Abstract
Human urinary trypsin inhibitor (UTI) is the functional domain of serum inter-α-trypsin inhibitor. Rat urine also contains UTI-like immunoreactivity. To clarify the source of rat UTI, we performed a combination of reverse transcription-polymerase chain reaction (RTPCR), in situ hybridization and immunohistochemistry. The expression of UTI mRNA was detected by RT-PCR only in the liver and not in any other rat organs, including the kidney. In situ hybridization revealed that UTI transcripts are located exclusively in the hepatocytes and not in the nonparenchymal cells of the liver. On light microscopic immunohistochemistry, not only the hepatocytes but also the Kupffer cells of liver and the proximal tubules of kidney were immunostained with anti-UTI antibody. Immunoelectron microscopy further demonstrated that hepatocyte UTI-immunoreactivity is localized primarily on the cell surface facing the sinusoidal capillary and is also found in the Golgi apparatus. In contrast, the reactivity of Kupffer cell and proximal tubular epithelial cell was found primarily in the lysosomes. These results indicated that the liver is the only site for production of rat UTI, and that the kidney does not produce rat UTI but reabsorbs it from the primary urine.
