Molecular and morphological analysis on the mechanism of regulation by the relation of steroid metabolism between stomach and liver in the body.

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Although the stomach is regarded as an organ of the digestive tract, we have discovered that the parietal cells, which are known as oxyntic cells, in the rat gastric mucosa produce a large quantity of estrogen that is then secreted to portal vessels. We already confirmed that both the protein and mRNA of aromatase, estrogen synthetase, and its high enzymatic activity in the parietal cells by several techniques including immunohistochemistry, electron microscopy, in situ hybridization, RT-PCR, thin layer chromatography, GC-MS method. The mRNAs of several steroid-metabolizing enzymes were examined in the gastric parietal cells of adult male rats. These cells showed mainly the mRNA of P450_<17α>, 17β-HSD type III and P450_<arom>, although the mRNA of 17β-HSD type II, 5α-reductase type I and 3α-HSD was weakly expressed and none of P450_<scc>, 3β-HSD, P450_<c21>, P450_<11β> and P450_<AS> was expressed. The arterial concentration of progesterone and testosterone was high, and this suggests that the gastric parietal cells in rats can produce and secrete 17β-estradiol and estrone through progesterone or testosterone/androstenedione in the arterial blood. The developmental profiles of aromatase expression in rat gastric parietal cells were examined, and the enzyme expression begins soon after sucking. We are now examining a possibility that in the primate stomach another steroidogenic pathway may exist by the species difference in the expression of the enzymes.