Leptin and ghrelin concentration in hyperthyroid cats before and after radioactive iodine therapy compared to euthyroid control cats^[*]

Summary

Objective: Leptin and ghrelin, two peptide hormones with antagonistic effects on satiety and energy balance, could be involved in the pathogenesis of weight loss and polyphagia in cats with hyperthyroidism. Leptin generally decreases appetite and increases energy expenditure, while ghrelin exerts the opposite effects. Materials and methods: Leptin and ghrelin were measured in 42 client owned hyperthyroid cats with a body condition score (BCS) 5/9 before (T0) and 4 weeks after radioactive iodine treatment (RAIT) (T1). Dependent on the serum total thyroxine concentration concentration at T1, cats were sub-classified as still hyperthyroid (ht-ht) (n = 4), euthyroid (ht-eu) (n = 10) or hypothyroid (ht-hypo) (n = 28). Results were compared to those of 22 healthy, euthyroid control cats with a comparable BCS ( 5/9) and age ( 8 years) to hyperthyroid cats. Results: At T0, there were no significant differences between hyperthyroid and control cats for leptin (p = 0.06) or ghrelin concentrations (p = 0.27). At T1, leptin significantly decreased in ht-hypo cats compared to T0 (p = 0.0008) despite a significantly increased body weight in this group (p = 0.0001). Serum ghrelin concentrations did not differ between hyperthyroid cats with a history of polyphagia compared to non-polyphagic cats (p = 0.42). After RAIT, ghrelin concentration significantly increased in all hyperthyroid cats (p < 0.0001), as well as in the subgroups ht-eu (p = 0.014) and ht-hypo (p < 0.0001) compared to their respective T0 baseline concentrations. Conclusion: Leptin and ghrelin fluctuations may be indicative of changes in metabolic functions in cats with thyroid dysfunction. Leptin fluctuations occurred independently of body weight in different states of thyroid dysfunction; increasing ghrelin concentrations after RAIT suggest a ghrelin-independent mechanism for polyphagia in hyperthyroid cats.

Zusammenfassung

Gegenstand und Ziel: Leptin und Ghrelin, zwei Peptidhormone mit antago nistischem Effekt auf Sättigung und Energiebilanz, könnten bei Katzen mit Hyperthyreose in die Pathogenese von Gewichtsverlust und Polyphagie involviert sein. Leptin führt allgemein zu vermindertem Appetit und erhöhtem Energieverbrauch, Ghrelin bewirkt entgegengesetzte Effekte. Material und Methoden: Bei 42 Katzen mit spontan auftretender Hyperthyreose und einem Body Condition Score (BCS) 5/9 wurden Leptin und Ghrelin vor (T0) und nach Radioiodtherapie (RAIT) (T1) bestimmt. Abhängig von der Gesamt-T4-Konzentration zum Zeitpunkt T1 erfolgte eine Subklassifizierung der Tiere als weiterhin hyperthyreot (ht-ht) (n = 4), euthyreot (ht-eu) (n = 10) oder hypothyreot (ht-hypo) (n = 28). Die Resultate wurden mit denen 22 gesunder, euthyreoter Katzen mit ähnlichem BCS ( 5/9) and Alter ( 8 Jahre) ver glichen. Ergebnisse: Zum Zeitpunkt T0 ergaben sich bei hyperthyreo ten und Kontrollkatzen keine signifikanten Unterschiede hinsichtlich der Leptin- (p = 0,06) oder Ghrelinkonzentration (p = 0,27). Die Leptinkonzentration der Gruppe ht-hypo war an T1 signifikant niedriger als an T0 (p = 0,0008), trotz eines signifikant höhe ren Körpergewichts (p = 0,0001). Die Ghrelinkonzentrationen von Katzen mit und ohne Polyphagie differierten nicht signifikant (p = 0,42). Nach RAIT stieg die Ghrelinkonzentration signifikant in der gesamten Gruppe zuvor hyperthyreoter Katzen (p < 0,0001) sowie in den Subgruppen ht-eu (p = 0,014) und ht-hypo (p < 0,0001) im Ver gleich zu T0. Schlussfolgerung: Fluktuationen der Leptin- und Ghrelinkonzentration könnten bei Katzen mit Schilddrüsendysfunktion auf metabolische Veränderun gen hindeuten. In verschiedenen Phasen der Schilddrüsendysfunktion zeigten sich Fluktuationen der Leptinkonzentration unabhängig vom Körpergewicht. Erhöhte Ghrelinkonzentrationen nach RAIT deuten auf einen ghrelinunabhängigen Mechanismus für Polyphagie hin.

Keywords

Thyroid dysfunction - thyroid hormones - feline

Schlüsselwörter

Schilddrüsendysfunktion - Schilddrüsenhormone - Katze

^* Presented in abstract form at the 22. Annual Meeting of the Professional Group of Internal Medicine and Clinical Pathology of the German Veterinary Society, Giessen, Germany, February 2014. Data from this study were presented as a poster at the ACVIM Forum, June 4–7, 2014, Nashville, TN, USA.

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