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Background The World Trade Center (WTC) general responder cohort (GRC) was exposed to environmental toxins possibly associated with increased risk of developing autoimmune conditions. Objectives Two study designs were used to assess incidence and risks of autoimmune conditions in the GRC. Methods Three clinically trained professionals established the status of possible GRC cases of autoimmune disorders adhering to diagnostic criteria, supplemented, as needed, by specialists' review of consenting responders' medical records. Nested case-control analyses using conditional logistic regression estimated the risk associated with high WTC exposure (being in the 9/11/2001 dust cloud or ≥median days' response worked) compared with low WTC exposure (all other GRC members'). Four controls were matched to each case on age at case diagnosis (±2 years), sex, race/ethnicity, and year of program enrollment. Sex-specific and sensitivity analyses were performed. GRC age- and sex-adjusted standardized incidence ratios (SIRs) were compared with the Rochester Epidemiology Project (REP). Complete REP inpatient and outpatient medical records were reviewed by specialists. Conditions meeting standardized criteria on ≥2 visits were classified as REP confirmed cases. Results Six hundred and twenty-eight responders were diagnosed with autoimmune conditions between 2002 and 2017. In the nested case-control analyses, high WTC exposure was not associated with autoimmune domains and conditions (rheumatologic domain odds ratio [OR] = 1.03, 95% confidence interval [CI] = 0.77, 1.37; rheumatoid arthritis OR = 1.12, 95% CI = 0.70, 1.77). GRC members had lower SIR than REP. Women's risks were generally greater than men's. Conclusions The study found no statistically significant increased risk of autoimmune conditions with WTC exposures.

Introduction: Lymphocytic hypophysitis is an uncommon inflammatory disorder of the pituitary gland. Peripartum women are most often affected, but it can be seen in a wide range of patients. Patients can present with pituitary dysfunction or mass effect symptoms, making it difficult to differentiate from a pituitary adenoma. Pituitary apoplexy is an acute syndrome due to hemorrhage into the pituitary gland causing headache, visual deficits, and hypoadrenalism. We present a case of a woman with a pituitary mass presenting with symptoms mimicking pituitary apoplexy, in whom surgical pathology later revealed lymphocytic hypophysitis without evidence of hemorrhage. Clinical Case: A 27-year-old non-pregnant female presented with severe headaches, nausea, vomiting, and diplopia for four days. A presumed pituitary macroadenoma was diagnosed two years previously during a workup for irregular menses. An emergency evaluation with a CT angiogram of the head showed enhancement at the superior aspect of and surrounding the pituitary gland. MRI of the pituitary revealed an enhancing 17 x 17 mm sellar and suprasellar mass compressing the optic chiasm, without evidence of the normal pituitary posterior bright spot. Visual field testing was normal. She was referred for transsphenoidal resection of the pituitary mass due to persistent headaches, optic chiasm impingement, and suspicion of pituitary apoplexy. Intraoperatively, there was no evidence of hemorrhage. Central diabetes insipidus and hypothyroidism developed in the post-operative period. She was discharged on hydrocortisone replacement therapy (20 mg in the morning, 10 mg in the afternoon). An outpatient random cortisol level of 1.2 mcg/dL (reference: 6.7 - 22.6 mcg/dL) while off hydrocortisone for twenty-four hours confirmed hypocortisolism. Surgical pathology showed moderate lymphocytic infiltrate and focal germinal centers in the adenohypophysis consistent with lymphocytic hypophysitis. Conclusion: Although lymphocytic hypophysitis is well-described in the literature, its association with symptoms suggesting pituitary apoplexy has been reported only rarely. This atypical case shows that lymphocytic hypophysitis can present with acute symptoms mimicking pituitary apoplexy. The case highlights the difficulties in recognizing lymphocytic hypophysitis prior to surgery and emphasizes the need to consider the diagnosis in patients presenting with pituitary masses and/or symptoms of pituitary apoplexy.

Background: Multiple Endocrine Neoplasia Syndrome Type 2 (MEN2) is an inherited endocrine disorder characterized by the development of pheochromocytoma, medullary thyroid carcinoma (MTC) and parathyroid neoplasia. MEN2 is autosomal dominant and occurs from activating missense variants in the RET proto-oncogene. The estimated prevalence of MEN2 is thought to be 1 per 30,000 in the general population, and although rare, the identification of MEN2 can aid with early screening and prevention for patients and their families. Aim: The aim of our study was to investigate the prevalence and clinical manifestations of pathogenic RET variants in the multi-ethnic BioMe Biobank. Methods: We used exome sequencing and electronic health record (EHR) data from BioMe Biobank participants, who are recruited from primary care and specialty clinics across a single U.S. Health System. We evaluated exome sequence data from 30,000 BioMe participants for RET variants designated as pathogenic for MEN2 according to the clinical genetics database ClinVar. We reviewed EHR data for carriers of pathogenic RET variants. Results: In the BioMe Biobank, 5 ClinVar pathogenic variants were identified in the RET gene. Fifteen participants were heterozygous carriers of these variants; 5 were of self-reported African ancestry, 5 of Hispanic/Latino ancestry, 2 of European ancestry, and 3 of other or unknown ancestry. The age range of carriers was 23-78 years, and 60% were female. The estimated prevalence of pathogenic RET variant carriers in BioMe was ~1 in 2000. Based on EHRs, only 3 carriers (20%) were identified from usual clinical care as having the diagnosis of MEN2A. All 3 carriers with diagnosed MEN2A had the 10:43114500:T:C variant (rs75076352) and had a history of MTC and pheochromocytoma. One of the 3 carriers had a history of elevated parathyroid hormone levels and renal calculi without hypercalcemia. Two of the 3 carriers had a documented family history of MEN2A. Of the 12 pathogenic RET variant carriers without known MEN2, 9 (75%) were diagnosed with hypertension. 7 (58%) carried the 10:43119548:G:A variant (rs79658334). Of these 7 carriers, one had a thyroid nodule, three had autoimmune thyroid disease, one had an adrenal cortical adenoma with primary hyperaldosteronism and hypokalemic periodic paralysis, and two had no known endocrine conditions. Conclusions: These results from the BioMe Biobank reveal a higher prevalence of pathogenic RET variants than previously recognized. Carriers of pathogenic RET variants demonstrate highly variable expressivity for traits for which earlier diagnoses might improve outcomes; these findings have implications for cascade testing of family members. Genomic screening for pathogenic RET variants will likely improve our understanding of MEN2 on a more molecular basis.

Summary objective To determine the utility of ultrasonography for the preoperative localization of enlarged parathyroid glands in primary hyperparathyroidism, and to compare this method with 99mtechnetium sestamibi scintigraphy. design The results of ultrasonography for localization of enlarged parathyroid glands were determined in 120 consecutive patients with primary hyperparathyroidism and compared with findings at surgery (n = 86) and with the results of 99mtechnetium sestamibi scintigraphy (n = 99). patients All patients had biochemically documented primary hyperparathyroidism based on elevated serum calcium and ‘intact’ parathyroid hormone measured by immunoassay. Patients with prior parathyroid surgery or secondary hyperparathyroidism were excluded. measurements High-resolution ultrasonography was performed by a single observer. 99mTechnetium sestamibi scintigraphy was performed using early and delayed (2-h) views, and correlated with simultaneous thyroidal 123I uptake in most patients. results Ultrasonography detected putative enlarged parathyroid glands in 92 of 120 unselected patients (77%). It correctly predicted surgical findings in 64 of 86 patients undergoing surgery (74%), including 61 of 72 patients with solitary eutopic parathyroid adenomas (84%), but only two of eight patients with solitary ectopic adenomas, and only one of six patients with multigland parathyroid disease. Sestamibi scintigraphy was positive in 87 of 99 unselected patients (88%), a higher proportion than ultrasonography (P

En combinant l'information obtenue en preoperatoire sur la localisation des glandes et en peroperatoire, a partir du monitorage de la parathormone (PTH), on peut realiser une parathyroidectomie dite «ciblee». Pour ce faire, on a developpe de multiples approches, allant de l'exploration cervicale unilaterale (ECU) a la parathyroidectomie radioguidee (PR) et a la parathyroidectomie laparoscopique (PL). Le but de cette etude a ete d'evaluer l'efficacite de ces differentes approches dans la prise en charge de l'hyperparathyroidie primitive. Entre juin 1998 et novembre 2000, on a realise 110 interventions «ciblees» sur la parathyroide dans un centre medical universitaire. Tous les patients ont eu une scintigraphie au technetium-99m-sestamibi et/ou une echographie avant l'intervention. Le monitorage peroperatoire de la PTH a ete utilise dans tous les cas. Trente-sept patients ont eu une ECU, 59, une PR, et 14, une PL. Avec un suivi entre 1 et 24 mois, tous les patients ont ete gueris apres leur parathyroidectomie comme le laissait prevoir une reduction superieure a 50% du dosage peroperatoire de la PTH apres ablation de toutes les glandes hypersecretantes. Cent trois patients avaient un adenome solitaire (95%) et un patient avait un cancer de la parathyroide. Six patients (5%) avaient une maladie multiglandulaire, y compris quatre cas d'hyperplasie et deux patients porteurs d'un adenome double. Quatre-vingt-trois patients (75%) ont pu quitter l'hopital le jour de leur intervention. La localisation preoperatoire et l'utilisation du monitorage peroperatoire de la PTH permettent une approche «ciblee» dans le traitement de l'hyperparathyroidie primitive. Les chirurgiens endocrines devraient etre familiers avec toutes les techniques mini-invasives de la parathyroidectomie afin de pouvoir adapter l'approche operatoire a chaque cas individuel.

BACKGROUND Aberrant expression of the facilitative glucose transporter GLUT1 is found in a wide spectrum of epithelial malignancies. The authors describe an immunohistochemical study of GLUT1 expression in benign, borderline, and malignant ovarian epithelia. METHODS One hundred forty one formalin-fixed, paraffin-embedded sections were immunostained with rabbit anti-GLUT1 using the streptavidin-biotin method. The samples were as follows: 3 endometriotic cysts, 9 serous cystadenomas, 15 mucinous cystadenomas, 17 noninvasive borderline implants, 3 invasive borderline implants, and 3 endosalpingiosis. In addition, 35 borderline tumors (26 serous, 7 mucinous, 2 seromucinous) and 56 adenocarcinomas (50 serous, 4 endometrioid, 2 mucinous) were stained. RESULTS Benign serous and mucinous cystadenomas and endosalpingiosis were non-staining with GLUT1 antiserum. Twenty-eight of 35 borderline tumors (80%) stained positively, with weak to moderate (1-2+ out of 3) staining intensity and focal or patchy distribution. Seventeen noninvasive serous borderline implants were negatively stained; however, three invasive serous borderline implants were positively stained with GLUT1 antiserum. Fifty four of 56 ovarian carcinomas (96%) stained positively, with moderate to strong (2-3+ out of 3) intensity and multifocal distribution. CONCLUSIONS GLUT1 is a consistent marker of ovarian epithelial malignancy. GLUT1 staining is absent in benign ovarian epithelial tumors, and shows progressively more staining in invasive tumors as compared to borderline tumors. Anti-GLUT1 antibody may be useful in distinguishing invasive from noninvasive serous borderline implants. Cancer 2002;94:1078–82. © 2002 American Cancer Society. DOI 10.1002/cncr.10280

Fine needle aspiration (FNA) cytology is the best test for malignancy in thyroid nodules. However, cytologic interpretation of FNA specimens is often difficult, especially in the presence of indeterminate microfollicular cytologic patterns, which are thought to suggest follicular neoplasm (adenoma or carcinoma). To assess the risk of malignancy associated with specific cytologic patterns, we correlated preoperative FNA cytologic patterns (n = 484 reports including repeat aspirations) with final histological diagnoses for 368 surgical thyroid specimens obtained during the period 1994-1998. The overall prevalence of malignancy in the surgical specimens was 31% (113 cancers, including 96 papillary and 9 follicular carcinomas). For nodules with benign FNA cytologic diagnoses of nodular goiter and chronic thyroiditis there was a low risk of malignancy (6/99, or 6.1%). Nodules with indeterminate cytologic patterns in the absence of nuclear atypia (i.e., microfollicles without nuclear atypia) had a similarly low malignancy risk (3/46, or 6.5%). In contrast, 31/52 nodules with cytologic nuclear atypia consistent with follicular neoplasm were malignant (60%), including specimens with or without microfollicular cytology. Nodules with frankly malignant cytologic patterns were almost invariably cancer (54/55), and cytologic diagnoses of papillary carcinoma were confirmed at surgery in all 49 cases. These results indicate that indeterminate microfollicular cytologic patterns in the absence of nuclear atypia are associated with a low risk of malignancy, at least in this series. This finding suggests that many nodules with such microfollicular cytology might be managed conservatively with observation. In contrast, cytologic nuclear atypia consistent with a follicular neoplasm confers a high risk of cancer. In addition, frankly malignant cytologic diagnoses, especially papillary carcinoma, are highly reliable, and thus may be used as a guide for planning surgery appropriate for thyroid cancer.

Objective To review the role of ultrasonography in the detection and management of thyroid cancer Methods Viewpoints are presented on the appropriate applications and the advantages of ultrasonography, based on an extensive personal experience with more than 1,500 ultrasound examinations for assessment of thyroid nodules and for follow-up surveillance of patients with thyroid cancer. Results Ultrasonography is ideal for thyroid imaging because of the high echogenicity of thyroid tissue, the superficial site of the thyroid that allows the use of high- frequency transducers yielding high resolution, and the low expense compared with other techniques. In patients with a thyroid nodule, ultrasonography can assist in distinguishing benign from malignant disease. Ultrasound studies will characterize the presence of cystic versus solid elements, the degree of echogenicity of solid elements, the existence of calcifications, and the regularity and definition of the nodule borders. Although individual sonographic features of thyroid nodules are not specific for benign or malignant lesions, a constellation of typical features has more diagnostic value. Hypoechogenicity, poorly defined irregular margins, and microcalcifications are characteristics that should increase the index of suspicion for a malignant nodule. Cytologic examination of fine- needle aspirates is the optimal diagnostic test, and ultrasonographic guidance for performance of the aspiration biopsy is often helpful and sometimes critical. Ultrasonography is also useful for detection of cervical lymph node metastatic lesions. Lymph nodes involved with metastatic thyroid cancer tend to become rounded and bulging, and they lose their hilar echoes as their structure becomes disrupted. Conclusion Because of its high resolution and relatively reasonable cost, ultrasonography is valuable in the diagnosis and management of thyroid cancer. (Endocr Pract. 2000;6:396-400)

BACKGROUND Malignant cells exhibit increased glycolytic metabolism, and in many cases increased glucose transporter gene expression. The authors hypothesized that GLUT1 glucose transporter expression is increased in colorectal carcinoma, and that the degree of expression might have prognostic significance. METHODS GLUT1 glucose transporter immunostaining was studied in normal colon and benign colon adenomas and in 112 colorectal carcinomas from patients for whom long term clinical outcome was known. RESULTS GLUT1 immunostaining was absent in normal colorectal epithelium and tubular adenomas, and absent or only weakly apparent in tubulovillous adenomas. The majority of carcinomas (101 of 112; 90%) had GLUT1 immunostaining. Tumors from 92 patients had low GLUT1 expression ( 50% of cells were GLUT1 positive) and 9 of these patients (45%) died of disease during follow-up. Disease specific mortality was greater in patients with high GLUT1 tumors (relative risk of 2.4; P = 0.02). In a multivariate analysis to assess whether high GLUT1 staining correlated with increased mortality independently of Dukes stage, the risk of death from colon carcinoma in the group with high GLUT1 staining was 2.3 times that in the group with low GLUT1 staining, a difference that approached statistical significance (P = 0.07). CONCLUSIONS GLUT1 glucose transporter expression is associated strongly with neoplastic progression in the colon, and assessment of the extent of GLUT1 immunostaining in colorectal carcinoma identifies patients with a poorer prognosis. Cancer 1998;83:34-40. © 1998 American Cancer Society.

To test the hypothesis that glucocorticoids inhibit muscle glucose transport apart from changes in early insulin-signaling events, we determined the effect of glucocorticoid treatment on the activation of glucose transport by both insulin and non-insulin-related stimuli (insulin-like growth factor [IGF] I and hypoxia) in rat skeletal muscle. Male Sprague-Dawley rats were treated with dexamethasone (Dex) (0.8 mg/kg for 2 days) and compared with pair-fed controls. 2-[3H]deoxyglucose (2-[3H]DG) uptake in isolated soleus muscles was measured under conditions in which uptake reflects glucose transport activity. In control muscles, 2-[3H]DG uptake was stimulated 10-fold by insulin (10 nmol/l) or IGF-I (50 nmol/l) and sixfold by hypoxia. Dex treatment decreased 2-[3H]DG uptake at all concentrations of insulin tested, reducing maximal insulin-stimulated 2-[3H]DG uptake by 41 ± 11% (mean ± SE, P < 0.05) and basal 2-[3H]DG uptake by 38 ± 6% (P < 0.01). Dex treatment also inhibited 2-[3H]DG uptake at all concentrations of IGF-I tested, reducing maximal IGF-I-stimulated 2-[3H]DG uptake by 29 ± 2% (P < 0.01), and decreased hypoxia-stimulated 2-[3H]DG uptake by 61% (P < 0.01). Dex treatment increased soleus GLUT4 protein content by 11%. Thus, Dex treatment reduces basal glucose transport and decreases the maximal response of skeletal muscle glucose transport to insulin, the related hormone IGF-I, and the non-insulin-related stimulus hypoxia. These findings support the hypothesis that, in addition to altering early insulin-signaling events, glucocorticoids may also act by inhibiting the glucose transport system, per se, perhaps by affecting GLUT4 subcellular trafficking.

We have previously reported that the stimulation of glucose transport by thyroid hormone in the rat liver-derived ARL 15 cell line is attributable, at least in part, to increased abundance of cellular glucose transporters with a corresponding increase in the mRNA coding for the GLUT1 glucose transporter isoform. To elucidate further the mechanism by which thyroid hormone increases glucose transport, we examined the time-course of the effect of L-triiodothyronine (T3) on 3H-2-deoxyglucose uptake, GLUT1 protein abundance, and GLUT1 mRNA abundance in ARL 15 cells. At 6 h of T3 treatment, 3H-2-deoxyglucose uptake was increased by 40 +/- 11%, whereas the abundance of GLUT1 protein in cell extracts had not yet changed at this time. At 48 h, GLUT1 protein was increased by 58 +/- 10%, whereas 3H-2-deoxyglucose uptake at this time was increased by 116 +/- 14%. GLUT1 mRNA levels rose within 4 h of T3 treatment, preceding the increase in GLUT1 protein, and more than doubled by 24 h. In additional experiments to determine the mechanism by which T3 increases GLUT1 mRNA, T3 treatment for 48 h increased the rate of transcription of the GLUT1 gene, determined by nuclear run-on analysis, by 55 +/- 11%. T3 treatment did not significantly alter the half-life of GLUT1 mRNA. In the presence of inhibitors of protein synthesis, GLUT1 mRNA increased at 6 h (5-7-fold), but there was no further induction of this mRNA by T3 in the presence of these inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

The thyroidal response of pregnant patients with established Hashimoto's thyroiditis remains poorly described. The aim of this study was to determine the impact of pregnancy on Hashimoto's thyroiditis as revealed by changes in postpregnancy levothyroxine requirements.We performed a retrospective study of 799 hypothyroid patients in a university hospital. We reviewed the clinical records and selected a group of well-documented pregnant (n = 34) and nonpregnant (n = 32) hypothyroid women for study. We reviewed levothyroxine intake and serum thyrotropin (TSH) levels during three consecutive 9-month time intervals that were immediately before, during, and after pregnancy. We compared the percent change in levothyroxine dose between the prepregnancy level and each trimester during and after pregnancy.There were two patterns of levothyroxine supplementation during gestation. In pattern 1 (n = 11) there was either no change or a single levothyroxine dose increase with no subsequent changes in each trimester (T1 = T2 = T3). In pattern 2 (n = 18), multistep levothyroxine dose increases were required throughout pregnancy (T1T2T3) to maintain desired TSH levels (2.0 mU/L). Women with pattern 2 had mean TSH levels during gestation that differed significantly from pattern 1 (2.8 +/- 0.5 vs. 1.3 +/- 0.1 mU/L respectively; p0.03). Further, in multivariate logistic regression, women with pattern 2 were 62 times more likely than women with pattern 1 to have a levothyroxine dose at least 20% above baseline at 3 months postpartum (p = 0.04).We showed that50% of hypothyroid women with Hashimoto's thyroiditis experienced an increase in levothyroxine requirements in the postpartum compared to pregestational doses. This pattern of enhanced levothyroxine need was most likely dependent on the preexisting thyroid functional reserve and postpartum progression of autoimmune destruction.

The enhancement of metabolic rate by thyroid hormone in target tissues is accompanied by increased glucose utilization, which in skeletal muscle and many other tissues is regulated at the level of membrane transport. To elucidate the role of thyroid hormone as a regulator of glucose transport in skeletal muscle, we have examined its effects on the expression of the muscle/fat (insulin-regulatable) glucose transporter, a distinct glucose transporter isotype whose expression is limited to insulin-sensitive tissues and which appears to be the major glucose transport protein in skeletal muscle. Treatment of hypothyroid rats with L-T3 (T3; 100 micrograms/100 g BW.day for 6 days) increased the abundance of the muscle/fat glucose transporter protein in crude membranes from hindlimb muscle, assessed by immunoblotting, to 145 +/- 8% of the control value in animals fasted for 17-20 h before death and to 159 +/- 16% of the control value in animals fed ad libitum (mean +/- SE). In purified plasma membranes, this effect of thyroid hormone was greater (208 +/- 23% and 219 +/- 13% of control in fasted and fed animals, respectively). Similar increases were found in an intracellular membrane fraction. Levels of muscle/fat glucose transporter mRNA were also increased in hindlimb muscle from the T3-treated rats, to 261 +/- 17% and 316 +/- 23% of control values in fasted and fed animals, respectively. In contrast, the erythroid glucose transporter protein and its mRNA, which are only weakly expressed in skeletal muscle but strongly expressed in brain, were not substantially increased by T3 treatment in either tissue. In experiments comparing hypothyroid, euthyroid, and chronically T4-treated animals, muscle/fat glucose transporter protein and mRNA abundance in skeletal muscle were also found to be dependent on thyroid status. Thyroid hormone may, thus, be an important regulator of the muscle/fat glucose transporter in skeletal muscle.

To determine the utility of ultrasonography for the preoperative localization of enlarged parathyroid glands in primary hyperparathyroidism, and to compare this method with (99m)technetium sestamibi scintigraphy.The results of ultrasonography for localization of enlarged parathyroid glands were determined in 120 consecutive patients with primary hyperparathyroidism and compared with findings at surgery (n = 86) and with the results of (99m)technetium sestamibi scintigraphy (n = 99).All patients had biochemically documented primary hyperparathyroidism based on elevated serum calcium and 'intact' parathyroid hormone measured by immunoassay. Patients with prior parathyroid surgery or secondary hyperparathyroidism were excluded.High-resolution ultrasonography was performed by a single observer. (99m)Technetium sestamibi scintigraphy was performed using early and delayed (2-h) views, and correlated with simultaneous thyroidal 123I uptake in most patients.Ultrasonography detected putative enlarged parathyroid glands in 92 of 120 unselected patients (77%). It correctly predicted surgical findings in 64 of 86 patients undergoing surgery (74%), including 61 of 72 patients with solitary eutopic parathyroid adenomas (84%), but only two of eight patients with solitary ectopic adenomas, and only one of six patients with multigland parathyroid disease. Sestamibi scintigraphy was positive in 87 of 99 unselected patients (88%), a higher proportion than ultrasonography (P0.05), reflecting superior sensitivity for the detection of ectopic parathyroid adenomas. For 74 patients undergoing parathyroid surgery who underwent both imaging tests there was no statistically significant difference between ultrasonography and sestamibi scintigraphy in ability to correctly predict surgical findings (74%vs. 82%, respectively) or in positive predictive value (93%vs. 90%, respectively). However, sestamibi scintigraphy was clearly more sensitive for ectopic parathyroid adenomas, providing correct localization in 8/8 cases. When one test was negative, testing with the second method was usually positive, improving the likelihood of a positive result to 98% when both tests were employed.Ultrasonography can be a sensitive and accurate method for preoperative localization of enlarged parathyroid glands in primary hyperparathyroidism, comparable in overall utility to sestamibi scintigraphy. These results suggest that a strategy of initial testing with one or the other method, followed by the alternate imaging test if the first test is negative, would provide correct parathyroid imaging in most patients without prior parathyroid surgery.

Background: Improvements in the accuracy of preoperative localization and the availability of the rapid parathyroid hormone assay have permitted minimally invasive parathyroidectomy in patients with primary hyperparathyoidism. Hypothesis: The use of intraoperative radioguidance is beneficial during targeted parathyroid operations. Design: A retrospective analysis of a prospective database of patients. Setting: Tertiary care referral center. Patients: During a 2 1 ⁄2-year period, 130 patients underwent minimally invasive, targeted parathyroidectomy with intraoperative monitoring of the parathyroid hormone level. Of these, 60 patients underwent radioguided parathyroidectomy. Prior to surgery, a solitary parathyroid adenoma was visualized on technetium Tc 99m sestamibi scintigraphy in all patients selected for radioguided parathyroidectomy. A gamma probe was used to guide the surgical dissection. Results: All patients were cured following radioguided parathyroidectomy. In 29 patients (48%), the probe provided confusing or inaccurate information; however, a unilateral neck exploration with excision of a parathyroid adenoma was successfully completed in each of these patients. Forty-three cases were completed under local anesthesia and 85% were discharged home on the same day of surgery. There was 1 temporary recurrent laryngeal nerve palsy. Conclusion: In the era of improved preoperative localization and intraoperative parathyroid hormone monitoring, the routine use of radioguidance is not recommended during parathyroidectomy.

Aberrant expression of the facilitative glucose transporter GLUT1 is found in a wide spectrum of epithelial malignancies. The authors describe an immunohistochemical study of GLUT1 expression in benign, borderline, and malignant ovarian epithelia.One hundred forty one formalin-fixed, paraffin-embedded sections were immunostained with rabbit anti-GLUT1 using the streptavidin-biotin method. The samples were as follows: 3 endometriotic cysts, 9 serous cystadenomas, 15 mucinous cystadenomas, 17 noninvasive borderline implants, 3 invasive borderline implants, and 3 endosalpingiosis. In addition, 35 borderline tumors (26 serous, 7 mucinous, 2 seromucinous) and 56 adenocarcinomas (50 serous, 4 endometrioid, 2 mucinous) were stained.Benign serous and mucinous cystadenomas and endosalpingiosis were non-staining with GLUT1 antiserum. Twenty-eight of 35 borderline tumors (80%) stained positively, with weak to moderate (1-2+ out of 3) staining intensity and focal or patchy distribution. Seventeen noninvasive serous borderline implants were negatively stained; however, three invasive serous borderline implants were positively stained with GLUT1 antiserum. Fifty four of 56 ovarian carcinomas (96%) stained positively, with moderate to strong (2-3+ out of 3) intensity and multifocal distribution.GLUT1 is a consistent marker of ovarian epithelial malignancy. GLUT1 staining is absent in benign ovarian epithelial tumors, and shows progressively more staining in invasive tumors as compared to borderline tumors. Anti-GLUT1 antibody may be useful in distinguishing invasive from noninvasive serous borderline implants.

Cytologic examination of fine needle aspiration (FNA) specimens from thyroid nodules is the key test for the evaluation of thyroid nodules, and the results are critical in the selection of patients with nodules for thyroid surgery. Although needle placement for FNA is traditionally and most commonly guided by nodule palpation alone, the widespread availability of thyroid ultrasonography has made possible a technical refinement of this technique, needle placement under ultrasonographic guidance. Ultrasound-guided FNA is often valuable, and sometimes essential, in obtaining accurate diagnostic material. This chapter reviews the role of ultrasound-guided fine needle aspiration (UG FNA) in the diagnosis of thyroid nodules.

Malignant cells exhibit increased rates of glycolysis and glucose uptake, the latter of which is mediated by glucose transport proteins. Because several types of cancer have been shown to express high levels of the GLUT1 glucose transporter isoform, we hypothesized that expression of GLUT1 might distinguish malignant from benign thyroid tissue. Archival thyroid tissue obtained at surgery was immunostained for GLUT1 protein. There were 38 benign cases (24 follicular adenoma, 1 Hurthle cell adenoma, 8 nodular goiter, 3 Hashimoto's thyroiditis, 2 Graves' disease) and 28 cases of thyroid cancer (17 papillary and its follicular variant, 6 follicular, 1 Hurthle cell, 2 anaplastic, 2 medullary). Normal thyroid tissue adjacent to nodules showed no thyrocyte staining in any case. No GLUT1 staining was seen in thyrocytes in benign nodular tissue, except for a single case of Hashimoto's thyroiditis in which a few Hurthle cells showed weak staining. Among the thyroid cancers, 13 of 28 (46%) showed tumor cell GLUT1 staining in at least some areas. This included 9 of 17 cases of papillary carcinoma and its follicular variant, 2 of 6 cases of follicular carcinoma and 2 of 2 cases of anaplastic carcinoma. Tumor cell GLUT1 staining was seen in two patterns: circumferential plasma membrane staining focally within the tumor, or asymmetric staining of the basilar aspect of tumor cells adjacent to stroma in some cases of papillary carcinoma. We conclude that GLUT1 expression is frequently detectable by immunostaining in thyroid cancer, but not in benign nodules or normal thyroid. GLUT1 expression may be a clinically useful molecular marker for thyroid cancer.

The stimulation of glucose transport by 3,5,3'-triiodo-L-thyronine (T3) in the liver-derived ARL 15 cell line is only partly attributable to increased GLUT-1 glucose transporter gene expression. To test the hypothesis that T3 increases the partitioning of GLUT-1 to the cell surface, we quantitated surface GLUT-1 using the photolabel ATB-[3H]BMPA. In control cells only approximately 20% of total cellular GLUT-1 was present at the cell surface. T3 treatment (100 nM) for 6 h increased the rate of 2-deoxy-[3H]glucose (2-DG) uptake by 30, 92, and 95% in three experiments and increased surface GLUT-1 photolabeling by 17, 81, and 72%, respectively, with no increase in total cellular GLUT-1. T3 treatment for 48 h increased 2-DG uptake by 143, 172, and 216% in three experiments and increased cell surface GLUT-1 photolabeling by 88, 161, and 184%, respectively, with smaller increases in total cellular GLUT-1. T3 treatment for 48 h thus increased the fraction of cellular GLUT-1 at the plasma membrane from 21 +/- 2 to 35 +/- 3% (SE). We conclude that most of the early (6-h) stimulation of glucose transport by T3 in ARL 15 cells is mediated by an increase in the partitioning of GLUT-1 to the plasma membrane. With more chronic T3 treatment (48 h), the enhanced surface partitioning of GLUT-1 is persistent and is superimposed on an increase in total cellular GLUT-1, accounting for a further increase in glucose transport.

In skeletal muscle, the main site of insulin-mediated glucose disposal, the major muscle glucose transporter GLUT4 is induced by thyroid hormone. To test the hypothesis that thyroid hormone alters muscle glucose transport, we examined the effect of L-triiodothyronine (T3) on glucose transport and GLUT4 protein content in isolated rat skeletal muscles. Euthyroid rats were treated with or without T3 for 3 days, and [3H]2-deoxy-D-glucose (2-DG) uptake in soleus and extensor digitorum longus (EDL) muscles was measured under conditions in which transport was rate limiting for uptake in the absence or presence of 10 nmol/l insulin. In control animals, insulin stimulated 2-DG uptake sevenfold in soleus and fivefold in EDL. T3 treatment increased basal 2-DG uptake in soleus and EDL by 115 ± 29% and 136 ± 23%, respectively, and increased insulin-stimulated 2-DG uptake in soleus and EDL by 55 ± 9 and 42 ± 12%, respectively. Immunoblot analysis revealed that T3 treatment increased GLUT4 protein content in soleus by 43 ± 6% and in EDL by 56 ± 13%. These data demonstrate that thyroid hormone increases basal and insulin-stimulated glucose transport in skeletal muscle. The percentage increase in insulin-stimulated transport in T3-treated muscles is similar to the increase in GLUT4 protein content, whereas the percentage change in basal transport greatly exceeds the change in GLUT4. Thus, increased insulin-stimulated glucose transport in T3-treated muscle can be accounted for by the induction of GLUT4 protein. However, increased basal glucose transport in T3-treated muscle must reflect additional mechanisms, such as increased subcellular partitioning of GLUT4 to plasma membrane.

The extent to which the glucose transport system in hepatocytes is regulated in states of altered hepatic glucose metabolism is unclear. Because thyroid hormone is known to increase hepatic glucose output, we hypothesized that thyroid hormone might up-regulate expression of the principal hepatic glucose transporter, GLUT2, facilitating increased glucose efflux across the hepatocyte plasma membrane. GLUT2 protein concentration in crude liver membranes was twice as high in chronically hyperthyroid vs. hypothyroid animals, with intermediate levels in euthyroid controls. Similar results were obtained for total GLUT2 protein, measured in detergent extracts of liver. Northern analysis of total liver RNA demonstrated parallel changes in GLUT2 messenger RNA (mRNA) concentration per g tissue (hypothyroid, 76 +/- 6%; euthyroid, 100 +/- 11%; hyperthyroid, 158 +/- 12%; data expressed as percentage of mean euthyroid values). The daily administration of a large dose of T3 (100 micrograms/100 g BW) to hypothyroid rats caused a prompt increase in hepatic GLUT2 mRNA concentration (2.5-fold at 1 day), but only a modest and gradual change in hepatic GLUT2 protein concentration (+40% at 4 days), suggesting that the GLUT2 protein in liver may have a long half-life. We conclude that thyroid hormone regulates hepatic GLUT2 mRNA and protein expression. Up-regulation of GLUT2 protein expression by thyroid hormone may serve to facilitate increased hepatic glucose output. These results suggest that the hepatic GLUT2 glucose transporter, like the enzymes of gluconeogenesis and glycolysis, is indeed a regulatory target for hormones that control hepatic glucose metabolism.

Thiazolidine-2,4-diones, a new class of oral antihyperglycemic agents, have been shown to be effective in improving insulin sensitivity in a number of animal models of insulin resistance, and recent investigation has suggested that the mechanism of action of these agents may include upregulation of the GLUT4 (insulin-regulatable) glucose transporter. We studied the efficacy of two of these agents, pioglitazone and englitazone, in preventing glucocorticoid-induced insulin resistance in rats, and examined the potential role of changes in GLUT4 expression in their action in skeletal muscle. Rats were treated with 0.1 mg/d dexamethasone for 6 to 7 days with or without either pioglitazone (10 mg/kg/d) or englitazone (50 mg/kg/d). Both thiazolidinediones decreased the elevated fasting serum glucose and insulin levels in dexamethasone-treated animals. Dexamethasone treatment alone decreased insulin-stimulated 2-deoxyglucose uptake into isolated soleus muscles to 35% of control values. The addition of pioglitazone or englitazone increased insulin-stimulated 2-deoxyglucose uptake by 74% and 57%, respectively. Whereas dexamethasone treatment alone increased GLUT4 protein content in rat soleus muscle by 25%, additional treatment with pioglitazone or englitazone did not further significantly alter GLUT4 levels. We conclude that thiazolidinediones enhance insulin responsiveness in skeletal muscle during glucocorticoid treatment, but their mode of action in this setting is not via upregulation of GLUT4 expression.

The tissue distribution of the GLUT3 glucose transporter protein was examined in human tissues using a rabbit antiserum directed against the C-terminal peptide sequence of human GLUT3. This anti-serum was shown to recognize the human GLUT3 protein in Chinese hamster ovary cells transfected with GLUT3 cDNA and to immunoprecipitate an authentic glucose transport protein in brain and testis membranes, as assessed by glucose-inhibitable photolabeling with [3H] cytochalasin-B. The GLUT3 protein, migrating with an apparent mol wt of approximately 48 kilodaltons, was strongly expressed in brain and testis membranes as well as in spermatozoa. It was not detectable in membranes from erythrocytes, adipocytes, heart, skeletal muscle, liver, kidney, spleen, thyroid, and prostate. Very low levels may be present in placenta. In brain, GLUT3 protein was strongly expressed in grey matter regions and was only weakly expressed in white matter, suggesting that it may be important in providing glucose to regions of high metabolic activity, i.e. to areas associated with synaptic transmission. None was found in peripheral (femoral) nerve. It appeared to be stable for up to 47 h in autopsy brain tissue kept at 4 C. The tissue distribution of human GLUT3 protein thus appears to be highly restricted (brain and testis/spermatozoa), in contrast with a previous report. Its function may be to provide a high affinity glucose transport system in cells that are highly dependent on glucose as a fuel source.

Since thyroid hormone stimulates cardiac metabolism, for which glucose is an important fuel, we examined the effects of thyroid hormone on glucose transporter gene expression in rat heart. Treatment of hypothyroid animals with T3 for up to 6 days caused a 2-fold increase in GLUT4 mRNA at 1 day, and a 4-fold increase at 6 days (per unit DNA). GLUT4 protein, however, was not increased. In contrast, GLUT1 mRNA was transiently decreased by T3 treatment at 1 and 3 days, but returned to normal by 6 days. Concomitantly, GLUT1 protein decreased to 18% of the control value at 6 days. In chronically hypothyroid or hyperthyroid rats, GLUT4 mRNA varied directly with thyroid status, but GLUT4 protein was invariant, consistent with the acute effects of T3 treatment. Moreover, hypothyroidism increased GLUT1 mRNA and protein expression. We conclude that, in contrast to previous observations in skeletal muscle, GLUT4 protein content in rat heart is not altered by thyroid hormone. Cardiac GLUT1 expression is increased in hypothyroidism, and suppressed by thyroid hormone, at both the protein and mRNA levels. The observed discrepancy between GLUT4 mRNA and protein levels suggests that post-transcriptional regulatory events play a major role in GLUT4 expression in rat heart.

The diabetogenic effects of glucocorticoid excess are due in part to peripheral resistance to insulin. To test the hypothesis that glucocorticoid-induced peripheral insulin resistance might be attributable to a decreased number of glucose transporters, we examined the effects of dexamethasone treatment on the expression of the GLUT4 (insulin regulatable) glucose transporter in skeletal muscle, the major site of insulin-mediated glucose uptake. Dexamethasone treatment of rats (1 mg/day for 1 wk) induced hyperglycemia and hyperinsulinemia. At dosages of either 0.1 or 1 mg/day, insulin-stimulated 2-deoxyglucose uptake in isolated soleus muscle was reduced by greater than or equal to 50%, demonstrating the presence of insulin resistance in skeletal muscle. Immunoblots of crude membranes from deep quadriceps muscle showed that dexamethasone treatment (1 mg/day) increased the amount of GLUT4 protein by 84%. GLUT4 mRNA abundance was similarly increased when expressed per unit RNA but was unchanged when expressed on a DNA basis because the tissue RNA content was decreased by dexamethasone. In contrast to quadriceps, GLUT4 protein concentration in soleus and extensor digitorum longus extracts was not significantly increased by dexamethasone treatment. Because glucocorticoids cause selective atrophy of type IIb muscle fibers, which express relatively less GLUT4 protein, the apparent increase in GLUT4 content in quadriceps muscle from dexamethasone-treated animals may have resulted from inadvertent increased sampling of GLUT4-enriched type I and IIA fibers, caused by a glucocorticoid-induced decrease in the relative mass of the GLUT4-poor type IIb fibers. We conclude that glucocorticoids do not decrease GLUT4 content in skeletal muscle and that glucocorticoid-induced insulin resistance in this tissue is not due to suppression of glucose transporter gene expression.

We have studied regulation of the glucose transporter by thyroid hormone in ARL 15 cells, a thyroid hormone-responsive cell line derived from rat liver, T3 treatment (5 x 10(-8) M for 48 h) of confluent cell monolayers grown in thyroid hormone-deficient medium increased the rate of uptake of [3H] 2-deoxyglucose by 2.3 +/- 0.2-fold; this effect was half-maximal at a T3 concentration of 5 nM. The uptake of the nonmetabolizable hexose [3H]3-O-methylglucose was comparably increased, confirming a stimulation of glucose transport by thyroid hormone in these cells. In addition to enhancing glucose transporter activity, T3 increased the utilization of medium glucose to a similar degree. To elucidate the mechanism of the stimulation of glucose transport by T3, the number of glucose transporter units in crude membrane preparations was quantitated by measuring the glucose-inhibitable binding of [3H]cytochalasin-B. The Kd for specific (glucose-inhibitable) binding of [3H]cytochalasin-B was 50-60 nM, a value typical for nonhepatic glucose transporters. T3 treatment caused an increase in the glucose-inhibitable binding of this ligand that was similar in magnitude to the stimulation of [3H]2-deoxyglucose uptake (2.5 +/- 0.6-fold). Northern blot analysis of total cellular RNA using a cDNA probe for the rat brain glucose transporter showed a strong 2.9-kilobase hybridization signal after stringent washing, indicating that ARL 15 cells express the specific mRNA for this type of glucose transporter. T3 treatment increased the abundance of this mRNA by 2.3 +/- 0.2-fold. It is concluded that thyroid hormone stimulates glucose transport in ARL 15 cells, which express the brain type of glucose transporter. This effect is attributable at least in part, if not entirely, to an increase in the level of glucose transporter mRNA and an accompanying increase in the number of glucose transporter units. These findings suggest that thyroid hormone may be an important regulator of glucose transporter gene expression.

To elucidate the relationship between the stimulation of Na+ and K+ fluxes by thyroid hormone and the induction of the Na,K-ATPase, we performed a detailed comparison of the time courses of these hormonal effects in a rat liver cell line, clone 9. Stimulations of passive K+ efflux, passive Na+ influx, and ouabain-inhibitable K+ uptake were all evident within 6-12 h of exposure of cells to T3 (10(-7) M). The time course of the induction of Na,K-ATPase activity closely paralleled that of the increase in the rate of Na+ and K+ fluxes. The maximal stimulatory effects of T3 on ouabain-inhibitable K+ uptake and Na,K-ATPase activity at 72 h were +49% and +36%, respectively. Intracellular Na+ and K+ contents were virtually unchanged during these increases in ion fluxes and Na,K-ATPase activity, suggesting an efficient homeostatic adaptation to the augmented passive "leak" of Na+ and K+ down their transmembrane concentration gradients. T3 treatment for 72 h was also shown to stimulate both lactate production (+62%) and [3H]2-deoxyglucose uptake (+82%) in these cells. The onset of these effects appeared to precede that of the stimulation of Na+ and K+ fluxes, being detectable at 4 h. Neither these latter effects of T3 nor the stimulation of ouabain-inhibitable K+ uptake could be demonstrated when RNA or protein synthesis was inhibited by actinomycin D or cycloheximide, respectively. It is concluded that in clone 9 cells thyroid hormone causes increases in passive Na+ influx, passive K+ efflux, active Na,K transport, and Na,K-ATPase activity whose time courses are closely parallel.

Exposure of ARL 15 cells to medium containing reduced concentrations of K+ (0.65 mM) elicited a 50-100% increase in Na,K-ATPase activity. The inhibition by ouabain of both the basal and the induced enzyme conformed to a single-site model (KI = 1 x 10(-4) M). The low K+-induced increment in Na,K-ATPase activity was accompanied by an equivalent increase in the abundance of Na,K-pump sites estimated by ouabain-stabilized ("back-door") phosphorylation, such that the calculated catalytic turnover number of approximately 8000/min was minimally changed. Comparison of the dependence of ouabain-inhibitable K+ uptake on intracellular Na+ and on extracellular K+ concentrations in control and low K+-treated cells revealed no change in the respective half-maximal stimulatory concentrations for these cations, whereas the maximal rate of active K+ uptake in cells exposed to low external K+ increased by nearly 100%. The derived Hill coefficients for active K+ transport rate were also unchanged by the low K+ treatment (i.e. approximately 1.4 for extracellular K+ and 2.6 for intracellular Na+). Na,K-ATPase activity of basal and low K+-induced cells calculated from the measured maximal Na,K transport rate closely approximated the Na,K-ATPase activity measured enzymatically in unfractionated cell lysates under Vmax conditions, suggesting that all or most of the Na,K-ATPase enzymatic units present in both basal and stimulated states are functionally active. Northern blot analysis of RNA isolated from control cells indicated the presence of the Na,K-ATPase alpha-I isoform of the enzyme which increased by nearly 200% following incubation of the cells in low-K+ medium. By contrast, the alpha-II and alpha-III mRNAs were undetectable in either the basal or low K+-stimulated state. These results indicate that the Na,K-ATPase induced by incubation of ARL 15 cells in low-K+ medium is kinetically and functionally indistinguishable from the basal enzyme, and that only the alpha-I isoform is expressed under control and low-K+ conditions.

The effects of a low dose of T3 on passive cellular K+ efflux and Na,K-ATPase activity were studied in hypothyroid rat liver. Male Sprague-Dawley rats were rendered hypothyroid by 4 weeks of a low iodine diet with 0.5% NaClO4 added to the drinking water, and for the last 2 weeks of this period received daily sc injections of either T3 (1 microgram/100 g BW) or diluent alone. At the end of this time, both the passive efflux of 86Rb+ (a K+ analog) from liver slices isotopically prelabeled in vitro and Na,K-ATPase activity in liver homogenates were determined. The T3 treatment regimen resulted in a 55% increase in the 86Rb+ efflux rate constant (P less than 0.003), while, in contrast, Na,K-ATPase activity remained unchanged. These results show that T3, even at a low dose, enhances passive K+ efflux from liver slices and that, consistent with previous observations, this enhancement can occur in the absence of any detectable change in the number of Na,K pumps. Since the rate of Na,K pump function appears in general to be limited by the rate of passive cation permeation, rather than by Na,K pump number per se, these observations provide additional evidence that increased cation permeability may play a role in the stimulation of active cation transport by thyroid hormone.

Studies on the effect of T3 administration on the rate of passive potassium ion efflux from rat diaphragm have been carried out in an effort to define the mechanisms of the thermogenic effect of thyroid hormone. In particular, the effects of T3 on passive potassium ion movements have been examined in an attempt to distinguish between a primary stimulatory effect of thyroid hormone on active transport per se as opposed to one on passive cation permeability, in turn leading to the enhancement of steady-state ATP hydrolysis reflected in the thermogenic response. We show here that in rat diaphragm, a tissue in which previous studies have established a clear-cut thermogenic effect of thyroid hormone as well as an increase in ouabain-sensitive oxygen consumption and Na,K-ATPase activity, passive K+ efflux can be studied in vitro under conditions where fractional efflux rates are stable for prolonged periods of time and are amenable to simple and precise measurement. In this tissue, in which a primary stimulatio...

The effect of thyroid hormone treatment on the passive efflux of 42K+ from rat liver slices was studied to determine whether an increase in permeability might play a role in the known enhancement of active monovalent cation transport and Na,K-ATPase activity induced by thyroid hormone. Initial studies showed that the sc injection of 50 micrograms T3/100 g BW on 3 alternate days resulted in an 82% increase in the 42K+ passive efflux rate constant in liver slices and a 23% increase in the Na,K-ATPase activity of liver homogenates. Subsequent investigation of the relative time courses of these two hormonal effects showed that after a single injection of T3 the rate constant for 42K+ efflux increased within 6 h and reached a plateau between 24 and 48 h. In contrast, Na,K-ATPase activity was not augmented until 24 h and continued to rise between 24 and 48 h. These results suggest that an early increase in cation permeability (with resultant cation leak) may account for the known stimulatory effect of thyroid hormone on active monovalent cation transport in rat liver. The relatively late increase in Na,K-ATPase activity might then be regarded as an adaptive cellular response to increased passive cation fluxes rather than a direct effect of thyroid hormone. The magnitude and early onset of the effect of thyroid hormone treatment on cellular 42K+ efflux raise the possibility that an increase in passive cation permeability may be a proximal event in the mediation of thyroid hormone action.

A continuous cell line derived from rat liver (ARL 15) has been identified that responds to thyroid hormone with a stimulation of active Na,K transport. Stimulation of ouabain-inhibitable K+ uptake, which is half-maximal at a T3 concentration of 1.4 X 10(-10) M, is accompanied by corresponding increases in passive Na+ influx and in passive K+ efflux. The enhancement of Na+ and K+ fluxes by T3 is shown to be accompanied by smaller and equivalent increases both in enzymatically measured Na,K-ATPase activity and in maximal ouabain-sensitive Na,K transport in the presence of the Na+ ionophore monensin. The demonstration that both passive Na+ influx and passive fractional K+ efflux are simultaneously increased by T3 supports the earlier suggestion that the stimulation of active Na,K transport by thyroid hormone is attributable, at least in part, to an enhancement of rate-limiting passive Na+ and K+ fluxes by an increase in membrane permeability.

The Na+ ionophore monensin was used to study the Na+- and K+-dependence of ouabain-inhibitable 86Rb+ uptake in ARL 15 cells, a rat liver cell line. Graded concentrations of monensin rapidly induced incremental elevations of cellular Na+ that were stable for up to 2 h. In experiments in which cellular Na+ was thus “clamped” at various levels, the activation curve for ouabain-inhibitable 86Rb+ uptake as a function of intracellular Na+ was found to be steepest near basal Na+ levels (Hill coefficient approximately equal to 2.4), indicating that these cells can respond to relatively large changes in passive Na+ entry by increasing the race of Na-K pump function with only minimal increases in cellular Na+. Exposure of cells to monensin also permitted examination of the extracellular-K+ dependence of ouabain-inhibitable 86Rb+ uptake in the presence of saturating intracellular Na+ and yielded a Hill coefficient of approximately 1.5. The rate of ATP hydrolysis calculated from measurements of the maximal rate of ouabain-inhibitable 86Rb+ uptake in intact cells was similar to the enzymatic Vmax of the Na+-K+-ATPase in cell lysates, suggesting that the Na+-K+-ATPase activity in these broken-cell preparations closely reflects the functional transport capacity of the Na-K pump.

Exposure of ARL 15 cells, an established line from adult rat liver, to concentrations of external K+ below 1 mM caused a rapid fall in intracellular K+ and a corresponding rise in intracellular Na+ that became maximal within 12 h. Upon continued exposure to low external K+, these initial changes were followed by a striking recovery such that, by 24 h, intracellular Na+ and K+ concentrations approached their control values. Concomitant with this recovery, there was a substantial increase in Na,K-ATPase specific activity that was detectable at 12 h and maximal at 24 h. After restoration of the external K+ concentration, the elevated level of enzyme activity showed little change for at least 24 h. In contrast, restoration of external K+ resulted in a rapid rise in intracellular K+ and a fall in Na+ such that within 30 min the Na+/K+ ratio was lower than in control cells. This overshoot, together with a demonstrated increase in active 86Rb+ uptake under "Vmax" conditions, confirms that the enhancement in Na,K-ATPase specific activity in response to low external K+ represents an increase in functional Na,K pumping capacity.