Morphology and lectin-binding sites of pyloric caeca epithelium in normal and GnRH-treated Atlantic bluefin tuna (Thunnus thynnus) Linnaeus 1758.

Mucosal epithelium of pyloric caeca was studied in normal and in GnRH-treated Atlantic bluefin tuna Thunnus thynnus L., using morphological analysis, conventional and lectin glycohistochemistry. The lining epithelium consisted of columnar (absorptive) cells, goblet cells and intraepithelial leucocytes. The epithelium from normal animals was significantly taller than GnRH-treated samples. Conventional histochemistry displayed the same staining pattern in normal and hormone-treated specimens which showed a mixture of neutral and sulphated acidic glycoconjugates in the luminal surface and goblet cells, and neutral glycans in apical granules of enterocytes. Lectin histochemistry revealed a different glycoconjugate pattern in normal and GnRH-treated tunas. In normal specimens the luminal surface expressed sialoglycoconjugates which bound MAL II, SNA, KOH-sialidase-PNA, KOH-sialidase-SBA as well as asialoglycans stained with HPA, SBA, GSA I-B4 , LTA. N-linked glycans were highlighted by Con A and KOH-sialidase-WGA. In GnRH-treated tunas the luminal surface did not react with SNA, SBA and LTA. The columnar cells of normal tunas bound KOH-sialisase-PNA in the apical region, KOH-sialidase-PNA, KOH-sialidase-DBA, HPA, SBA, KOH-sialidase-SBA and KOH-sialidase-WGA in apical granules, GSA I-B₄ and LTA in the supranuclear region. GnRH-treated specimens showed some columnar cells that stained with KOH-sialidase-WGA in the apical granules and with GSA I-B4 in the supranuclear region. The goblet cells of normal animals produced mucins positive to PNA, HPA, KOH-sialidase-DBA, SBA, GSA II. The latter three binding sites lacked in GnRH-treated tunas. The results suggest that the mucosal epithelium of Thunnus thynnus L. pyloric caeca expresses a complex glycan pattern that is affected by GnRH-treatment.