Autoradiography of3H-α-Fluoromethyl Histidine in Mice: Correlation with the Kidney Histidine Decarboxylase Activity

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Abstract
Tritium‐α‐fluoromethyl histidine (3H‐α‐FMH), designed as a kcat‐inhibitor of mammalian histidine decarboxylase (EC 4.1.1.22), was administered intravenously in male and pregnant female mice of the NMRI strain and the distribution of tritium in the body recorded by whole‐body and microautoradiography. The results showed penetration of radioactivity into most tissues within 5 min. after the injection. After 4 hrs the highest levels of radioactivity were present in the intestinal content and in the kidneys. In the pregnant animal there was also a high labelling of the foetal tissues. When whole‐body sections were washed in TCA prior to the autoradiographic exposure to retain only protein‐bound radioactivity, a distinct labelling pattern was seen in the kidneys of the pregnant female mice but not in those of the male mice. Microautoradiography of the kidneys showed that the cells involved were located within the proximal convoluted tubuli. In several mouse strains, including the NMRI, the activity of kidney histidine decarboxylase is low in the males but high in females during a transient period of pregnancy. Incorporation of tritium into kidney protein after treatment with 3H‐α‐FMH, was correlated to a loss in histidine decarboxylase activity. The isotopic labelling was confined mainly to a component which cofractionated with histidine decarboxylase in polyacrylamidegel electrophoresis (PAGE) under non‐denaturing conditions. Our data indicate that the cells described above represent the location of kidney histidine decarboxylase.