Influence of the thyroid hormone status on tyrosie hydroxylase in central and peripheral catecholaminergic structures

Abstract

We investigated the effect of hyper- and hypothyroidism on tyrosine hydroxylase protein concentration in the locus coeruleus (divided into anterior and posterior parts), the substantia nigra and the adrenals of adult rats. Rats were made hypothyroid with propylthiouracile (PTU), 0.02% in drinkin water for 21 days) or hyperthyroid by thyroxine injection (100 or 250 μg/kg/day), for 3 or 17 days. PTU treatment resulted in a statistically significant decrease of tyrosine hydroxylase in the anterior locus coeruleus (−13%) and the adrenals (−14%). After thyroxine treatment, in the anterior locus coeruleus, tyrosine hydroxylase was significantly higher (2 way ANOVA) after the 3 day treatment than after the 17 day treatment: tyrosine hydroxylase showed a trend to increase after the 3 day treatment (+20% with the 250 μg/kg dose) and to decrease after the 17 day treatment (−15% with the 250 μg/kg dose). In the adrenals, tyrosine hydroxylase was increased by the 3 day treatment (+42% after the 250 μg/kg dose), but this increase was not observed after 17 days of treatment. Tyrosine hydroxylase was not altered in the posterior locus coeruleus and the substantia nigra, whatever the treatment. Together, our results support the hypothesis that in the anterior locus coeruleus and in the adrenals tyrosine hydroxylase level is positively modulated by thyroid hormones. After long-term treatment (17 days) this effect is not observed.