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R R Cavalieri

Publications and source records attributed to R R Cavalieri.

At least 19 recordsLinked to original sources
PubMed1992

Deiodination and deconjugation of the glucuronide conjugates of the thyroid hormones by rat liver and brain microsomes.

Radioiodinated thyroxine (T4) glucuronide (T4G) and triiodothyronine (T3) glucuronide (T3G), paired with T4 or T3, were incubated at 37 degrees C for 2 hours in the presence of dithiothreitol and microsomes that had been prepared from euthyroid rat liver or hypothyroid rat brain tissues, as sources of type I and type II iodothyronine 5'-deiodinases, respectively. Incubations with boiled microsomes served as controls. The incubated supernatant was analyzed by high-pressure liquid chromatography (HPLC) for content of T4, T4G, T3, T3G, and combined T2 and T2G. The deiodination of T4G resulted from incubation with both liver and brain microsomes, but was somewhat less active than the deiodination of simultaneously incubated T4. All batches of microsomes studied also caused deconjugation of both T4G and T3G. The data are compatible with the hypothesis that T4G can serve as an alternate pathway for conversion of T4 to T3 in these tissues.

Animals↗
PubMed1992

Hepatic uptake of 3,5,3'-triiodothyronine: electrochemical driving forces.

We used the multiple indicator dilution technique to assess the electrochemical forces driving uptake of 3,5,3'-triiodo-L-thyronine (T3) across the basolateral plasma membrane in the single-pass perfused rat liver. With the use of 4 g/dl albumin solutions, the influx and efflux clearances were 0.020 +/- 0.005 and 0.0049 +/- 0.0017 (SE) ml.s-1.g liver-1, respectively, indicating that the total T3 concentration at equilibrium should be about four times greater in cytoplasm than in plasma. However, when the influx and efflux clearances were divided by the unbound (free) T3 concentration in the perfusate and cytosol, they were not different (3.76 +/- 0.26 vs. 4.30 +/- 0.38 ml.s-1.g liver-1), indicating that the uptake process does not generate a gradient of unbound T3 across the plasma membrane. To further test whether T3 uptake is driven by the electrical potential difference across the plasma membrane, liver cells were depolarized by isosmotic replacement of perfusate chloride with gluconate. There was no effect on uptake or efflux. To test whether uptake is coupled to influx of sodium, perfusate sodium was replaced with choline. Although there was a modest decline in both the influx and efflux clearances, there was no change in their ratio, as would be expected for sodium-coupled active transport. These results indicate that uptake of T3 across the basolateral hepatocyte membrane occurs by passive diffusion. We found no evidence to support concentrative, active transport by either electrogenic or sodium-coupled mechanisms.

Animals↗
PubMed1992

Thyroxine (T4) transport and distribution in rats treated with EMD 21388, a synthetic flavonoid that displaces T4 from transthyretin.

To test whether plasma transthyretin (TTR) might play a specific direct role in the transfer of T4 from the plasma to tissues, in vivo kinetic studies were performed in control rats and in rats treated with EMD 21388, a synthetic flavonoid that displaces T4 from TTR. The plasma disappearance curves of simultaneously injected [125I]T4 and [131I]albumin were analyzed to determine the rate constant for the transfer of T4 from the extracellular compartment to the rapidly exchangeable intracellular compartment (KE) and the steady state distribution ratio of T4 between the rapidly exchangeable intracellular compartment and the extracellular compartment (Imax/Emin). When rats were injected ip with EMD 21388 (2 mumol/100 g BW), the free T4 fraction in serum increased approximately 8-fold. This was due to displacement of T4 from TTR, as assessed by electrophoresis of serum proteins in the presence of [125I]T4. Concomitantly, both KE and Imax/Emin increased 6-fold in the treated rats. These results fail to confirm a major specific role for TTR in the transfer of T4 from the plasma to tissues. Instead, they are consistent with both the free hormone transport hypothesis and the free hormone hypothesis in this setting.

Animals↗
PubMed1991

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.

Blood Proteins↗
PubMed1991

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.

Diabetes Mellitus↗
PubMed1990

Cyclic adenosine 3',5'-monophosphate and glucose stimulate thyroxine 5'-deiodinase type II in cultured mouse neuroblastoma cells.

Nutrient modulation increases mouse neuroblastoma (NB) T4-5'-deiodinase II (T4-5'-D II) activity. Carbohydrates are more potent than either amino acids or glycerol as nutrient sources. Glucose rapidly (2 to 4 hours) enhances NB enzyme activity and the response is dependent on new protein synthesis. The present study was performed to further characterize this glucose effect and explore its relationship to the cyclic adenosine monophosphate (cAMP) system in these cells. NB T4-5'-D II activity reached a maximum level (sixfold) in response to glucose (10 mmol/L) at 16 hours and thereafter remained constant up to 22 hours before reverting back to basal level between 24 and 30 hours. This pattern of response allowed the performance of detailed studies on maximum glucose activated NB T4-5'-D II under transient equilibrium conditions during the 16- to 22-hour period. Addition of dibutyryl cAMP (dbcAMP) (1 mmol/L) at this stage significantly increased enzyme activity (twofold at 2 hours and fourfold at 4 and 6 hours) compared with glucose alone. There was an additive response to dbcAMP under these maximum glucose-activated conditions. Nonactivated NB T4-5'-D II showed a twofold response to dbcAMP (1 mmol/L) at 4 hours in a glucose-free medium. Under these conditions, glucose (10 mmol/L) also increased enzyme activity twofold. Combined studies with dbcAMP and glucose increased enzyme activity fourfold at 4 hours. Subsequent studies were performed with forskolin (10 mumol/L) and cholera toxin (1 nmol/L), modulators of endogenous cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Iodide-induced hypothyroidism in patients after thyroid resection.

The purpose of this investigation was to determine whether an intrinsic defect in thyroid hormone production is required for the development of iodide-induced hypothyroidism or does it also develop in TSH-stimulated normal thyroid tissue. To answer this question, we studied the response to iodine administration (180 mg iodide daily for 3-4 months) in eight euthyroid patients who had had partial thyroidectomies 2 months to 10 years previously for benign thyroid nodules, and in three euthyroid control subjects. In all 11 euthyroid patients, basal serum TSH concentrations increased during iodide administration. In six of the eight patients who had previous thyroid operations and in two of the three control patients, basal serum TSH concentrations increased into the abnormal range (greater than 6 U ml-1). Increased serum TSH concentrations were noted as early as 1 week after potassium iodide had been started and the increased levels persisted during the period of iodide administration. Although basal values for serum TSH concentration were initially within the normal range, those patients with highest basal serum TSH values developed the greatest increase in TSH in response to potassium iodine. Among the eight patients treated by partial thyroidectomy, serum T4 concentrations decreased in five, serum T3 concentration decreased in three and all five developed mild symptoms of hypothyroidism while receiving iodide. Serum T4 concentrations also decreased slightly in two of the three control patients. Serum total iodine levels increased from 7.0 +/- 0.5 to 315.7 +/- 108.6 g dl-1 (mean-+/- standard error) during potassium iodide administration, but there was no correlation between the level of serum iodide concentration achieved and inhibition of thyroid function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

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.

Animals↗
PubMed1989

Uptake of cortisol by the perfused rat liver: validity of the free hormone hypothesis applied to cortisol.

The mechanism by which cortisol in plasma enters hepatic cells was investigated using the isolated perfused rat liver. To determine whether hepatic uptake of cortisol from serum can be accounted for entirely by the pool of unbound (free) cortisol, we compared observed uptake rates with the equilibrium-free fraction of cortisol in serum and the rates of dissociation of cortisol from its serum binding proteins (determined using a rapid filtration assay based on transfer of [3H] cortisol to dextran-coated charcoal). More than 95% of the cortisol in both human and rat serum dissociated spontaneously from its binding proteins within 5 sec at 37 C. The fractional unidirectional hepatic uptakes of cortisol from pooled human serum and pooled rat serum were 59.4 +/- 5.4% and 59.5 +/- 1.0% (mean +/- SE), respectively, at the physiological flow rate of 1 ml/min.g liver. The corresponding free cortisol fractions in these sera were 4.53 +/- 0.15% and 8.16 +/- 0.23%, respectively. The fractional unidirectional hepatic uptake of cortisol from protein-free buffer averaged 99.9% (n = 5) at a flow rate of 3 ml/min.g liver. By calculating the appropriate rate constants and applying the Kety-Renkin-Crone equation to the above data, it can be shown that all of the cortisol taken up from serum by the perfused rat liver can be accounted for by the pool of free cortisol, which turns over very rapidly. The physiological significance of this finding is discussed in terms of a general mathematical model of hormone transport that delineates the conditions under which the free hormone hypothesis is and is not valid.

Animals↗
PubMed1989

Carbohydrate reactivation of thyroxine 5'-deiodinase (type II) in cultured mouse neuroblastoma cells is dependent upon new protein synthesis.

The T3 concentration in brain predominantly reflects local production from T4 rather than T3 uptake from the circulating pool. We recently demonstrated that rat brain T3 content is increased by glucose feeding compared to chow feeding. One possible mechanism for this effect is an increase in brain T4 5'-deiodinase (5'-D) activity. Our recent preliminary studies of neuroblastoma (NB) cells demonstrate that renewal of RPMI-1640 medium stimulates T4 5'-D type II (NB T4 5'-D II) activity in these cells. The present studies were performed to determine the mechanism of this response. Studies were performed on NB cells supported in thyroid hormone-depleted (deficient) medium. This approach increased NB T4 5'-DII activity 4-fold compared to that in thyroid hormone-replete medium. Medium renewal further stimulated enzyme activity (7- to 9-fold; maximum at 6 h) in each group. The difference between the hypothyroid group and control was sustained over a 24-h period. Subsequent studies demonstrated that glucose (11 mM) was the specific medium ingredient mediating the medium renewal response. A progressive increase in NB T4 5'-DII activity was noted over 8 h during RPMI-1640 salt plus glucose (11 mM) incubation. This was equivalent to the effect of complete medium containing glucose (11 mM). Coincubation with insulin (10(-7)-10(-9) M) did not modify the enzyme response to glucose. In addition, fructose (10 mM) had a similar effect on enzyme activity. Glycerol and essential and nonessential amino acids also modestly increased NB T4 5'-DII activity compared to that in the control group (P less than 0.01). Actinomycin-D (1 microM), cycloheximide (100 microM), and puromycin (100 microM) significantly (P less than 0.001) decreased the glucose effect on T4 5'-DII by 5-, 9-, and 17-fold, respectively, after 6 h of incubation. In addition, puromycin (10-200 microM) inhibited both NB T4 5'-DII activity and [3H]amino acid incorporation during incubation in glucose. There was a significant correlation between these parameters (r = 0.8; P less than 0.001). The enzyme activity decay curves in the glucose-activated and control groups subsequent to puromycin (100 microM) addition at 8 h were parallel. The fractional turnover rate was 13%/h in the controls and 11%/h in the glucose groups. The calculated enzyme production rate was significantly higher (P less than 0.005) in the glucose group compared to that in the control group (17.4 vs. 6.8 fmol/mg protein.h).(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1988

Uptake of thyroxine by the perfused rat liver: implications for the free hormone hypothesis.

To investigate the mechanism by which thyroxine (T4) in plasma enters hepatic cells, we measured the rate constants for uptake of free T4 by the perfused rat liver and for dissociation of T4 from its plasma binding proteins. Quantitative autoradiography of liver lobules after perfusion with [125I]T4 indicated an apparent rat constant for removal of free T4 from the sinusoids of at least 1.1 +/- 0.2 s-1. Single-pass extraction of T4 from human serum was 10.6 +/- 1.7% at physiological flow rates (1 ml.min-1.g liver-1). Rate constants for dissociation of T4 from plasma binding proteins at 37 degrees C (determined by rapid filtration) were 0.017 +/- 0.002 s-1 for human thyroid hormone-binding globulin, 0.080 +/- 0.015 s-1 for human thyroid hormone-binding prealbumin, and greater than 0.5 s-1 for human albumin. To investigate the factors that determine the concentration of T4 within hepatic cells, we analyzed the above data together with data reported in the literature on the equilibrium-binding constants and the rate constant for cellular metabolism of T4. Analysis of all of these data using a previously published mathematical model leads to the following conclusions for the physiological state: 1) metabolism, not uptake, is rate limiting to removal of T4 from plasma by the liver; 2) binding equilibrium is present in the intrahepatic plasma; 3) intracellular T4 is in equilibrium with the free T4 pool in plasma (and maintenance of this equilibrium may be an important function of plasma thyroid hormone-binding proteins); and 4) the concentration of T4 within the liver is proportional to the concentration of free T4 in the plasma. Our data do not allow us to determine definitively whether hepatic uptake of T4 occurs only from the free T4 pool in plasma or also from the protein-bound pool by interaction of one or more of the binding proteins with the liver cell. However, mathematical analysis indicates that this distinction is irrelevant to steady-state intracellular hormone concentrations when equilibrium exists between the plasma and cytosolic pools of hormone.

Animals↗
PubMed1988

Carbohydrate feeding increases total body and specific tissue 3,5,3'-triiodothyronine neogenesis in the rat.

The glucose-fed rat, in contrast to the chow-fed animal, has a higher serum total T3 concentration and an increase in the hepatic content of T4 5'-deiodinase (type I) activity. The mechanism and significance of these glucose-induced changes in T3 metabolism are elucidated in this study. To focus on extrathyroidal thyroid hormone metabolism the kinetic parameters were determined in thyroidectomized T4-replaced rats (1.25 micrograms T4/100 g BW.day). Kinetics of T4 and T3 were studied separately by infusing labeled hormone to equilibrium. Glucose feeding for 72 h (G) significantly increased both the total and free serum T3 concentrations compared to the respective means in the chow-fed control group (P). The glucose-induced changes in serum T3 reflect the approximate doubling of T3 production to 14.7 +/- 0.6 ng/h.100 g in G rats compared to 7.6 +/- 0.7 ng/h.100 g in P rats. The higher T3 production rate in the G group is due to a significant increase in the fractional total body T4 to T3 conversion (0.33 +/- 0.02) compared to that in the P group (0.19 +/- 0.02). The tissue (liver, kidney, brain, and brown adipose tissue) concentration of T4 (nanograms per g wet wt) was significantly increased in the G group. The increase ranged from 54% in liver to 80% in kidney, brain, and brown adipose tissue. The tissue concentration of T3 (nanograms per g wet wt) was even more dramatically increased by glucose feeding than was T4. The glucose-induced increment in organ T3 ranged from 2.5-fold (kidney, muscle, and brain) to 5-fold (liver and white adipose tissue) to 12-fold (brown adipose tissue). These data indicate that the increase in serum total and free T3 concentrations associated with glucose feeding reflects augmented total body T3 production from T4. The effect of the enhanced T3 neogenesis was generalized, as the T3 content was increased in each organ studied. Thus, glucose feeding has unique effects on T3 metabolism.

Adipose Tissue↗
PubMed1988

Uptake of 3,5,3'-triiodothyronine by the perfused rat liver: return to the free hormone hypothesis.

To investigate the mechanism by which T3 in plasma enters hepatic cells, we measured rate constants for the uptake of unbound (free) T3 by the perfused rat liver, for the hepatic uptake of T3 from serum, and for the spontaneous dissociation of T3 from its plasma binding proteins. Quantitative autoradiography of liver lobules after perfusion with [125I]T3 in protein-free buffer indicated a high apparent rate constant for removal of T3 from the sinusoids; its minimum estimate was 2.4 +/- 0.2 sec-1. The single pass extraction of T3 in human serum by the perfused rat liver was 31.6 +/- 4.5% at the supraphysiological flow rate of 3 ml/min/g liver (sinusoidal transit time, approximately 3 sec). Sixty percent of the T3 in this serum dissociated spontaneously from its binding proteins in 3 sec, as determined by a rapid filtration assay. Based on these data, we conclude that the pool of free T3 in plasma turns over very rapidly in vivo and probably accounts for the entire hepatic uptake of T3 from plasma. Using additional data on the rate constant for cellular metabolism of T3 obtained from values reported in the literature, a previously published general mathematical model of ligand transport was applied to all of these data, yielding the following conclusions for the physiological state. 1) Metabolism, not uptake, is rate limiting to removal of T3 from plasma by the liver. 2) Intracellular T3 is in virtual equilibrium with the free T3 pool in plasma. 3) Intracellular T3 concentrations reflect the concentration of free T3 in plasma, as predicted by the free hormone hypothesis. It is shown mathematically that these conclusions are independent of whether a gradient exists between extra- and intracellular T3 concentrations, and that they would still hold even if the tissue uptake of T3 occurred by a mechanism that acted directly on the plasma protein-bound pool of T3.

Animals↗
PubMed1988

The acute effects of human growth hormone administration on thyroid function in normal men.

GH replacement therapy may lead to alterations in serum TSH and/or thyroid hormone values in GH-deficient patients, but there is no consensus on the explanation for these changes. We examined the effect of GH administration (0.125 mg, sc, daily for 4 days) on thyroid function in 20 normal men. Serum T4 levels decreased by 8%, and serum free T4 index values decreased by 5%. In contrast, serum T3 levels increased by 21%; serum rT3 did not change. These changes were accompanied by a 54% decrease in the mean serum TSH level. While it is not possible to draw conclusions about hormone production and disposal rates from changes in serum levels, these data are most consistent with enhanced extrathyroidal (including intrapituitary) conversion of T4 to T3 and a compensatory decrease in TSH secretion.

Adult↗
PubMed1988

Reverse T3 and modulators of the calcium messenger system rapidly decrease T4-5'-deiodinase II activity in cultured mouse neuroblastoma cells.

Neural T3 neogenesis is modulated by the enzyme T4-5'-deiodinase type II (T4-5'-DII). Hypothyroidism increases the activity of rat pituitary and cerebral cortex enzyme activity. Mouse neuroblastoma cells (NB41A3) incubated in thyroid hormone deficient medium also show a significant increase in T4-5'-DII activity. This response is rapidly (less than 30 minutes) reversed by reverse T3 (rT3) suggesting a mechanism independent of nuclear T3 receptor binding or new protein synthesis. This report details a series of studies performed to elucidate the nature of this rT3 effect. Confluent neuroblastoma cell culture preparations maintained in hypothyroid medium showed a 2-3 fold increase in T4-5'-DII activity compared to preparations in standard medium (p less than 0.001). RT3 (1-50 nM), the calcium ionophore A23187 (0.3-1.5 microM) and the phorbol ester TPA (0.1-1.0 microM) reversed the effect of thyroid hormone deficient medium on enzyme activity (p less than 0.001). Each agent showed a similar time course with maximal effect occurring between 15-30 minutes post medium supplementation. The suppressive effect of A23187 (1.5 microM) and TPA (0.5 microM) on enzyme activity was not additive. In addition, the combination o of rT3 (50 nM) and A23187 (1.5 nM) did not decrease enzyme activity compared to each agent alone. In contrast, the combined addition of rT3 (50 nM) and TPA (0.5 microM) did have an additive effect on neuroblastoma T4-5'-DII activity. A similar pattern of response was found, when the effects of these agents were analyzed on T4-5'-DII activity in neuroblastoma cells incubated in N-FSC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗