Characterization of L-Tryptophan Transport into Liver in Suckling Rats
In adult rats, about 10% of total plasma L-tryptophan (Trp) (ca. 100 μM) exists in a free form (not albumin-bound) under physiological conditions (Madras et al., 1974). We have demonstrated that Trp uptake into adult rat hep-atocytes occurs mainly via a trypsin-sensitive high-affinity transport component (Km – 14 μM) under physiological conditions (Saito et al., 1986). We have also shown that Trp uptake into adult rat hepatocytes via the high-affinity transport component is closely related to liver tryptophan 2,3-dioxy-genase (TPO) activity (Saito et al., 1987). However, rat liver TPO activity is known to appear rapidly about two weeks after birth (Franz and Knox, 1967). In addition, the proportion of free Trp, which can be utilized readily in tissues, in the plasma of suckling rats has been shown to be high compared to that of young and adult rats (Sarna et al., 1970). Taking these findings into account, it is suggested that Trp transport into suckling rat liver is different from that into young and adult rat liver. In order to elucidate the characteristics of Trp transport into suckling rat liver, we have examined the changes of liver TPO activity and Trp levels not only in serum and liver but also brain and muscle during development, using male rats aged 10 to 42 days. We also compared the mode of Trp uptake into hepatocytes between suckling and adult rats using isolated hepatocytes.
KeywordsHigh Performance Liquid Chromato High Performance Liquid Chromato Liver Tryptophan Fresh Liver Homogenate High Performance Liquid Chromato Method
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- Saito, K., Sasaki, E., Ohta, Y., Nagamura, Y., and Ishiguro, I., 1987, The effect of tryptophan 2,3-dioxygenase on L-tryptophan transport into rat liver, Seikagaku, 59: 732.Google Scholar