Response of well-fed adrenalectomized rats to tryptophan force-feeding on hepatic protein and RNA synthesis

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Response of well-fed adrenalectomized rats to a single tube-feeding of l-tryptophan over a period of 5 hr with respect to hepatic protein and RNA synthesis was investigated. Within 30 min of tryptophan force-feeding, the endogenous mRNA-directed ribosomal protein synthesis in a cell-free system and [ 14C]orotic acid incorporation into liver RNA in vivo were considerably increased as compared to the initial water-fed controls. However, the values returned essentially to the respective control level within the next 30 min and then increased again. Five hours after tryptophan administration, both in vitro protein and in vivo RNA synthesis were 26 and 27% higher, respectively, than that of the initial water-fed adrenalectomized control. At 30 min and 5 hr after tryptophan administration, the liver polyribosomes showed higher proportions of heavier aggregates as compared to the control. Nuclei isolated from the liver of adrenalectomized water-fed control and tryptophan-treated rats after different time periods were tested for both Mg 2+- and Mn 2+ (NH 4) 2SO 4 -dependent RNA polymerase activities. The activity of Mg 2+- and Mn 2+ (NH 4) 2SO 4 -dependent RNA polymerase was found to be significantly higher at 15 min and 5 hr after tryptophan administration when compared with the initial water-fed control.