INFLUENCE OF THE THYROID-HORMONE STATUS ON TYROSINE-HYDROXYLASE IN CENTRAL AND PERIPHERAL CATECHOLAMINERGIC STRUCTURES

We investigated the effect of hyper- and hypothyroidism on tyrosine hy droxylase protein concentration in the locus coeruleus (divided into a nterior and posterior parts), the substantia nigra and the adrenals of adult rats. Rats were made hypothyroid with propylthiouracile (PTU, 0 .02% in drinking water for 21 days) or hyperthyroid by thyroxine injec tion (100 or 250 mu g/kg/day), for 3 or 17 days. PTU treatment resulte d in a statistically significant decrease of tyrosine hydroxylase in t he anterior locus coeruleus (-13%) and the adrenals (-14%). After thyr oxine treatment, in the anterior locus coeruleus, tyrosine hpdroxylase was significantly higher (2 way ANOVA) after the 3 day treatment than after the 17 day treatment: tyrosine hydroxylase showed a trend to in crease after the 3 day treatment (+20% with the 250 mu g/kg dose) and to decrease after the 17 day treatment (-15% with the 250 mu g/kg dose ). In the adrenals, tyrosine hydroxylase was increased by the 3 day tr eatment (+42% after the 250 mu g/kg dose), but this increase was not o bserved after 17 days of treatment. Tyrosine hpdroxylase was not alter ed in the posterior locus coeruleus and the substantia nigra, whatever the treatment. Together, our results support the hypothesis that in t he anterior locus coeruleus and in the adrenals tyrosine hydroxylase l evel is positively modulated by thyroid hormones. After long-term trea tment (17 days) this effect is not observed.