Conversion of [4,5-3H] leucine into 3H2O and tritiated metabolites in rat brain tissue. Comparison of a peripheral and intracranial route of administration

Polyneuropathies and CNS Protein Metabolism. Ii. Changes in the Incorporation Rate of Leucine During Acrylamide Intoxication

“…The in uiuo incorporation rates of leucine into proteins of the spinal cord, of brain stem and of heart muscle were measured using a pulse of tritiated leucine by intraperitoneal injection after which a rather uniform labelling would be expected throughout the organism (Figure 1, Table 1) (Rees, Brogan, Entingh, Dunn, Shinkman, Damstra-Entingh, Wilson & Glassman, 1974). A relatively short incorporation period (20 min) was chosen for two reasons: (a) uptake and metabolism of the radioactive precursor in the tissue was fast (Schotman, Gispen, Jansz & De Wied, 1972;Schotman, Gipon & Gispen, 1974) and (b) incorporation was taken as measure of synthesis rather than turn-over rate of proteins. The incorporation into proteins was expressed as per cent of total radioactivity.…”

H‐Pro‐[3H]Leu‐Gly‐NH2: Plasma Profile and Brain Uptake Following Subcutaneous Injection in the Rat

“…The observed incorporation of radioactivity into TCA-insoluble proteins and the transfer of label to tritiated water are well-known phenomena in in vivo fate studies of labeled peptides and amino acids (Schotman et al, 1974;Verhoef and Witter, 1976;de Wildt et al, 1982). The metabolite profiles in rat plasma and brain tissue obtained after S.C. administration of [3H]PLG, with respect to both the presence of [3H]leucine as the major radioactively labeled metabolite and the finding of [3H]Leu-Gly-NH, as the sole labeled peptide intermediate in only trace amounts, are in accordance with those obtained after in vitro incubations of PLG with plasmaherurn (Walter et al, 1975;Witter et al, 1980) or brain subcellular preparations (Marks et al, 1974;Hui et al, 1980;de Wildt et al, 1982), as well as to those found after i.v.…”

Postnatal Increase in the Metabolism of Leucine and Valine

“…Furthermore, metabolic inhibitors (anesthetics and sublethal amounts of cya nide) inhibited 3H20 formation, which is consistent with a depression of leucine me tabolism. Thus, the large proportion of la beled w'ater appearing in the adult rat imme diately following a pulse of tritiated leucine, administered subcutaneously [9,18], intrave nously [1], or intraperitoneally (as reported here), results from enzyme catalyzed reac tions.…”

“…Although leucine administered by an intraperitoneal route is rapidly degraded, any leucine transported into the brain [12,16] is primarily synthesized into protein [11,15,16,24]. Similarly, there is relatively little catabolism of leucine administered directly into the brain by injection [18].…”

“…While the intraperitoneal administration of leucine labels protein in different brain regions more uniformly than by intracranial administra tion [23], one disadvantage is the catabolic loss of administered leucine prior to active transport into the brain. Several investiga tions have previously shown that within min utes following the intravenous [2] or subcuta neous [18] injection of tritiated leucine or valine into adult rats half or more of the brain acid-soluble radioactivity exists in the form of tritiated water (3H20). The present experiments were undertaken to investigate this phenomenon, and our results indicate a major increase in catabolism of the branched-chain amino acids during late post natal development in the rat.…”