Selective staining and disintegration of intestinal eosinophilic granule cells in Atlantic salmon after intraperitoneal injection of the zinc chelator dithizone

Following intraperitoneal injection of the zinc ion chelator dithizone into Atlantic salmon Salmo salar. staining and morphological changes in intesti nal eosinophiic granule cells (EGC) were observed in both cryo-preserved an d chemical-preserved tissue sections. In cryo sections rapid and selective vital staining of EGC was observed within 5 min of dithizone injection. Int ensely stained red granules appeared as a result of the formation of a comp lex between dithizone and zinc ions. Stained EGC appeared on both sides of the stratum compactum as well as in the lamina propria. Stained EGC started to disintegrate 5 min after the injection of dithizone, and little of the zinc-dithizone complex was observed 15 h later. The disappearance of the st ain coincided with an intense degranulation and disintegration of EGG. Fift een hours after dithizone treatment regenerating cells were observed in Mas son's trichrome stained sections. Four to five days after injection, a full y regenerated continuous EGC layer was observed. Simultaneously with the di sintegration of EGC an increase in plasma lysozyme activity occurred. EGC r esembles mammalian Paneth cells in their possession of lysozyme-containing granules and their staining by, and response to, dithizone. EGC may represe nt a central component of zinc metabolism in Atlantic salmon. (C) 2001 The Fisheries Society of the British Isles.