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Effect of P₁-purinergic agonist on thyrotropin stimulation of H₂O₂ generation in FRTL-5 and porcine thyroid cells

Björkman U, Ekholm R. Effect of P₁-purinergic agonist on thyrotropin stimulation of H₂O₂ generation in FRTL-5 and porcine thyroid cells. Eur J Endocrinol 1994;130:180–6. ISSN 0804–4643

Our previous studies have shown that the generation of H₂O₂ in FRTL-5 thyroid cells is regulated via both the adenylate cyclase/cyclic adenosine monophosphate (cAMP) and Ca²⁺/phosphatidylinositol pathway: thyrotropin (TSH) stimulates H₂O₂ generation through both pathways, via the former at a low concentration and via the latter at a high concentration. In porcine thyrocytes in primary culture H₂O₂ generation is stimulated only via the Ca²⁺/phosphatidylinositol route. In the present study we explored the effect of a P₁-purinergic agonist (phenylisopropyladenosine, PIA) on stimulations induced by TSH and by adenosine triphosphate (ATP), an activator of the Ca²⁺/phosphatidylinositol cascade via the P₂-purinergic receptor. In FRTL- 5 cells, PIA potentiated H₂O₂ generation stimulated by TSH at 10U/l (but not at 1 U/l), Ca²⁺ mobilization induced by TSH and Ca²⁺ mobilization induced by ATP at 1 µmol/l (but not 10 µmol/l). Phenylisopropyladenosine strongly inhibited TSH-induced cAMP accumulation in FRTL-5 cells. In pig thyrocytes, PIA had no effect on H₂O₂ generation stimulated by TSH or ATP and no effect on ATP-stimulated Ca²⁺ mobilization. Also, PIA did not inhibit TSH-stimulated cAMP accumulation in pig thyrocytes, and by itselfhad no effecton H₂O₂ generation or Ca^{2 +} mobilization. Thus, in FRTL-5 cells, but not in porcine thyrocytes, PIA modulates TSH-stimulated H₂O₂ generation by enhancing the Ca²⁺/phosphatitylinositol route and inhibiting the adenylate cyclase/cAMP route of the TSH signal. The net result of this modulation apparently depends on the balance between inhibition of the cAMP route and enhancement of the Ca²⁺ route. This may explain the lack of potentiation observed by 1 U/1 TSH.

Ragnar Ekholm, Department of Anatomy, Medicinaregatan 3, S-413 90 Göteborg, Sweden

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