DDAH-1mRNA expression DDAH-1 mRNA expression was significantly decreased in the hypothalamus and in the medulla of rats treated with GTN when compared to CT group. No significant difference in DDAH-1 mRNA expression was found in the mesencephalon of rats treated with GTN when compared to CT group (Fig. 5). Fig. 5 DDAH-1 mRNA expression in specific brain areas, 4 h after glyceryl trinitrate (GTN) or vehicle (CT) administration. Data are expressed as mean ± SD, Mann Whitney test, *p <0.05 vs vehicle (CT)