Influence of Fixatives on the Metachromatic Reaction to Toluidine Blue at pH 5; A1and A2Cells of Human Endocrine Pancreas

A comparison of the results obtained on the same section with toluidine blue at pH 5, and with silver impregnation according to Bodian and to Hellman-Hellerström, was made on the two categories of A cells in human islet tissue. Fixatives were: Bouin's, 10% neutral formol-saline, Baker's formol-Ca, and 6 or 12.5% glutaraldehyde in phosphate buffer at pH 7.2. Both 3-5 μ paraffin sections and 1 μ epoxy-resin sections were used. Staining by toluidine blue, 0.1–0.005% in Walpole's acetate buffer at pH 5, was performed with or without prior acid hydrolysis. In a population of A cells, those of A1 type are clearly distinguished by the silver impregnation of Hellman-Hellerström regardless of the fixative used. It can be noted with certainty that, in the human islet of Langerhans, with a fixative of the Bouin type, the metachromatic cells at pH 5 correspond uniquely to the A1 cells. However, when the fixative is an unmodified aldehyde both A1 and A2 cells show undifferentiated metachromasia at pH 5.