Evidence of the Presence of Thyroid Hormones in Achatina fulica Snails.

Danilo Lustrino,Jairo Pinheiro,Michelle P Marassi,Alba C.M Silva,Iracema G Araujo,Denise P Carvalho,Vinícius M Tunholi-Alves,Rosane N Castro,Victor M Tunholi

doi:10.1590/0001-3765201720160698

Abstract

The objective of this study was to identify thyroid hormones and to examine their putative site of synthesis in Achatina fulica snails. For this purpose, radioimmunoassays were performed for T3 and T4 before and after long starvation with or without hemolymph deproteinization. Sodium/iodide symporter activity in vivo was analyzed through 125I administration with and without KClO4 pretreatment. Only T4 was detected, and its concentration decreased due to starvation or deproteinization. However, high-performance liquid chromatography analysis also showed the presence of T2 and T3 apart from T4, but rT3 was not detected in the A. fulica hemolymph. The sodium/iodide symporter activity was greater in cerebral ganglia than digestive gland, but KClO4 treatment did not inhibit iodide uptake in any of the tissues analyzed. Altogether, our data confirm for the first time the presence of thyroid hormones in A. fulica snails and suggest their participation in the metabolism control in this species, although the putative site of hormone biosynthesis remains to be elucidated.

Highlights

In mammals, the thyroid gland is responsible for the biosynthesis and secretion of 3,3′,5,5′-tetraiodo-l-thyronine l-thyroxine (l-T4) and3,3′,5-triiodo-l-thyronine (l-T3), so-called thyroid hormones (THs)
The biosynthesis of T3 and T4 occurs through several steps that are dependent on thyroglobulin (TG) synthesis, iodide transport across basal membrane, iodide oxidation, tyrosyl iodination sites in TG and coupling of the iodotyrosines, a process catalyzed by the enzyme thyroperoxidase (TPO) (Larsen et al 1998)
Qualitative highperformance liquid chromatography (HPLC) analysis showed that T2, T3 and T4 were present in A. fulica hemolymph but not reverse T3 (Fig. 3)

Summary

Introduction

The thyroid gland is responsible for the biosynthesis and secretion of 3,3′,5,5′-tetraiodo-l-thyronine l-thyroxine (l-T4) and3,3′,5-triiodo-l-thyronine (l-T3), so-called thyroid hormones (THs). THs play an important role in the regulation of energy homeostasis by stimulating oxygen consumption and heat generation. They are important to the normal growth and development of the organism (Haber et al 1988, Gupta and Chakrabarty 1990). Tensen et al (1994) showed the presence of thyroid-stimulating hormone (TSH) receptors in the freshwater gastropod Lymnaea stagnalis and Heyland et al (2006) showed evidence of the endogenous synthesis of THs in the sea hare Aplysia californica, and of the gene that encodes a peroxidase (AcaTPO) that is similar to the TPO found in mammals. To our knowledge the presence of THs and the mechanisms of regulation and synthesis/metabolism of THs in land snails are still poorly unknown

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