A histochemical study on the expression and localization of growth factors

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We have used both immunohistochemistry and in situ hybridization techniques to determine the sites of localization of immunoreactivity and mRNA signal of various growth factors in the entire rat body, and have obtained the following results :The expression of hepatocyte growth factor (HGF) was demonstrated in the submandibular gland of rats. Both the mRNA signal and immunoreactivity for HGF were localized to the epithelial cells of granular convoluted tubules. This finding added HGF to the list of many growth factors produced in the rodent submandibular gland.As an attempt for the electron microscopic in situ hybridization, the cryostat sections of rat submandibular gland were first treated for in situ hybridization with ^<35>S-labelled EGF probe and then embedded in epoxy resin for electron microscopic radioautography. The result suggested that this method is more useful for identifying morphologically the type of mRNA-positive cells than determining the subcellular localization of mRNA.An immunohistochemical study using an antibody against acidic fibroblast growth factor (aFGF) revealed that subpopulations of endocrine cells in the pancreas and small intestinal mucosa are positively immunostained in their secretory granules. This result suggested that an aFGF-like substance is produced by the cell populations that express glucagon-precursor.The expression of vascular endothelial growth factor (VEGF) is very low in the normal rat submandibular gland. However, a stimulation of submandibular gland to grow by isoproterenol caused a transient rise in the rate of expression of VEGF in this organ that peaked at 1 h after the stimulation. The mRNA was localized to the acinar cells. This result suggested a certain relation between isoproterenol-induced growth of submandibular gland and VEGF effects on the blood vessels.