The ammocoetes endostyle: its oxidative enzymes as an evidence of its homology with the thyroid of higher chordates.

Histochemical methods were used for the demonstration of activity of the following intracellular oxidative enzymes, unstudied hitherto, in the epithelial cells of the endostyle of the river lampre (Lampertr aluviatilis L.) ammocoetes: reduced NAD dehydrogenase (NADD), lactate dehydrogenase (LD), cytochrome oxidase (CO), succinate dehydrogenase (SD), alpha-glycerophosphate dehydrogenase (alphaGPD) and glucose-6-phosphate dehydrogenase (G6PD). The activities of NADD and LD in the iodophil and throidogenic cells of type 3, then of subtype 2c and partly types 4 and 5 of the endostylar epithelium and the hypobranchial duct-lining epithelium were particularly ithe larva proves the possibility of their participation in the formation of the thyroid gland in the period of metamorphosis. In type 1 cells of the ammocoetes, despite their fairly strong enzymatic reactivity, the oxidative activity does not change significantly during the ontogenetic stages examined. The data obtained make it possible to modify the present views on the genesis of the thyroid gland of the adult lamprey, namely, they indicate the participation of the type 6 cells of the hypobranchial duct-lining epithelium in the process of thyroidogenesis.