Different experimental conditions which regulate type II 5'-deiodinase mRNA in rat Harderian gland

In the present study, we describe the modifications in the expression of type II 5'deiodinase activity (5'D) in Xenopus laevis oocytes by injection of polyadenylated (poly A) mRNA from hypothyroid rat Harderian gland. The time-course study showed that the expression of the enzyme was dependent on time. Thus, enzyme activity was observed in oocytes 6 and 12 hours after the injection with poly A mRNA, reaching a maximal value at 24 hours. The activity was partially inhibited by 6-n-propyl-thiouracil, completely inhibited by iopanoic acid and exhibited a higher affinity for the T-4 (Km=1.5 nM) than rT(3) (Km=20 nM). The expression of the enzyme was modified in different experimental conditions: (a) exhibited diurnal variations with maximal peak values at night, (b) was inhibited by light at night and, (c) was activated by isoproterenol. On the other hand, we have also identified, for the first time, the size of mRNA capable of inducing 5'D in rats.