J zyxwvutsrqponmlkjihgfedcb Pineal Res zyxwvutsrqponmlk 1993;14:S3-59 Prinred in rhe United Stares of America-ull righrs reserved Copyright zyx 0 Munksgaard. zyx IYY3 zy Journal of Pineal Research ISSN 0742-3098 zyx Thyroxine zyxw 5 ’-deiodinase type I1 activity in chick pineal and Harderian gland: Nyctohemeral rhythmicity and its regulation by - noradrenergic input Rubio A, Menendez-Pelaez A, Reiter RJ. Thyroxine 5’-deiodinase type zyxw I1 activity in chick pineal and Harderian gland: Nyctohemeral rhythmicity and its regulation by noradrenergic input. J. Pineal Res. 1993; 14:53-59. Abstract: Circadian rhythmicity of type I1 thyroxine 5 ’-deiodinase zyxwv (5‘-D) activity was studied in the pineal gland and Harderian glands of chicks. Only Harderian 5’-D activity showed a nyctohemeral rhythmicity with a maximal peak during the day time (1300), while no rhythm of enzyme activity was found in the pineal gland. Besides type I1 5’-D activity, we found high basal levels of the type I isoenzyme in both glands; this activity was specifically suppressed by the addition of 6-n-propyl-thiouracil (PTU). However, day-night differences in Harderian 5’-D activity were maintained even after the addition of PTU. This activity was not affected for either continuous light exposure or darkness during the day. 5‘-D activity seems to be regulated by the noradrenergic input, since the enzymatic activity was stimulated by a P-adrenergic agonist, isoproterenol, and by the a-adrenergic agonist, phenylephrine, in both pineal and Harderian glands. Both drugs affected 5’-D activity in the Harderian gland by stimulating the enzyme activity over basal levels. Introduction Thyroxine 5‘-deiodinase (5’-D, E.C. 3.8.1.4.) is an enzyme which is present in many tissues and is responsible for the conversion of thyroxine (T4) to the most biological active thyroid hormone, tri- iodothyronine or T, [Larsen et al., 19811. Two isoenzymes are known to be involved in this pro- cess, type I and type 11. Type I chiefly maintains the serum levels of the active hormone, while type I1 is present in specific tissues, and seems to play an important role in maintaining intracellular levels of T,, thus being a defense against possible hypothy- roidism. The mechanisms involved in the regulation of the pineal 5’-D type I1 activity have been extensively studied [Reiter et al., 1988; Guerrero et al., 19891. Thus, in rat pineal gland, besides being regulated by the thyroid status, a circadian regulation of enzyme activity by the light-dark cycle has been seen. A A. Rubio, A. Menendez-Pelaez,’ and R.J. Reiter The University of Texas Health Science Center at San Antonio, Department of Cellular and Structural Biology, San Antonio, TX, U.S.A. Key words 5’-0 activrty-chtck-pineal- Harderian gland ’On leave from the Department of Morphology and Cell Biology, University of Oviedo, Oviedo 33006 Spain Address reprint requests to Dr Russel J Reiter, The University of Texas Health Science Center at San Antonio, Department of Cellular and Structural Biology, 7703 Floyd Curl Drive, San Antonio, TX 78284-7762 Received July 8. 1992, accepted October 8, 1992 gradual rise in 5’-D activity after the onset of the dark period occurs with peak values being attained 6 hr later [Tanaka et al., 1986; Guerrero et al., 1988al. This peak is coincident with the rises in N-acetyltransferase (NAT) activity and the melato- nin content of the pineal gland [Guerrero et al., 1988a,b]. The mechanisms responsible for the noc- turnal increase involve the noradrenergic input to the pineal since either light exposure or superior ganglionectorny prevents it [Guerrero et al., 1988a; Murakami et al., 19881. Rhythms in 5’-D type I1 have also been described in the pineal gland of other rodents species, e.g., the Swiss mouse [Rubio et al., 199 1 a], and in other melatonin-producing tissues, e.g., the Harderian gland of the rat [Guer- rero et al., 19871. Circadian rhythms in various enzyme activities have been described in the pineal gland of birds. In the chick pineal gland, clear circadian variations in relation to the melatonin production and in the 53