Abstract
Three submicroscopic procedures for zinc-detection in β cells of the islets of Langerhans of adult pigs, rabbits and rats, were studied. In Procedure A (intra venous method with dithizone), portions of the pancreas were fixed in cold phosphatebuffered formaldehyde after an intravenous administration with dithizone and frozen sections of 40μ thickness were made. They were immersed in cold 1% silver nitrate solution with 5.7% sucrose for approximately 2 hours in a dark place. After washing, the tissues were cut into smaller pieces containing an islet using a stereomicroscope, followed by dehydration and embeddment into epoxy resin for electron microscopy. In Procedure B (modified Voigt's silver sulfide method) tiny pancreatic blocks were fixed in cold H2S-saturated 70% alcohol in a dark place for approximately 2 hours. They were dehydrated and embedded in epoxy resin. Ultrathin sections were treated with the reducting agents containing silver nitrate, and observed under an electron microscope. Procedure C (paraffin-embedding method) was performed as follows: pancreatic tissue portions were fixed in absolute alcohol, embedded in paraffin and cut at 40μ. The sections, stained with dithizone, were immersed into 1% silver nitrate solution and developed with the reducing agent. They were then dehydrated and embedded in epoxy resin.
The above procedures for detection of zinc in β cells were easily reproducible except in Procedure C, in which considerable amounts of reduced silver grains were extracted during dehydration. Procedure B is an application of Voigt's silver-sulfide method for light microscopy but proved disadvantageous in that the intracellular structures of β cells were markedly disintegrated. On the other hand, Procedure A showed the sites of zinc and the preservation of β cell ultrastructure most satisfactorily in the earliest period after dithizone injection.
The reaction products, which correspond to the submicroscopic localizing sites of zinc, were demonstrated mainly in mature granules and on their encasing membranous sacs. A small amount were also present occasionally in relation to the endoplasmic reticulum.
