Nitric oxide enhances thyroid peroxidase activity in primary human thyrocytes

Recent studies have demonstrated the production of the multi-functional messenger molecule nitric oxide (NO) by the thyroid gland. To examine a possible role for NO in thyroid function, we studied the acute and chronic effect of NO donors on thyroid peroxidase (TPO) activity in monolayer cultures of primary human thyrocytes, using a colorimerric assay technique. The presence of either S-nitrosoglutathione (GS-NO) or sodium nitroprusside (SNP) (10 −6–10 −4 M) at the time of the assay caused a significant increase in TPO activity. Pre-incubation of thyrocytes with 10 .5 M GS-NO for 3 days had no effect on the level of TPO activity when the assay was performed in the absence of NO donors. However, GS-NO pre-incubation significantly enhanced the acute stimulatory effect of GS-NO and SNP on TPO activity. These results suggest a possible role for NO in the regulation of TPO activity and thus thyroid hormone synthesis.