Norepinephrine stimulation of rat pineal type II thyroxine 5'-deiodinase

In the present paper we show, for the first time, an in vivo activation of rat pineal thyroxine 5'-deiodinase activity by injecting norepinephrine, the physiological neurotransmitter released by sympathetic nerve endings. In this work we performed the experiment injecting norepinephrine joined to DMI, which inhibits the norepinephrine uptake by the nerve terminals. Under these conditions norepinephrine exhibits a very potent effect in stimulating rat pineal thyroxine 5'-deiodinase activity. Moreover, the response to norepinephrine is greater in pineals collected from euthyroid animals, confirming that during hypothyroidism, pineal gland is supersensitive to adrenergic agonists probably due to the presence of larger quantities of mRNA for the synthesis of the enzyme.