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Peroxidase and NADPH-Cytochrome C Reductase Activity During Thyroid Hyperplasia and Involution

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Peroxidase and NADPH-Cytochrome C Reductase Activity During Thyroid Hyperplasia and Involution Peroxidase and NADPH-Cytochrome C Reductase Activity During Thyroid Hyperplasia and Involution KUNIHIRO YAMAMOTO AND LESLIE J. DEGROOT Thyroid Study Unit, Department of Medicine, University of Chicago, Chicago, Illinois 60637 ABSTRACT. The regulation of iodination was in- TSH injection, whether expressed per mg gland vestigated in male rats during physiological altera- weight, per mg protein, or per fxg DNA, suggesting tions in thyroid function. Thyroid hyperplasia was enzyme induction and cellular hypertrophy. Involu- Downloaded from https://academic.oup.com/endo/article/95/2/606/2618917 by guest on 30 September 2021 produced by giving 0.01% PTU in drinking water or tion by T4 administration caused a decrease in injection of TSH (2 USP U/day); involution was thyroid weight, DNA content, and enzyme activity per induced after PTU treatment by giving 3 fig L-T4/ml gland. The main reason for the decrease in enzyme in drinking water. Increase in activity of thyroid activity per gland was a diminution of cell numbers. peroxidase and NADPH-cytochrome c reductase per During thyroid hyperplasia and involution, perox- gland exceeded gains in thyroid weight and DNA idase and NADPH-cytochrome c reductase activity content early in hyperplasia, but increased essen- is regulated by TSH. During the onset of TSH tially in parallel manner during chronic PTU treat- action, peroxidase and NADPH-cytochrome c re- ment. Enzyme activity per /xg DNA increased to ductase increase to a greater extent than thyroid 155% of control after 4 days of PTU treatment, weight and DNA content, suggesting preferential decreased to 138% on the seventh day, and was at enzyme synthesis in addition to cell hypertrophy. the control level after 21 days of treatment. Cellular (Endocrinology 95: 606, 1974) enzyme activity also increased after seven days of HE activity of thyroid peroxidase adjusted to 7.4 with sodium phosphate buffer. T is augmented by chronic TSH treat- Other groups of rats were given 1 USP U TSH ment and is depressed by thyroxine treat- in 0.5 ml of saline by injection subcutaneously ment (1,2). TSH is also known to cause twice a day for 1 to 7 days. (The TSH was a gift hyperplasia of the thyroid (3). It is of of the National Institutes of Health.) For induc- tion of thyroid involution, L-thyroxine (Sigma interest to study the change in the ac- Chemical Co.) 3 /ug/ml was added to drinking tivities of the enzymes involved in thyroid water containing 0.01% PTU on the 21st hormone synthesis to determine whether through the 30th days from the beginning of TSH can specifically induce these en- PTU treatment. The rats were anesthesized zymes. For this purpose, the activities of lightly with ether and sacrified by exsanguina- peroxidase and NADPH-cytochrome c re- tion. The thyroids from each group were ex- ductase, thyroid weight and DNA content cised, chilled, trimmed of connective tissue, have been determined during the de- weighed, and pooled. Each group of thyroids velopment of thyroid hyperplasia and in- was homogenized in modified Krebs-Ringer- 5 volution. phosphate buffer containing 10~ M KI and cen- trifuged at 105,000 x g for 1 hr. The pellets were washed once and resuspended in the same Materials and Methods buffer. Peroxidase activity was estimated by Male Charles River CD rats were fed Purina thyrosine iodinase assay. The assay system Chow. At the beginning of the experiment the contained participate protein (80-120 fxg), 0.5 average body weight was 100 g (85-120 g). To ml K-R-phosphate buffer at pH 7.0, 10 nmoles 131 induce thyroid hyperplasia, 0.01% propyl- KI, 1 fxCi I, 1 /Ltmole glucose, 0.1 mg glucose thiouracil (PTU) was added to the drinking oxidase (Type II, Sigma Chemical Co.) and 1 water for periods ranging from 1 to 41 days. The /Ltmole tyrosine (Sigma Chemical Co.), in 1 ml. pH of the drinking water containing PTU was Incubation was started by adding glucose ox- idase and stopped with 2 drops of 2N HC1 after 20 min at 37 C. The percentage of iodide Received September 4, 1973. Supported by United States Public Health Service formed into iodotyrosine was assessed by count- Grant No. AM-13,377. ing radioactivity adsorbed by cation exchange 606 IODINATION AND THYROID HYPERPLASIA 607 resin (Fisher Scientific Co.) at pH 2.0 (4). NADPH-cytochrome c reductase assay system 5 consisted of participate protein (80-120 /xg), 0.4 o ml of 0.2M sodium phosphate buffer at pH 7.0, 1 O_ oOC /xmole KCN, 50 nmoles cytochrome c (type III o horse heart, Sigma Chemical Co.) and 100 nmoles NADPH (Sigma Chemical Co.), in 1 ml. KCN was added to inhibit any effects of mitochondrial enzymes on reduction of cyto- Downloaded from https://academic.oup.com/endo/article/95/2/606/2618917 by guest on 30 September 2021 chrome c. The reaction, at room temperature, was started by adding NADPH and recorded by spectrophotometry at 550 m/i. DNA was deter- mined in duplicate by a modified Schmidt- Thannhausser-Schneider method (5). One-tenth ml of 20% homogenate (w/v) from 100 mg 0.010-1 thyroid was made up to 1 ml in ice water, and (B) NADPH-cytochrome cy then precipitated and washed twice with 0.5 ml reductase of 0.6N perchloric acid (PCA). The pellet was incubated with 0.8 ml of 0.3N KOH for one hour at 37 C. The acid-insoluble precipitate obtained c E after alkaline hydrolysis was washed with 1.2N O" 0.005- PCA. After the pellet was extracted with 0) ethanol-ether (3:1, V:V), it was hydrolyized with =1 0.8 ml of 0.5N PCA for 15 min at 90 C to release free bases. DNA content was estimated by spectrophotometry at 265 m/u,. The unknown sample was compared to a standard curve 10 100 200 derived from aliquots of commercial purified fxq PROTEIN DNA (Sigma Chemical Co.) carried through the same procedure. Protein was determined in FIG. 1. Enzyme activities of peroxidase and NADPH- duplicate by the method of Lowry et al. (6). cytochrome c reductase as a function of enzyme protein concentration. Particulate fractions from non- stimulated thyroid (—•—) and hyperplastic thyroid Results after 41 days of PTU treatment ( A ) were used. It was necessary to pool thyroid tissue The assays were done as indicated in Materials and from groups of seven control animals in Methods. order to have sufficient material for each enzyme and DNA assay. Since the hyper- Change in thyroid weight and DNA con- plastic thyroids became about 5 times larger tent during treatment programs than those of the control group, dose re- Two days after introduction of PTU in sponse curves for both peroxidase and drinking water, thyroid weight increased NADPH-cytochrome c reductase assay significantly, doubling on the fourth day were made using particulate fraction from (Fig. 2, A). The increase in thyroid weight normal and hyperplastic thyroid in order to and DNA content per gland was linear validate the assay system (Fig. 1, A and B). until the 11th day. Thereafter, the rate of Both enzyme activities showed linearity of change decreased, although hyperplasia response over a range of 10-200 fig of still continued after 41 days of PTU treat- particulate fraction protein. Assays were ment. subsequently performed with nearly the TSH was injected subcutaneously (2 same amount of particulate protein (80-120 USP U/day) for 1 to 7 days. After 7 days, /ug/tube) from the control or treated there was a significant increase in thyroid thyroids in each test. weight (Fig. 3, A). "Involution" was 608 YAMAMOTO AND DEGROOT Enclo • 1971 Vol 95 • No 2 80- 300 FIG. 2. Changes of thyroid weight, DNA content, and ac- tivity of peroxidase and 50- h200 NADPH-cytochrome c reduc- Q tase during PTU treatment. A. o> Thyroid weight and DNA con- •100 tent. Thyroid weights (— • —) Downloaded from https://academic.oup.com/endo/article/95/2/606/2618917 by guest on 30 September 2021 are presented as a mean ± SD from 7 animals and DNA ( o ) is presented as an average of two samples. B. Per- centage change of peroxidase Q 6 < B and NADPH-cytochrome c re- ^_^ -*• o 400- ductase activity per gland and * Peroxidase DNA content per gland. En- Ul 0. o NADPH-cytochrome c reductose zyme activities are averages of f / A DNA 300- /1 / three samples and DNA is av- erage of two samples. — • — J peroxidase per gland, —o — o 200- / o NADPH-cytochrome c reduc- tase per gland, A DNA dl 100- & per gland. C. Percentage i change of specific activity. Specific activity of enzyme was 2001 estimated as activity per /ng • Peroxidase DNA. pecific activity per mg o o NADPH-cytochrome c reductase protei;. and per mg thyroid weight was almost the same as O per /xg DNA. — • — Perox- o 100 idase, — o— NADPH- cytochrome c reductase. 12 4 7 11 21 31 DAYS achieved by T4-treatment of rats with idase and NADPH-cytochrome c reductase PTU-induced hyperplastic glands. The de- were parallel during all treatment pro- crease in thyroid weight was significant on grams. When rats were treated with PTU, the second day and was 50% on the 9th day the rate of increase of both enzyme ac- as compared with the group which re- tivities decreased after the 7th day of ceived PTU treatment alone for the same treatment. Between the 2nd day and the period (Fig. 4, A). DNA content per gland 11th day of PTU treatment, enzyme ac- also decreased, but after 6 days DNA tivities increased to a greater extent than content per weight of thyroid was higher DNA content (Fig.
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