The type III iodothyronine deiodinase metabolizes the active thyroid hormones thyroxine and 3,5,3'-triiodothyronine to inactive compounds. Recently, we have characterized a Xenopus laevis cDNA (XL-15) that encodes a selenoprotein with type III deiodinase activity (St. Germain, D.L., Schwartzman, R., Croteau, W., Kanamori, A., Wang, Z., Brown, D.D., and Galton, V.A. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 7767-7771). Using the XL-15 as a probe, we screened a rat neonatal skin cDNA library. Among the clones isolated was one (rNS43-1) which contained a 2.1-kilobase pair cDNA insert that manifested significant homology to both the XL-15 and the G21 rat type I deiodinase cDNAs, including the presence of an in-frame TGA codon. Expression studies demonstrated that the rNS43-1 cDNA encodes a protein with 5-, but not 5'-, deiodinase activity that is resistant to inhibition by propylthiouracil and aurothioglucose. Northern analysis demonstrated a pattern of tissue expression in the rat consistent with that of the type III deiodinase and site directed mutagenesis confirmed that the TGA triplet codes for selenocysteine. We conclude that the rNS43-1 cDNA encodes the rat type III deiodinase and that the types I and III deiodinases present in amphibians and mammals constitute a family of conserved selenoproteins important in the metabolism of thyroid hormones.

NG-monomethyl-L-arginine (NMA) and nitroarginine have been reported to be competitive inhibitors of the production of endothelium-derived relaxing factor (EDRF). In chronically instrumented conscious rats, we observed that the pressor response of NMA was attenuated by pretreatment with L-arginine but not by pretreatment with D-arginine, phentolamine, or meclofenamate. Inhibitors of the renin-angiotensin system, captopril and [Sar1,Ile5,Thr8]angiotensin II, did not significantly affect the pressor response of NMA, either. Ten to fifteen minutes after bolus administration of 7-15 mg/kg NMA, when baseline blood pressure was virtually restored, the pressor responses of angiotensin II (ANG II), norepinephrine, and arginine vasopressin were significantly potentiated by approximately 30-40% compared with control values. This potentiation was prevented by pretreatment with L- but not D-arginine. It was also observed in conscious rats subjected to ganglionic blockade. Likewise, the pressor responses of ANG II were significantly increased during infusions of 2 and 5 micrograms/min nitroarginine methyl ester (NAME), dosages that raised baseline blood pressure by 6 +/- 2 and 15 +/- 3 mmHg, respectively. During administration of 5 and 50 micrograms/min NAME, hypotensive responses of methacholine and histamine were only modestly attenuated compared with the responses recorded during infusions of phenylephrine, which raised resting blood pressure to comparable levels. Finally, in freshly isolated rat aorta, NMA inhibited basal and stimulated production of guanosine 3',5'-cyclic monophosphate in a manner comparable to reduced hemoglobin, a known inhibitor of EDRF.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytogenetic studies were made on Japanese raccoon dogs (Nyctereutes procyonoides viverrinus) that were caught in the wild in southern Kyushu and northern Honshu. G-banding, C-banding, acridine orange (AO) staining following BudR incorporation, and silver staining for nucleolar organizer regions (NORs) were performed on chromosomes from fibroblast cultures. Modal numbers varied from 40 to 42. The karyotype comprised 26 mediocentric and 10 acrocentric autosomes, a submetacentric X, and a minute submetacentric Y. Unpaired B chromosomes which differed in number between animals accounted for the variable modal numbers. B chromosomes stained indistinctly with G-banding but showed a variety of positive patterns with C-banding and differentiated staining with AO. NORs were observed on the telomeric ends of the long arms of chromosomes 11, 12, and 18. No cytogenetic differences were seen between the northern and southern animals.

During recent studies of receptor binding of T3 and T4 in tadpole red blood cells (RBCs), it was found that the fractional uptake of T3 was 3-5 times greater than that of T4. The present studies were performed to determine if this difference was due to facilitated uptake of T3. All studies were performed in cells incubated at 22 C in phosphate-buffered amphibian or mammalian Ringer solution containing 10(-11) M [125I]T3 or [125I]T4, with or without nonradioactive L-T3, D-T3, or L-T4 in concentrations ranging from 10(-10) to 2 X 10(-7) M. In tadpole, frog, rat, and human RBCs and in rat thymus cells, the rate of uptake of [125I]T3 and its appearance in the cytosol (extranuclear) fraction of the cell was greatly retarded in the presence of 10(-7) M T3. This effect was not due to saturation of the T3-binding proteins in cytosol, since the presence of 10(-7) M T3 did not influence the percentage of [125I]T3 in cytosol at equilibrium. These data suggest the presence of a saturable system for the cellular uptake of T3. T4 (10(-7) M) had relatively little effect, and D-T3 (10(-7) M) had no effect on this system. No saturable system for T4 uptake could be demonstrated, and at low concentrations of hormone, T4 uptake was only 10-30% of T3 uptake, although the binding activities of cytosol and cellular uptake via nonsaturable systems were quantitatively similar for both hormones. From kinetic studies of [125I]T3 uptake, it was found that at low concentrations of T3 (10(-11)-10(-9) M), the saturable system accounted for more than 60% of the total uptake of [125I]T3. The apparent Km values of the saturable system in RBCs of tadpole, frog, and rat were 4.5 +/- 0.09 (+/- SE), 5.7 +/- 1.10, and 4.6 +/- 0.73 X 10(-8) M T3, respectively. Corresponding values for maximum velocity were 5.92 +/- 1.02, 2.86 +/- 0.70, and 2.08 +/- 0.34 pmol/min X 10(7) cells. In rat thymus cells, the Km was 16.9 +/- 0.93 X 10(-8) M, and the maximum velocity was 9.10 +/- 0.5 pmol/min X 10(7) cells. The saturable uptake system was not influenced by ouabain, dinitrophenol, sodium fluoride, oligomycin, or sodium cyanide. These findings suggest that the uptake of T3, but not T4, into some tissues is facilitated by a specific carrier-mediated system that is not dependent on metabolic energy.(ABSTRACT TRUNCATED AT 400 WORDS)

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