Interleukin-1β inhibits rat thyroid cell function in vivo and in vitro by an NO-independent mechanism and induces hypothyroidism and accelerated thyroiditis in diabetes-prone BB rats

Interleukin-1β has been implicated as a pathogenic factor in the development of autoimmune thyroiditis. When given for 5 days to normal non-diabetes-prone Wistar Kyoto rats, it decreased plasma concentrations of total tri-iodothyronine and thyroxine and increased plasma TSH. These effects were not prevented by co-injection of nitroarginine methyl ester or aminoguanidine, inhibitors of NO synthases. Exposure to interleukin-1β dose-dependently reduced iodine uptake in FRTL-5 cells, but had no effect on thyroglobulin secretion. Nitrite was not detected in the FRTL-5 cell culture media after exposure to interleukin-1β. However, reverse transcription PCR analysis of mRNA isolated from interleukin-1β-exposed FRTL-5 cells revealed a transitory expression of the inducible NO synthase, which was markedly lower than inducible NO synthase induction in interleukin-1β-exposed isolated rat islets of Langerhans. Co-incubation with the NO synthase inhibitor N G -monomethylarginine did not ameliorate the effect of interleukin-1β on FRTL-5 cell iodine uptake. Furthermore, we demonstrate that daily injections of interleukin-1β for 13 weeks aggravated spontaneous thyroiditis and induced severe hypothyroidism in non-diabetic diabetes-prone BB rats. The data suggest that NO does not mediate interleukin-1β-induced inhibition of rat thyroid function in vivo or in vitro in FRTL-5 cells, and the induction of hypothyroidism by interleukin-1β in diabetes-prone BB rats is speculated to be due to exacerbation of recruitment and activation of intrathyroidal mononuclear cells.