Ralph R. Cavalieri

Comparison of administration of recombinant human thyrotropin with withdrawal of thyroid hormone for radioactive iodine scanning in patients with thyroid carcinoma.

BACKGROUND To detect recurrent disease in patients who have had differentiated thyroid cancer, periodic withdrawal of thyroid hormone therapy may be required to raise serum thyrotropin concentrations to stimulate thyroid tissue so that radioiodine (iodine-131) scanning can be performed. However, withdrawal of thyroid hormone therapy causes hypothyroidism. Administration of recombinant human thyrotropin stimulates thyroid tissue without requiring the discontinuation of thyroid hormone therapy. METHODS One hundred twenty-seven patients with thyroid cancer underwent whole-body radioiodine scanning by two techniques: first after receiving two doses of thyrotropin while thyroid hormone therapy was continued, and second after the withdrawal of thyroid hormone therapy. The scans were evaluated by reviewers unaware of the conditions of scanning. The serum thyroglobulin concentrations and the prevalence of symptoms of hypothyroidism and mood disorders were also determined. RESULTS Sixty-two of the 127 patients had positive whole-body radioiodine scans by one or both techniques. The scans obtained after stimulation with thyrotropin were equivalent to the scans obtained after withdrawal of thyroid hormone in 41 of these patients (66 percent), superior in 3 (5 percent), and inferior in 18 (29 percent). When the 65 patients with concordant negative scans were included, the two scans were equivalent in 106 patients (83 percent). Eight patients (13 percent of those with at least one positive scan) were treated with radioiodine on the basis of superior scans done after withdrawal of thyroid hormone. Serum thyroglobulin concentrations increased in 15 of 35 tested patients: 14 after withdrawal of thyroid hormone and 13 after administration of thyrotropin. Patients had more symptoms of hypothyroidism (P<0.001) and dysphoric mood states (P<0.001) after withdrawal of thyroid hormone than after administration of thyrotropin. CONCLUSIONS Thyrotropin stimulates radioiodine uptake for scanning in patients with thyroid cancer, but the sensitivity of scanning after the administration of thyrotropin is less than that after the withdrawal of thyroid hormone. Thyrotropin scanning is associated with fewer symptoms and dysphoric mood states.

The effects of nonthyroid disease and drugs on thyroid function tests.

Serious nonthyroid illness and caloric deprivation, which so often accompany systemic illness, have diverse and still incompletely understood effects on thyroid hormone economy. We have discussed the pathophysiologic basis for the most common pattern of alterations in routine thyroid function tests: a decreased serum T3 concentration; normal or, in critically ill patients, a low total serum T4 level; and a normal free T4 concentration. Another, less frequent pattern (high total and free T4 with a normal serum T3) can be encountered transiently in the acutely ill medical or psychiatric patient. With the recent advent of sensitive assays for TSH and better methods for serum free T4, it is now possible to define more quickly and accurately the thyroid-metabolic status of most of these sick patients; the vast majority are euthyroid. Certain drugs confound the picture. The most important of these include dopamine and high-dose glucocorticoids, both of which suppress TSH secretion from the pituitary and may actually cause a state of central hypothyroidism. Other drugs have multiple effects on thyroid hormone indices (e.g., amiodarone). Knowledge of all of the ways in which systemic illness, starvation, and certain drugs may influence thyroid function tests is crucial in assessing the thyroid status of patients with serious nonthyroid disease.

Serum thyroxine, free T4, triiodothyronine, and reverse-T3 in diphenylhydantoin-treated patients.

In order to determine the effects of the administration of diphenylhydantoin (DPH) on various parameters of thyroid function, serum samples from 47 male adults receiving therapeutic doses of DPH and 45 euthyroid control subjects were analyzed for total thyroxine (T4) and an index of free T4 concentration, using both a competitive protein-binding assay (CPBA) and a solid-phase radioimmunoassay (RIA), total 3,5,3′-triiodothyronine (T3), 3,3′,5′-triiodothyronine (reverse-T3, rT3), and TSH, each measured by specific RIA. Mean total T4 by both methods was depressed in the DPH group to 0.78 of the control level. Free T4 Index by RIA was decreased on the average in DPH-patients exactly in proportion to the depression in total T4. By the CPBA, the difference between two groups in Free T4 Index was less marked but still significant (DPH/controls = 0.86, p < 0.01). The concentrations of total T3 were virtually identical in the DPH and the control groups. The average T3T4 ratio was significantly higher in the DPH patients than in the controls (0.0178 versus 0.0132, p < 0.001). Serum rT3 was depressed by DPH-treatment in approximately the same proportion to the decrease in total T4. None of the DPH-patients had an elevated serum TSH. The above findings are interpreted as indirect evidence in support of the view that DPH stimulates T4 metabolism, particularly the conversion of T4 to T3. The normal level of free T3 may help to maintain a euthyroid state in spite of the decrease in free T4. The data also define the “euthyroid” ranges for total and free T4 levels by these methods in patients receiving DPH.

Thyroxine transport and distribution in Nagase analbuminemic rats.

The postulate that thyroxine (T4) in plasma enters tissues by protein-mediated transport or enhanced dissociation from plasma-binding proteins leads to the conclusion that almost all T4 uptake by tissues in the rat occurs via the pool of albumin-bound T4 (Pardridge, W. M., B. N. Premachandra, and G. Fierer. 1985. Am. J. Physiol. 248:G545-G550). To directly test this postulate, and to test more generally whether albumin might play a special role in T4 transport in the rat, we performed in vivo kinetics studies in six Nagase analbuminemic rats and in six control rats, all of whom had similar serum T4 concentrations and percent free T4 values. Evaluation of the plasma disappearance curves of simultaneously injected 125I-T4 and 131I-albumin indicated that the flux of T4 from the extracellular compartment into the rapidly exchangeable intracellular compartment was similar in the analbuminemic rats (51 +/- 21 ng/min, mean +/- SD) and in the control rats (54 +/- 15 ng/min), as was the size of the rapidly exchangeable intracellular pool of T4 (1.13 +/- 0.53 vs. 1.22 +/- 0.36 micrograms). This latter finding was confirmed by direct analysis of tissue samples (liver, kidney, and brain). We also performed in vitro kinetics studies using the isolated perfused rat liver. The single-pass fractional extraction by normal rat liver of T4 in pooled analbuminemic rat serum was indistinguishable from that of T4 in pooled control rat serum (10.9 +/- 3.3%, n = 3, vs. 11.4 +/- 3.4%). When greater than 98% of the albumin was removed from normal rat serum by chromatography with Affi-Gel blue, the single-pass fractional extraction of T4 (measured by a bolus injection method) did not change (16.3 +/- 2.1%, n = 5, vs. 15.2 +/- 2.5%). These data provide the first valid experimental test of the enhanced dissociation hypothesis and indicate that there is no special, substantive role for albumin in T4 transport in the rat.

Preparation of 125-I-labeled human thyroxine-binding alpha globulin and its turnover in normal and hypothyroid subjects.

A protein with the electrophoretic, immunologic, and hormone-binding properties of thyroxine-binding globulin (TBG) has been prepared from human plasma and labeled with radioiodine (125-I) by an enzymatic method of iodination. The [125-I]TBG retained the electrophoretic and immunologic characteristics of unlabeled TBG but exhibited a partial loss of thyroxine-binding activity, as assessed by affinity chromatography. The in vivo behavior of [125I]TBG was studied in six euthyroid subjects (controls) with normal serum levels of TBG as measured both by radioimmunoassay and by determination of maximal T4-binding capacity and in four male patients with untreated primary hyperthyroidism, three of whom had elevated serum TBG. The half-time of the final slope of the plasma disappearance curve averaged 5.0 days plus or minus 1.2 (SD) in the controls and ranged from 3.9 to 109 days in the hypothyroid patients. The distribution volume was similar in the two groups, 6.7 plus or minus 1.3 vs. 7.1 plus or minus 2.1 liters. The catabolic clearance rate averaged 0.99 plus or minus 0.33 liters plasma/24 h in the controls and 0.92 plus or minus 0.46 in the hypothyroids. The absolute turnover rate of TBG, calculated from the catabolic clearance rate multiplied by the serum concentration of radioimmunoassayable TBG, averaged 17.8 plus or minus 2.1 mg/day in the controls and ranged from 14.8 to 33.2 mg/day in the hypothyroids. Among the entire group of subjects there was no correlation between the serum TBG concentration and the absolute turnover rate of TBG.

Inability to detect an inhibitor of thyroxine-serum protein binding in sera from patients with nonthyroid illness☆☆☆

Sera from 111 patients hospitalized on acute-care wards (including 32 in the intensive care unit) were examined for the possible presence of inhibitors of thyroxine (T4)-serum protein binding in an assay employing equilibrium dialysis. In 38 of these sera, the unbound (free) T4 fraction was 50% or more higher than the free T4 fraction in a pool of normal sera. From the free T4 fraction in each of the 111 serum samples and the free T4 fraction in the pool of normal sera, the predicted free T4 fractions in mixtures (1:1) of each of these sera with the normal pool were calculated (assuming the absence of binding inhibitors) from the appropriate mass action equations. It was reasoned that a free T4 fraction in any mixture that exceeded this predicted value would indicate the possible presence of a binding inhibitor. (The normal pool was selected for having a low serum triglyceride concentration, to minimize in vitro generation of free fatty acids.) However, for the 111 serum samples studied, the free T4 fraction in the mixture exceeded the upper 95% confidence limit of this predicted value in only one case, and then just barely. Thus, evidence for an inhibitor of T4-serum protein binding in sera from patients with nonthyroid illness could not be found. Twenty-eight of the serum samples were also examined in a similar assay that employed ultrafiltration of undiluted serum instead of equilibrium dialysis. Evidence for an inhibitor of T4-serum protein binding similarly could not be found. Because part of the reason for postulating the existence of such a binding inhibitor has been the performance of the triiodothyronine (T3) resin uptake test in patients with nonthyroid illness, an alternative explanation for this phenomenon was sought. When thyroid hormone-binding globulin (TBG) was desialylated by treatment with neuraminidase, its avidity for T4 was markedly decreased, but its avidity for T3 was unchanged. Thus, if desialylated TBG circulates in patients with nonthyroid illness as previously reported, it could explain not only the low serum T4 concentrations despite near normal immunoreactive TBG concentrations, but also the poor performance of the T3 resin uptake test (where T4 binding capacity is overestimated) in these patients.

Brain lipoprotein lipase is responsive to nutritional and hormonal modulation

Functional lipoprotein lipase activity was recently described in rat brain. The present study was performed to further characterize the biologic significance of brain lipoprotein lipase (heparin releasable component) and elucidate regulatory factors. Comparative studies were performed on tissue (brain, adipose, and heart) heparin releasable lipoprotein lipase in the fasted and diabetic (streptozotocin 100 mg/kg BW IP) rat. Both fasting (96 hours) and diabetes (ten days) significantly decreased brain (cortical) (P less than .05) and adipose (epididymal fat pad) (P less than .001) lipoprotein lipase activity. In contrast, heart muscle enzyme activity was significantly increased (P less than .001) in response to fasting and diabetes. Refeeding (Purina chow 96 hours) and insulin replacement (96 hours) reversed these changes in tissue lipoprotein lipase consequent to fasting and diabetes, respectively. There was a positive correlation between the changes in serum insulin concentration and adipose lipoprotein lipase, but there was no correlation between this parameter and brain or heart lipoprotein lipase. In addition, although T3 therapy normalized the low T3 state associated with both fasting and diabetes, it had no effect on the enzyme activity in the studied tissues. However, subsequent studies demonstrated that hypothyroidism (2 weeks post thyroidectomy) significantly decreased brain lipoprotein lipase activity (P less than .001) and increased both the adipose (P less than .025) and heart (P less than .025) enzyme activity. T3 replacement (0.8 micrograms/100 BW/d for 1 week) reversed the effects of hypothyroidism. However, the relationship between brain enzyme activity and serum T3 was nonlinear as hyperthyroidism tended to reduce brain LPL activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Phenformin in nondiabetic humans. Estimation of glucose turnover rate and Cori Cycle activity

Abstract Glucose turnover and the rate of recycling of glucose carbon into glucose, before and after a two day course of Phenformin 100 mg./day, has been evaluated with the aide of C-6 labeled 14 C glucose in the nondiabetic human subject. These studies providing a measure of true glucose turnover and utilizing each subject as his own control support earlier data on this aspect of the action of Phenformin that had been obtained with uniformly labeled glucose in two groups of nondiabetic subjects. Direct evidence of increased Cori Cycle activity as measured by the appearance of 14 C label in the C-(1–5) moiety of glucose and the evidence that glucose turnover increased by a factor of 2x the increase in the rate of glucose recycling suggest that gluconeogenesis is stimulated when this drug is given to humans. Ancillary measurement of the rate of glucose oxidation before and after Phenformin shows a slight stimulation of this aspect of glucose metabolism in the nondiabetic human following the drug, a finding that is concert with an earlier demonstration of significant increases in glucose oxidation in diabetic subjects treated with Phenformin.

Thyroid Hormone Export in Rat FRTL-5 Thyroid Cells and Mouse NIH-3T3 Cells Is Carrier-Mediated, Verapamil-Sensitive, and Stereospecific1

Export of l-T3 out of the cell is one factor governing the cellular T3 content and response. We previously observed in liver-derived cells that T3 export was inhibited by verapamil, suggesting that it is due to either ATP-binding cassette/multidrug resistance (MDR1/mdr1b) or multidrug resistance-related (MRP1/mrp1) proteins. To test this hypothesis we measured T3 export in FRTL-5, NIH-3T3, and rat hepatoma (HTC) cells that varied in expression of these proteins. FRTL-5 and NIH-3T3 cells were found to contain a T3 efflux mechanism that is verapamil inhibitable, saturable, and stereospecific. By contrast, T3 efflux in HTC cells was slow and unaffected by verapamil. Neither FRTL-5 nor NIH-3T3 cells express mdr1b, but all three cell types express mrp1, as assessed by immunoblotting. Overexpression of MDR1 in NIH-3T3 cells did not enhance verapamil-inhibitable T3 efflux. Photoaffinity labeling of FRTL-5 and NIH-3T3 cells with[ 125I]l-T3 revealed a labeled 90- to 100-kDa protein that was not present in HTC cell...

Early Effects of Thyrotropin on Biosynthesis of Thyroglobulin in the Rat.

Summary The effect of a single dose of TSH on the incorporation in vivo of 14C labeled amino acids into thyroid proteins of the rat have been studied. Soluble thyroid proteins were analyzed by sucrose density-gradient ultracentrifugation. TSH, injected 2 to 4 hours before pulse-labeling, increased the total amount of 14C in protein and accelerated the appearance of label in 19 S thyroglobulin. When TSH was given within one hour of labeling or two hours afterwards, total 14C incorporation was unaffected, but the label appeared in mature (18-19 S) thyroglobulin at the expense of label in an immature (15-16 S) precursor protein. The results suggest that TSH produces an early stimulation of several phases of thyroglobulin biosynthesis.