title: Seasonal changes of the 5'-monodeiodination activity in kidney and skin homogenates of male Rana ridibunda: relation to plasma thyroxine (T4) and testosterone.
abstract: Plasma concentrations of thyroxine (T4) and testosterone were studied together with the in vitro 5'-monodeiodination activity in liver, kidney, and skin homogenates in male Rana ridibunda during 12 consecutive months. Plasma T4 levels increase in February, drop in April, and increase again in May. In July a sharp decrease is seen and the values remain low during the rest of the year. Testosterone plasma levels also exhibit month to month variations. A maximum is found in February and March, and minimal values are measured in August, September, and October. A 5'-monodeiodination activity with a resulting 3,3',5-triiodothyronine (T3) production could be demonstrated in kidney and skin homogenates but not in liver homogenates. Addition of 1,4-dithio-DL-threitol (DTT) and EDTA to the homogenates significantly increases the T3 production. In kidney homogenates incubated with DTT and EDTA a significant annual variation in the T3 production is seen. This T3 production is very high in April, May, and June and is followed by a minimum in July and August. It is concluded that the opposite changes in 5'-monodeiodination activity and plasma T4 concentrations may indicate a peripheral monodeiodination of T4 to T3. During reproduction, which is preceded by a testosterone peak, the increase in the 5'-monodeiodination activity may reflect a greater need for T3.
mesh_terms: D000818:Animals; D004229:Dithiothreitol / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D011895:Rana ridibunda / Q000378:metabolism*; D011898:Ranidae / Q000378:metabolism*; D012621:Seasons; D012867:Skin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology; D014284:Triiodothyronine / Q000096:biosynthesis*
chemical_list: D014284:Triiodothyronine; D013739:Testosterone; D004492:Edetic Acid; D013974:Thyroxine; D004229:Dithiothreitol