ratio of poly-somes to monosomes, was also decreased by 42% after 4 days of fasting, but could be returned to the fed control level by the complete diet and not by the tryptophan-free diet. It is concluded that the presence of tryptophan in the dietary mixture is important for initiation of cellular proliferative activity and for resumption of protein synthesis in the gastric mucosa of fasted rats.

Effect of Benzodiazepines on Tryptophan Binding to Rat Hepatic Nuclei

“…In searching for other references to the relation between binding sites for L-tryptophan and benzodiazepines in other systems, we found that KraghHansen (19,20) (11,16,25). Also, we have reported that rat brain nuclei contain tryptophan-binding receptors (6).…”