Tanshinone IIA inhibits human prostate cancer cells growth by induction of endoplasmic reticulum stress in vitro and in vivo.

BACKGROUND: Tanshinone IIA (Tan-IIA) is one of the major lipophilic components isolated from the root of Salviae Miltiorrhizae Radix. We explored the mechanisms of cell death induced by Tan-IIA treatment in prostate cancer cells in vitro and in vivo. METHODS: Cells were treated with Tan-IIA and growth inhibition was assessed. Cell cycle profiles after Tan-IIA treatment were determined by flow cytometry. Expression levels of cell cycle regulatory proteins and apoptosis-related proteins were determined after Tan-IIA treatment. Expression levels of endoplasmic reticulum (ER) stress-regulated genes were determined to investigate their role in Tan-IIA-induced cell death. GADD153 expression was knocked down by small interfering RNA (siRNA) transfection. Rate of cell death and proliferation was obtained by 3-(4,5-dimethyl thizol-2-yl)-2,5-diphenyl tetrazolium bromide assay. Antitumor activity of Tan-IIA was performed in LNCaP xenograft model. RESULTS: Our results showed that Tan-IIA caused prostate cancer cell death in a dose-dependent manner, and cell cycle arrest at G0/G1 phase was noted, in LNCaP cells. The G0/G1 phase arrest correlated with increase levels of CDK inhibitors (p16, p21 and p27) and decrease of the checkpoint proteins. Tan-IIA also induced ER stress in prostate cancer cells: activation and nuclear translocation of GADD153/CCAAT/enhancer-binding protein-homologous protein (CHOP) were identified, and increased expression of the downstream molecules GRP78/BiP, inositol-requiring protein-1α and GADD153/CHOP were evidenced. Blockage of GADD153/CHOP expression by siRNA reduced Tan-IIA-induced cell death in LNCaP cells. Tan-IIA also suppressed LNCaP xenograft tumor growth, causing 86.4% reduction in tumor volume after 13 days of treatment. CONCLUSIONS: Our findings suggest that Tan-IIA causes G0/G1 cell cycle arrest in LNCaP cells and its cytotoxicity is mediated at least partly by ER stress induction. These data provide evidence supporting Tan-IIA as a potential anticancer agent by inducing ER stress in prostate cancer.

Molecular epidemiology and antigenic analyses of influenza A viruses H3N2 in Taiwan.

The severity of an influenza epidemic season may be influenced not only by variability in the surface glycoproteins, but also by differences in the internal proteins of circulating influenza viruses. To better understand viral antigenic evolution, all eight gene segments from 44 human H3N2 epidemic strains isolated during 2004-2008 in Taiwan were analyzed to provide a profile of protein variability. Comparison of the evolutionary profiles of the HA, NA and PB2 genes of influenza A (H3N2) viruses indicated that they were derived from a group of H3N2 isolates first seen in 2004. However, the PA, M and PB1 genes were derived from a different group of H3N2 isolates from 2004. Tree topology revealed the NP and NS genes could each be segregated into two groups similar to those for the polymerase genes. In addition, new genetic variants occurred during the non-epidemic period and become the dominant strain after one or two seasons. Comparison of evolutionary patterns in consecutive years is necessary to correlate viral genetic changes with antigenic changes as multiple lineages co-circulate.

Differences in the nearpoint of convergence with target type.

PURPOSE: The purpose of this study was to determine the effect on measurements of the nearpoint of convergence (NPC) of different target types. In order to assess the influence of accommodation, the NPC was also measured under conditions of varying accommodative demand. METHODS: The NPC was measured to the nearest 0.5 cm using three targets: the RAF rule, the sharpened tip of a pencil and the tip of the examiner's index finger. All measurements were performed under the same conditions on two groups of asymptomatic subjects, a group of 14 presbyopic subjects and a group of 14, younger, non-presbyopic subjects. The influence of accommodative demand was assessed in the non-presbyopic group by measuring the NPC while subjects viewed the RAF rule target through +2.00 and -2.00 lenses held in front of their eyes. RESULTS: For the presbyopic group, the NPC (break) and NPC (recovery) were independent of target type. However, the NPC (break) was significantly less remote than the NPC (recovery). Comparative data for the non-presbyopic group showed that NPC (break) for the RAF target was less remote than for either the pencil tip or finger tip targets. In agreement with the results from the presbyopic group, the NPC (recovery) was independent of target type. CONCLUSION: For subjects with little or no accommodation, the NPC does not depend on the target used and is the same measured with the RAF rule, a pencil tip or finger tip. In non-presbyopic subjects there appears to be a small accommodative influence on the NPC, which is target dependent. However, the difference is probably not clinically important.

Barriers to providing diabetes care in community health centers.

OBJECTIVE: We aimed to identify barriers to improving care for individuals with diabetes in community health centers. These findings are important because many such patients, as in most other practice settings, receive care that does not meet evidence-based standards. RESEARCH DESIGN AND METHODS: In 42 Midwestern health centers, we surveyed 389 health providers and administrators about the barriers they faced delivering diabetes care. We report on home blood glucose monitoring, HbA1c tests, dilated eye examinations, foot examinations, diet, and exercise, all of which are a subset of the larger clinical practice recommendations of the American Diabetes Association (ADA). RESULTS: Among the 279 (72%) respondents, providers perceived that patients were significantly less likely than providers to believe that key processes of care were important (overall mean on 30-point scale: providers 26.8, patients 18.2, P = 0.0001). Providers were more confident in their ability to instruct patients on diet and exercise than on their ability to help them make changes in these areas. Ratings of the importance of access to care and finances as barriers varied widely; however, >25% of the providers and administrators agreed that significant barriers included affordability of home blood glucose monitoring, HbA1c testing, dilated eye examination, and special diets; nonproximity of ophthalmologist; forgetting to order eye examinations and to examine patients' feet; time required to teach home blood glucose monitoring; and language or cultural barriers. CONCLUSIONS: Providers in health centers indicate a need to enhance behavioral change in diabetic patients. In addition, better health care delivery systems and reforms that improve the affordability, accessibility, and efficiency of care are also likely to help health centers meet ADA standards of care.

Mandibular second molar periodontal status after third molar extraction.

BACKGROUND: Extraction and treatment of third molars have been cited as causing periodontal problems. To evaluate the long-term effects of third molar extraction on the periodontal health of the mandibular second molar, a comparison of the periodontal status was performed around 2 groups of mandibular second molars, with and without third molar extraction. METHODS: A total of 312 sites in 57 adult periodontitis patients were examined and the buccal and lingual locations of the mesial and distal root surfaces around the second molars were recorded. Two-hundred and thirty-two sites were experimental teeth; i.e., third molars had been surgically removed more than 5 years ago, 80 sites served as control molars; i.e., congenitally missing third molars. Clinical periodontal parameters including probing depth, attachment loss, and gingival recession and radiographic intrabony level were measured. The effects of the surgery and the examination (buccal or lingual) locations on the measurements were statistically analyzed. RESULTS: Neither extraction history nor examination location affected the probing depth on mesial surfaces. However, significant effects of the surgical history on the probing depth were observed on the distal surfaces. Similar results of greater attachment loss and radiographic alveolar bone loss were observed only at the distal sites of the experimental group. In addition, the increased radiographic bone loss was only found at the distal sites (adjacent to the surgical location) and not at the mesial sites (distant from the surgical location) on the experimental group. CONCLUSIONS: In this study, greater periodontal breakdown, including probing depth, attachment loss, and radiographic alveolar bone loss, was found at the distal sites, but not at the mesial sites, of the experimental molars where the third molar was surgically extracted compared with the control teeth (no surgery). In the experimental molars, more radiographic bone loss was found at the sites adjacent to the surgical location than at the sites distant to the surgical location. Therefore, we suggest that the surgical removal of the mandibular third molar may lead to a periodontal breakdown on the distal surface of the second molar. Periodontal re-evaluation after the initial healing of third molar extraction is indicated.

Ameliorated effect of L-arginine supplementation on gingival morphology in cyclosporin-treated rats.

BACKGROUND: The role of nitric oxide (NO) in the pathogenesis of cyclosporin (CsA)-induced gingival overgrowth is unknown. The purpose of the present study was to evaluate the effect of NO substrate (L-arginine) and blockade (N-nitro-L-arginine methylester-hydrochloride, L-NAME) on the gingival morphology in CsA-fed rats. METHODS: Sixty CsA-fed (10 mg/kg/day) male Sprague-Dawley rats were assigned to 3 groups. Animals in 2 experimental groups received L-arginine (1% weight/weight) in rat chowder or L-NAME (50 mg/l) in drinking water, respectively, for 4 weeks. Rats in the control group were fed a normal diet and water. At week 0, 2, and 4, dental stone models were made from the mandibular anterior region and the gingival dimensions (width, depth, and height) were measured. The tail cuff blood pressure and the plasma nitrate level were also measured at week 4 to monitor the effects of L-arginine and L-NAME treatment. RESULTS: No significant difference in the gingival dimensions was noticed at week 0; however, significant differences were observed at weeks 2 and 4, except the buccolingual depth at week 2. While the magnitude of gingival dimensions was large, moderate, and small in control, L-NAME, and L-arginine groups, respectively, we found significantly reduced gingival dimensions in both L-arginine supplement and L-NAME groups. Nevertheless, the reduced gingival overgrowth in the L-NAME treatment group was far less than that in the exogenous NO treatment group. Plasma NO2-/NO3- concentrations were also significantly different; i.e., from the highest to the lowest levels were the L-arginine, CsA control, and L-NAME group, respectively. A significantly increased mean and diastolic blood pressure was found in the L-NAME group compared to the L-arginine group. CONCLUSIONS: Gingival morphology in CsA-fed rats was evaluated after NO substrate (L-arginine) and blockade (L-NAME) treatment for 4 weeks. Significantly decreased dimensions were noted in the L-arginine group compared to the CsA group at weeks 2 and 4. Although an inhibitory effect on the gingival morphology was also observed in the L-NAME group, another unknown mechanism might be involved. Within the limitations of the study, we suggest that NO may have an important role in the mechanism of CsA-induced gingival overgrowth.

Telomerase activity correlates with cell cycle regulators in human hepatocellular carcinoma.

AIMS/BACKGROUND: Mutation in cell cycle genes is the most common genetic change in malignant tumor cells. Telomerase activation, considered as essential in the immortality of cancer cells, is found in most cancers, where there may be an association with an active cell cycle. METHODS: In this study study we used the TRAP assay to determine telomerase activity in liver tumor specimens from 25 cases of hepatocellular carcinoma (HCCs) as well as in corresponding non-cancerous liver tissue in each patient. The expression of cyclin D1, cdk2, and cdk4 protein was also examined by Western blot. RESULTS: Twenty-one of the 25 cases of HCC were found to have increased telomerase activity, whereas only five out of the 25 non-cancerous liver samples were found to have weak telomerase activity. Telomerase activity was not found to be related to tumor size, HBsAg, HBeAg, anti-HCV, transaminase, or alpha-fetoprotein serum titer. Furthermore, three out of the 25 cases of HCC showed cyclin D1 overexpression, whereas 15 of the 23 cases of HCC showed decreased cyclin D1 expression. Down regulation of cyclin D1, cdk2, cdk4 protein correlated with telomerase activity (p<0.004, p<0.013, and p<0.001 respectively). CONCLUSION: The results indicate that genetic defects in HCC facilitate the reactivation of telomerase activity, a process which may be dependent on cyclin D1 with its cyclin dependent kinase (cdk) partner defect.

Quality of diabetes care in community health centers.

OBJECTIVES: This study assessed the quality of diabetes care in community health centers. METHODS: In 55 midwestern community health centers, we reviewed the charts of 2865 diabetic adults for American Diabetes Association measures of quality. RESULTS: On average, 70% of the patients in each community health center had measurements of glycosylated hemoglobin, 26% had dilated eye examinations, 66% had diet intervention, and 51% received foot care. The average glycosylated hemoglobin value per community health center was 8.6%. Practice guidelines were independently associated with higher quality of care. CONCLUSIONS: Rates of adherence to process measures of quality were relatively low among community health centers, compared with the targets established by the American Diabetes Association.

Molecular studies into the role of CD44 variants in metastasis in gastric cancer.

CD44, an integral membrane glycoprotein expressed by many cell types, serves as the principal transmembrane hyaluronate receptor and might be a determinant of metastatic and invasive behaviour in carcinomas. The generation of CD44 splice variants might be linked closely with gastric carcinoma tumorigenesis and differentiation. Some studies have reported that the magnitude of CD44 variant synthesis at the protein level correlates with lymph node metastasis. A number of studies have examined the possible mechanism of involvement of the CD44 variant in tumour metastasis. Most studies have reported that the regulation of CD44 binding to hyaluronate results from glycosylation of variably spliced exons. Direct hyaluronate binding studies of CD44 V4-V7 isoforms transfected into the human gastric carcinoma cell line, SC-M1, have indicated that the V4-V7 isoforms themselves, in addition to glycosylation, can alter hyaluronate binding.

[Molecular typing of Taiwanese Orientia tsutsugamushi isolates by restriction fragment profile].

Scrub typhus, which is caused by Orientia tsutsugamushi, is one of the reportable diseases in Taiwan, ROC. Positive cases seemed to be increasing in recent years and our laboratory had confirmed a total of 247 cases in 1997. In this study, 71 strains of O. tsutsugamushi were isolated from heparinized blood of the patients by cell culture, and their DNA was isolated. Two-step polymerase chain reaction was then used to amplify a specific sequence from the DNA, which was digested with restriction enzymes, Hha I and Sfa NI, for typing. With this technique, 34 strains gave rise to the same profile as that of the Kuroki type, 6 as the Karp type and 2 as the Gilliam type. The remaining 28 strains produced fragment profiles different from those of types Karp, Kato, Kawasaki, Kuroki, Gilliam and Shimokoshi and, therefore, were classified as 6 new types designated Taiwan A to Taiwan F, respectively. These strains with profiles different from those of the standard Japanese strains may represent the local mutant strains.

Mutation analysis of pertussis toxin promoter.

The improving of the expression efficiency of a pertussis toxin (PT) promoter was believed to be a critical issue for the production of PT in acellular vaccine development. In this study, we have isolated a PT promoter region from the genome of a pertussis strain ATCC 9340. Based on the promoter sequence, a series of mutant PT promoters have been generated and subjected to in vitro gel shift analysis and in vivo reporter beta-galactosidase activity study. As compared with the wild type promoter, the mutation of the ribosome binding sequence or -10 element, to the respective consensus sequence derived from strong bacterial promoters, resulted in an enhancement of its interaction with two cellular proteins, and a slightly higher beta-galactosidase activity (1.3 fold). Whereas, the change of either upstream inverse repeats or 20-bp direct repeats to a certain complete repeat significantly promoted the formation of another DNA-protein-complex, and exhibited an 1.8 fold beta-galactosidase activity. These findings would have provided a mutation target for making a more efficient PT-production pertussis strain.

The extent of proliferative and apoptotic activity in intraductal and invasive ductal breast carcinomas detected by Ki-67 labeling and terminal deoxynucleotidyl transferase-mediated digoxigenin-11-dUTP nick end labeling.

BACKGROUND: The balance among cell proliferation, cell differentiation, and cell death determines the cell number in a population as well as the size or even the stage of a tumor. Thus, to improve our understanding of the pathogenesis of neoplasms, it is important to investigate the regulation of both cell proliferation and cell death. METHODS: This study examined the occurrence of apoptosis and proliferative capacity in 46 breast carcinomas: 20 intraductal carcinomas (ductal carcinomas in situ [DCIS]) and 26 infiltrative ductal carcinomas (IDC). Terminal deoxynucleotidyl transferase-mediated digoxigenin-11-dUTP nick end labeling (TUNEL) and immunostaining with the Ki-67 antibody were used in the examination. A ladder of DNA fragments induced by apoptosis was demonstrated by means of DNA agarose gel electrophoresis in 10 of the available TUNEL positive and negative samples. RESULTS: The results were correlated with p53, bcl-2, estrogen receptor (ER), and progesterone receptor (PR) protein expression, which would suggest association with apoptosis by immunohistochemistry. The apoptosis and proliferation of each cancer were expressed as the number of tumor cells undergoing apoptosis and proliferation per 1000 tumor cells. The extent of apoptosis was more frequently observed in DCIS than in IDC (21.9+/-6.8 vs. 4.0+/-0.9, P < 0.001), and the proliferation activity was significantly higher in IDC than in DCIS (16.8+/-6.5 vs. 3.5+/-0.8, P < 0.006). Apoptosis associated with MIB-1 positive cells and TUNEL labeling was significantly higher in IDC than in DCIS (3.26 vs. 0.42, P=0.001). In DCIS, apoptosis was correlated with p53 (r=0.663, P=0.005), and p53 had a reverse correlation with bcl-2 (r=0.620, P= 0.018). Moreover, bcl-2 expression was associated with ER (P=0.028) and PR (P= 0.005) expression in both DCIS and IDC. CONCLUSIONS: The results of this study show that a higher degree of apoptosis and lower proliferation activity in intraductal carcinoma result in a steady-state, self-renewing condition in which net growth of the tumor is rare. The results also indicate that apoptosis was altered by the expression of p53, bcl-2, ER, and PR.

Apoptosis occurs more frequently in intraductal carcinoma than in infiltrating duct carcinoma of human breast cancer and correlates with altered p53 expression: detected by terminal-deoxynucleotidyl-transferase-mediated dUTP-FITC nick end labelling (TUNEL).

AIMS: We examined the relationship between apoptosis and three different major stages of human breast carcinoma: intraductal carcinoma (DCIS), infiltrating duct carcinoma (IDC) and metastatic carcinoma in lymph nodes. We also determined the correlation between apoptosis and oestrogen receptor (ER), progesterone receptor (PR) and p53. METHODS AND RESULTS: The study investigates the extent of apoptosis in 63 breast carcinomas by in-situ end-labelling, in formalin-fixed, paraffin-processed tissue sections. The 63 breast carcinomas, included 22 DCISs, 26 IDCs, three infiltrating lobular carcinomas (ILC) and 12 metastatic lymph nodes. The apoptotic labelling index was higher in DCIS than IDC and metastatic carcinoma (P < 0.001, P < 0.007, respectively). By immunohistochemistry, we also analysed p53, ER and PR. Apoptosis correlated significantly with p53 (r = 0.748, P = 0.0004) in IDC. Also, ER correlated significantly with PR (r = 0.629, P = 0.00001). No apparent correlation was found between the apoptosis and ER or PR. CONCLUSION: Our data suggest that not only does apoptosis differ between intraductal carcinoma and infiltrating carcinoma but also it might be regulated by altered p53 expression.

Losartan reduces ethanol intoxication in the rat.

Results of a previous study showed that ethanol inhibition of hippocampal long-term potentiation (LTP) induction was mediated by angiotensin II (AII) and the AT1 subtype receptor because it was blocked by losartan, a specific AT1 antagonist. Because LTP is an important hippocampal function involved in the memory process and other behaviors, it is possible that losartan might block some of the directly observable ethanol-induced changes in rat behavior. Results demonstrate that losartan can effectively block some of the intoxicating effects of low doses of ethanol, 2 g/kg PO or IP. However, even a high dose of losartan 20 mg/kg IP, did not reduce significantly any of the intoxicating effects of the higher dose of 4 g/kg administered by gavage. Higher doses of ethanol might be more difficult to block because of a direct effect on the post synaptic membrane.

Peroxidatic degradation and ether link cleavage of thyroxine in a particulate fraction of human thyroid.

The present study was undertaken to investigate degradation of thyroxine (T4) mediated by thyroid peroxidase in man. A particulate fraction (1,000-100,000 x g) of normal human thyroid tissue was prepared and used as crude enzyme. 125I-T4 and unlabeled T4 were incubated with the particulate fraction in buffer containing glucose and glucose oxidase for generation of H2O2. After incubation, iodoamino acids were extracted with ethanol and the products of T4 degradation were analyzed by thin layer chromatography. In this system, T4 was degraded in time-, temperature- and pH-dependent manners, but not in the absence of the H2O2-generating system. The rate of degradation was related to concentration of the particulate fraction. The reaction was inhibited by methimazole, propylthiouracil and catalase. When [3',5'-125I] T4 was used as a tracer, major labeled products of T4 degradation were inorganic iodide and ethanol-unextracted fraction and no detectable labeled 3,5,3'-triiodothyronine (T3) or 3,3',5'-triiodothyronine (rT3) was generated. From a kinetic study by adding various doses of unlabeled T4, the apparent Km value for T4 was 30 microM and the Vmax value was 230 pmol/mg protein/min. When [3,5-125I] T4 was incubated with enzyme preparation, one third of degraded T4 was recovered as diiodotyrosine (DIT) and half of 125I-DIT was degraded in parallel incubation. No formation of radiolabeled DIT was observed in incubation with Na- 125I done in tandem. These findings suggest that thyroid hormones can be metabolized by peroxidase in human thyroid by pathways that include cleavage of ether linkage.

Effects of in vivo triiodothyronine and long acting thyroid stimulator (LATS) administration on the vitro thyroid cAMP response to thyrotrophin and LATS.

The present study was undertaken to examine the effects of prolonged in vivo treatment with T3 and long acting thyroid stimulator (LATS) on in vitro responsiveness of mouse thyroid cyclic AMP to thyrotrophin (TSH) and LATS-immunoglobulin G (IgG). In control mice, thyroid cAMP concentrations after incubation with normal-IgG (10 mg/ml) for 2 h, TSH (10 mU/ml) for 10 min and LATS-IgG (10 mg/ml) for 2 h were 1.25 +/- 0.11 (mean +/- SE) (n = 5), 15.87 +/- 3.47 (n = 6) and 2.17 +/- 0.25 pmoles/mg wet weight (n = 6), respectively. In mice given T3 (5 micrograms/ml) in drinking water for 5 days, thyroid cAMP concentrations after an incubation with TSH were reduced by 50%, as compared to those of the control mice. They were also decreased in mice injected ip with 5 mg of LATS-IgG (1000%/5 mg in the McKenzie bioassay) daily for 5 days. Combined treatment with T3 and LATS decreased the cAMP response to TSH only to the same extent as did T3 alone, indicating that the inhibitory effects of T3 and LATS were not additive. Similar findings were observed with the thyroid cAMP response to LATS-IgG in vitro; either T3 or LATS treatment in vivo decreased cAMP response to LATS-IgG in vitro, but combined treatment with T3 and LATS did not cause further inhibition as compared with T3 or LATS treatment alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid hormone secretion is more sensitive than thyroid cyclic AMP accumulation to stimulation with LATS in mice in vitro and in vivo.

The effects of LATS-immunoglobulin G (IgG) on thyroid hormone secretion and on thyroid cAMP concentrations were investigated in mice and compared to those of TSH. In the in vitro experiments, thyroid lobes were incubated in Krebs-Ringer bicarbonate buffer with LATS-IgG or TSH for 3 h or 2 h and T3 concentrations in buffer and thyroid cAMP were measured by RIA. T3 in the buffer was increased with 1.5 mg/ml of LATS-IgG (A) or 2.5 mg/ml of LATS-IgG (B) (1000%/5 mg or 400%/5 mg in the McKenzie bioassay, respectively), whereas thyroid cAMP was elevated only after incubation with two to four times higher doses of LATS-IgG (A) or LATS-IgG (B). 0.03 mU/ml of TSH increased T3 concentrations, while a two fold higher dose of TSH was required to increase thyroid cAMP. In the in vivo study, 5 mg of LATS-IgG (A) injected intravenously increased serum T4 concentrations but not thyroid cAMP. 2 mU of TSH increased serum T4, while 10 mU was needed to elevate thyroid cAMP. These results indicate that: i) thyroid hormone secretion is more sensitive than increases of thyroid cAMP to stimulation with LATS, which is similar to stimulation with TSH and that: ii) thyroid hormone secretion rather than increases of thyroid cAMP should be employed to detect serum thyroid stimulating activities when mouse thyroids are used.

Effects of intrathyroidal metabolism of thyroxine on thyroid hormone secretion: increased degradation of thyroxine in mouse thyroids stimulated chronically with thyrotrophin.

Mice were infused continuously with graded doses of bovine TSH (bTSH) and changes in plasma concentrations of bTSH and T4 were measured. Then mice infused with 100 mU TSH per day were sacrificed on days 0, 1, 3 and 5 and their thyroids were excised to determine in vitro secretion of T4, T3 and rT3 during 3 h of incubation. At the end of the incubation, thyroidal contents of T4, T3 and rT3 were also determined after pronase digestion. Plasma bTSH levels were increased on day 1 to a level of 110 microU/ml and remained unchanged thereafter. Plasma T4 concentrations increased approximately 2-fold on day 1, but decreased to initial levels on days 3 and 5. Changes in T4 secretion in vitro paralleled those in plasma T4 concentrations; T4 secretion increased 2-fold on day 1, and decreased to the pre-TSH levels on days 3 and 5. In contrast, T3 secretion increased throughout the experimental period. The T3/T4 ratio in thyroidal secretion in vitro was the same as that in thyroidal contents on days 0 and 1 of TSH infusion, but the former was significantly greater than the latter on days 3 and 5. PTU (5.9 X 10(-5) M), a known inhibitor of T4 deiodination, added to the incubation media did not affect T4 secretion on days 0 and 1, but increased T4 secretion on days 3 and 5 to the level of day 1, but did not affect T3 secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prolonged administration of thyrotrophin on serum concentration, release and synthesis of thyroid hormones in mice.

Mice were injected sc with TSH (0.5 U) at 12 h intervals for 5 days. Groups of mice were sacrificed daily to determine serum T4 and T3 concentrations, 4 h thyroidal 125I uptake, distribution of 125I among thyroidal iodoamino acids, and thyroidal content of T4 and T3. Serum T4 and T3 concentrations increased significantly after the initial injection of TSH and gradually decreased thereafter, reaching initial levels on the 3rd and 4th days, respectively. In contrast to serum hormone levels, thyroidal 125I uptake, incorporation of 125I into T4 and T3 increased significantly on the first day and remained elevated throughout the period of TSH-treatment. Thyroidal T4 content expressed as microgram/mg weight of tissue decreased significantly on the first day and thereafter remained constant. Thyroidal T3 content did not change significantly throughout the experimental period. The differences between thyroidal synthesis and thyroidal contents of T4 and T3 strongly suggest that thyroid hormone secretion is being continuously stimulated. Transient increases in serum T4 and T3 concentrations are probably due to a gradual increase in the rate of peripheral degradation of thyroid hormones. These results suggest that TSH-induced refractoriness in thyroidal iodine metabolism does not appear to exist, at least when TSH is given in vivo for 5 days.