Short-term regulation of tyrosine hydroxylase activity and expression by endothelin-1 and endothelin-3 in the rat posterior hypothalamus.

Brain catecholamines are involved in several biological functions regulated by the hypothalamus. We have previously reported that endothelin-1 and -3 (ET-1 and ET-3) modulate norepinephrine release in the anterior and posterior hypothalamus. As tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis, the aim of the present work was to investigate the effects of ET-1 and ET-3 on TH activity, total enzyme level and the phosphorylated forms of TH in the rat posterior hypothalamus.

Involvement of nitric oxide pathways in short term modulation of tyrosine hydroxylase activity by endothelins 1 and 3 in the rat anterior hypothalamus.

The ability of endothelins 1 and 3 (ET-1 and ET-3) to reduce neuronal norepinephrine release through ETB receptor activation involving nitric oxide (NO) pathways in the rat anterior hypothalamus region (AHR) was previously reported. In the present work, we studied the effects of ET-1 and -3 on tyrosine hydroxylase (TH) activity and the possible involvement of NO pathways. Results showed that ET-1 and -3 (10 nM) diminished TH activity in AHR and this effect was blocked by a selective ETB receptor antagonist (100 nM BQ-788), but not by a ET(A) receptor antagonist (BQ-610).