Download Hyperthyroidism and cation pumps in human skeletal muscle

Am J Physiol Endocrinol Metab 288: E1265–E1269, 2005.
First published December 14, 2004; doi:10.1152/ajpendo.00533.2004.
TRANSLATIONAL PHYSIOLOGY
Hyperthyroidism and cation pumps in human skeletal muscle
Anne Lene Dalkjær Riis,1 Jens Otto Lunde Jørgensen,1
Niels Møller,1,2 Jørgen Weeke,1 and Torben Clausen3
1
Medical Department M (Endocrinology and Diabetes) and 2Medical Research Laboratories,
Aarhus University Hospital, and 3Institute of Physiology, University of Aarhus, Aarhus, Denmark
Submitted 2 November 2004; accepted in final form 6 December 2004
Ca2⫹-activated adenosine triphosphatase; Na⫹-K⫹-activated adenosine triphosphatase; energy expenditure
6 h was fourfold larger than in soleus from euthyroid rats (11).
Thus thyroid hormones markedly upregulate the capacity for
Ca2⫹ uptake, allowing increased recycling of Ca2⫹ and ATP
turnover. The stimulation of energy expenditure (EE) induced
by thyroid hormones is for a significant part mediated by an
increase in the capacity and activity of the Ca2⫹-ATPase in SR
(4, 6, 25). The effects of thyroid hormones on the content and
activity of Na⫹-K⫹-ATPase in skeletal muscle, however, accounts at most for only 15% of their thermogenic action (4).
We have previously demonstrated that the content of Na⫹-K⫹ATPase in human skeletal muscle is closely correlated to plasma
3,5,3⬘-triiodothyronine (T3) and thyroxine (T4) (17), but the relations between thyroid status and the total content of Ca2⫹-ATPase
in human skeletal muscle have not been characterized. In a
controlled design, we examined the effect of hyperthyroidism on
the contents of Ca2⫹-ATPase and Na⫹-K⫹-ATPase in human
skeletal muscle in hyperthyroid patients with Graves’ disease
before and after treatment and compared with healthy control
subjects. We are testing the following hypotheses.
1) In hyperthyroid subjects, the contents of Ca2⫹-ATPase
and Na⫹-K⫹-ATPase in skeletal muscle are increased and
restored toward the normal level following standard treatment
of hyperthyroidism.
2) The contents of Ca2⫹-ATPase and Na⫹-K⫹-ATPase in
skeletal muscle are correlated to REE and plasma thyroid
hormones.
METHODS
of resting energy
expenditure (REE) in humans, and skeletal muscle constitutes
the major target organ for the thermogenic action of thyroid
hormones. Skeletal muscle is by far the most abundant tissue of
the human body and accounts for more than 25% of the total
resting O2 consumption (4, 23, 31). Thus even a modest change
in heat production in skeletal muscles leads to a significant
modification of total body heat production (6). Animal studies
show that thyroid hormones upregulate the content of Ca2⫹ATPase in the sarcoplasmic reticulum (SR) and the maximum
rate of Ca2⫹ uptake in SR from rat soleus increases over a
fourfold range with thyroid status (14, 26). More recently, the
amount of SR protein recovered from hyperthyroid rabbit
muscle was found to be fourfold larger than that obtained from
control animals (6). In intact soleus muscles prepared from
hyperthyroid rats, the accumulation of 45Ca as measured over
Participants. Eleven hyperthyroid patients (9 women and 2 men)
with newly diagnosed Graves’ disease were studied before and after 3
mo of medical treatment with methimazole. The clinical diagnosis of
diffuse toxic goiter was confirmed by measurement of thyroid-stimulating hormone (TSH) receptor antibodies ⬎2 IU/l. In two cases,
muscle biopsies could not be obtained: in one female hyperthyroid
patient (before treatment) and in one female euthyroid patient (after
treatment). These two patients did not differ from the rest of the
patients, and the data from those patients are included in the mean
values and in the unpaired analysis comparing with healthy control
subjects. In the paired comparisons before and after treatment, however, only nine patients could be included. An age-matched control
group of eight healthy women using no medication was studied once.
All participants gave their written informed consent after receiving
oral and written information concerning the study according to the
Declaration of Helsinki II. The Aarhus County Ethical Scientific
Committee approved the study, approval number 1998/4372.
Address for reprint requests and other correspondence: A. L. D. Riis,
Medical Dept. M, Aarhus Univ. Hospital, 8000 Aarhus C, Denmark (E-Mail:
[email protected]).
The costs of publication of this article were defrayed in part by the payment
of page charges. The article must therefore be hereby marked “advertisement”
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
LEAN BODY MASS IS A MAJOR DETERMINANT
http://www.ajpendo.org
0193-1849/05 $8.00 Copyright © 2005 the American Physiological Society
E1265
Downloaded from http://ajpendo.physiology.org/ by 10.220.33.4 on June 15, 2017
Riis, Anne Lene Dalkjær, Jens Otto Lunde Jørgensen, Niels
Møller, Jørgen Weeke, and Torben Clausen. Hyperthyroidism and
cation pumps in human skeletal muscle. Am J Physiol Endocrinol
Metab 288: E1265–E1269, 2005. First published December 14, 2004;
doi:10.1152/ajpendo.00533.2004.—Skeletal muscle constitutes the
major target organ for the thermogenic action of thyroid hormone. We
examined the possible relation between energy expenditure (EE),
thyroid status, and the contents of Ca2⫹-ATPase and Na⫹-K⫹-ATPase
in human skeletal muscle. Eleven hyperthyroid patients with Graves’
disease were studied before and after medical treatment with methimazole and compared with eight healthy subjects. Muscle biopsies were
taken from the vastus lateralis muscle, and EE was determined by
indirect calorimetry. Before treatment, the patients had two- to fivefold elevated total plasma T3 and 41% elevated EE compared with
when euthyroidism had been achieved. In hyperthyroidism, the content of Ca2⫹-ATPase was increased: (mean ⫾ SD) 6,555 ⫾ 604 vs.
5,212 ⫾ 1,580 pmol/g in euthyroidism (P ⫽ 0.04) and 4,523 ⫾ 1,311
pmol/g in healthy controls (P ⫽ 0.0005). The content of Na⫹-K⫹ATPase showed 89% increase in hyperthyroidism: 558 ⫾ 101 vs.
296 ⫾ 34 pmol/g (P ⫽ 0.0001) in euthyroidism and 278 ⫾ 52 pmol/g
in healthy controls (P ⬍ 0.0001). In euthyroidism, the contents of both
cation pumps did not differ from those of healthy controls. The
Ca2⫹-ATPase content was significantly correlated to plasma T3 and
resting EE. This provides the first evidence that, in human skeletal
muscle, the capacity for Ca2⫹ recycling and active Na⫹-K⫹ transport
are correlated to EE and thyroid status.
E1266
CATION PUMPS IN HYPERTHYROIDISM
Table 1. Clinical characteristics and thyroid hormones in 11 hyperthyroid patients before
and after treatment and in 8 control subjects
Patients
Age, yr (range)
BMI, kg/m2
EE, kcal/24 h
Total T3, (1.1–2.6) nmol/l
Total T4, (58–161) nmol/l
Free T3, (3.7–9.5) pmol/l
Free T4 (12–33) pmol/l
TSH, ␮mol/ml median (range)
P Values
Hyperthyroid
Euthyroid
P Values
Ht. vs. Eut.
36⫾9 (26–49)
20.8⫾2.3
2091⫾384
7.7⫾2.5
253⫾49
43⫾18
140⫾51
⬍0.002
22.4⫾2.6
1485⫾239
1.7⫾0.5
94⫾33
7.9⫾3.0
26⫾7
0.0019 (⬍0.002–0.07)
0.0007
⬍0.0001
⬍0.0001
⬍0.0001
0.0004
0.0001
0.068
Control Subjects
Cont. vs. Ht.
Cont. vs. Eut.
40⫾8 (24–46)
24.5⫾4.1
1498⫾163
1.3⫾0.2
77⫾15
6.3⫾0.7
23⫾3
1.5 (0.02–2.58)
0.5
0.03
0.0009
⬍0.0001
⬍0.0001
⬍0.0001
⬍0.0001
⬍0.0001
0.2
0.9
0.02
0.2
0.2
0.3
0.0003
Procedures. REE was evaluated by indirect calorimetry (Deltatrac;
Datex Instrumentarium, Helsinki, Finland). Under local anaesthesia,
needle biopsies were taken from the vastus lateralis muscle with a
Bergström needle and immediately frozen in liquid N2 for later
measurements.
Ca2⫹-activated adenosine triphosphatase (Ca2⫹-ATPase) and Na⫹K⫹-ATPase contents in the muscle biopsies were determined as
described in detail elsewhere (10, 21). For the measurement of
Ca2⫹-ATPase, ⬃30 mg of frozen muscle tissue were homogenized at
0°C in a HEPES-sucrose buffer (pH 7.4) with an Ultra-Turrax homogenizer. To obtain a smaller particle size, the suspension was
further homogenized at 0°C using a glass homogenizer with a tightfitting Teflon pestle rotating at 1,000 rpm. Aliquots (0.2 ml) of the
homogenate were reacted for 30 s at 0°C in 3 ml of a buffer containing
(in mM): 100 imidazole, 100 KCl, 5 MgCl2, 0.5 EGTA, 0.05 ATP.
[␥-32P]ATP (0.3 ␮Ci/ml) was added as a tracer (pH 7.4). In a parallel
assay, CaCl2 (0.55 mM) was added to the medium so as to establish
a free Ca2⫹ content of ⬃50 ␮M. The phosphorylation reaction was
started by addition of the homogenate (0.2 to 2.8 ml of medium) and
30 s later quenched with trichloroacetic acid and centrifuged, the
pellet was resuspended and recentrifuged, and the final pellet was
prepared for counting of 32P bound to the protein. The increase in 32P
uptake induced by the presence of Ca2⫹ was expressed in picomoles
per gram tissue wet weight. Na⫹-K⫹-ATPase was measured as the
[3H]ouabain binding capacity of muscle tissue specimens weighing
⬃5 mg (21). The tissue samples were equilibrated for 2 h at 37°C in
a Tris-vanadate buffer containing [3H]ouabain (10⫺6 M and 0.6
␮Ci/ml) and henceforth washed for 4 ⫻ 30 min in ice-cold Trisvanadate buffer to remove the [3H]ouabain not bound to the tissue,
blotted, weighed, and taken for counting. After correction for unspecific uptake, isotopic purity (95%), loss of 3H activity during the
washout in the cold, and incomplete saturation, the [3H]ouabain
bound was expressed in picomoles per gram tissue wet weight. The
immunoblotting methods generally yield only relative values for
tissue contents of cation ATPases. In the present study, therefore, the
above-mentioned methods were preferred to obtain values that could
be expressed in molar units per gram tissue wet weight. (5). Plasma
thyroid hormones (total T3 and total T4) and TSH were measured by
immunofluorescence methods (Immulite; DPC, Los Angeles, CA).
Free T4 (fT4) and free T3 (fT3) were measured by RIA (28, 29).
Statistical analysis. Statistical analyses were made using SPSS for
Windows 10.0 (SPSS, Chicago, IL). All data (except TSH) are given
as means ⫾ SD. Student’s two-tailed t-test for paired or unpaired data
was used for comparison of data between groups as appropriate. Data
corresponding to serum TSH are given as medians and ranges, and for
comparisons Wilcoxon’s signed rank test or Mann-Whitney U-test
were used. P values ⬍ 0.05 were considered statistically significant.
In the two cases where muscle biopsies could not be obtained both
AJP-Endocrinol Metab • VOL
before and after treatment, the data are included in the mean values
and in the unpaired comparison with healthy control subjects. The
paired comparisons before and after treatment comprise nine patients
as regards Ca2⫹-ATPase and eight patients as regards Na⫹-K⫹ATPase. Pearson’s product moment correlation with two-tailed probability values was used to measure the strength of association between
the variables.
RESULTS
Thyroid status and cation pumps. In the hyperthyroid state,
the patients had between two- and fivefold increased plasma
total T3 and fT3 compared with posttreatment, when T3 decreased to normal levels (Table 1). Upon admission, the patients were clinically hyperthyroid with tachycardia and 41 ⫾
18% increase in REE. Body weight increased 4.7 ⫾ 2.8 kg
during treatment. As shown in Fig. 1, in hyperthyroid patients
the content of Ca2⫹-ATPase in vastus lateralis was increased:
6,555 ⫾ 604 vs. 5,212 ⫾ 1,580 pmol/g after treatment (P ⫽
0.04, paired comparison, n ⫽ 9) and 4,523 ⫾ 1,311 pmol/g in
healthy controls (P ⫽ 0.0005). The mean relative increase in
Ca2⫹-ATPase in hyperthyroidism makes up 26% of the values
measured after euthyroidism had been restored and 45% of the
Ca2⫹-ATPase content in healthy controls. As shown in Fig. 2,
the content of Na⫹-K⫹-ATPase showed a 89% increase in
Fig. 1. Skeletal muscle Ca2⫹-ATPase in 11 hyperthyroid patients before (n ⫽
10) and after treatment (euthyroid, n ⫽ 10) and in 8 healthy controls. Mean
values with bars showing SD. P values represent comparison between patients
in the hyperthyroid and euthyroid states by use of paired t-test (n ⫽ 9) and
comparisons of healthy controls with patients in the hyperthyroid or euthyroid
state by use of unpaired t-test. NS, not significant.
288 • JUNE 2005 •
www.ajpendo.org
Downloaded from http://ajpendo.physiology.org/ by 10.220.33.4 on June 15, 2017
Data are presented as means ⫾ SD, except for thyroid-stimulating hormone (TSH) values, which are presented as medians and range. Normal ranges for thyroid
hormones in our laboratory are stated in parentheses. Ht., hyperthyroid patients before treatment; Eut., hyperthyroid patients after treatment; Cont., controls; BMI,
body mass index; EE, energy expenditure. T3, 3,5,3⬘-triiodothyronine; T4, thyroxine. P values represent comparisons between patients in the hyperthyroid and
euthyroid states by paired t-test and comparisons of healthy controls with patients in the hyperthyroid or euthyroid state by unpaired t-test.
CATION PUMPS IN HYPERTHYROIDISM
E1267
0.54, P ⫽ 0.03 Na⫹, K⫹-ATPase: r ⫽ 0.63, P ⫽ 0.02. Na⫹,
K⫹-ATPase correlations to total T3: r ⫽ 0.92, P ⬍ 0.0001, fT3:
r ⫽ 0.91, P ⬍ 0.0001, fT4: r ⫽ 0.87, P ⬍ 0.0001, total T4: r ⫽
0.84, P ⬍ 0.0001, EE/kg body wt: r ⫽ 0.79, P ⫽ 0.0003.
DISCUSSION
hyperthyroidism: 558 ⫾ 101 vs. 296 ⫾ 34 pmol/g in euthyroidism (P ⫽ 0.0001, paired comparison, n ⫽ 8) and 278 ⫾ 52
pmol/g in healthy controls (P ⬍ 0.0001). After restoration of
euthyroidism, the contents of both cation pumps were not
significantly different from those of healthy controls.
In hyperthyroid patients and healthy controls, Ca2⫹-ATPase
and Na⫹-K⫹-ATPase contents were positively correlated to
circulating free and total thyroid hormone levels and to EE per
kilogram of lean body mass, and the two cation pumps were
intercorrelated (Fig. 3). Ca2⫹-ATPase correlations to total T3:
r ⫽ 0.74, P ⫽ 0.001, fT3: r ⫽ 0.69, P ⫽ 0.006, fT4: r ⫽ 0.61,
P ⫽ 0.022, total T4: r ⫽ 0.68, P ⫽ 0.004, EE/kg body wt: r ⫽
Fig. 3. Correlations in hyperthyroid patients
and healthy controls between total 3,5,3⬘triiodothyronine (T3) and skeletal muscle
Ca2⫹-ATPase and Na⫹-K⫹-ATPase (A) and
between skeletal muscle Ca⫹-ATPase and
Na⫹-K⫹-ATPase and energy expenditure
(EE) per kg body wt (B).
AJP-Endocrinol Metab • VOL
288 • JUNE 2005 •
www.ajpendo.org
Downloaded from http://ajpendo.physiology.org/ by 10.220.33.4 on June 15, 2017
Fig. 2. Skeletal muscle Na⫹-K⫹-ATPase in 9 hyperthyroid patients before and
after treatment (euthyroid, n ⫽ 8) and in 8 healthy controls. Mean values with
bars showing SD. P values represent the comparison between patients in the
hyperthyroid and euthyroid states by use of paired t-test (n ⫽ 8) and comparisons of healthy controls with patients in the hyperthyroid or euthyroid state by
use of unpaired t-test.
Probably the most important new information gained from
the present study is that in hyperthyroidism the content of
Ca2⫹-ATPase in human skeletal muscle is increased. Moreover, this increase is normalized by achievement of euthyroidism by standard methimazole treatment and shows significant
correlation to plasma thyroid hormone levels as well as to
energy expenditure. Our values for the contents of Ca2⫹ATPase and Na⫹-K⫹-ATPase in skeletal muscle of healthy
control subjects correspond closely to those previously published by our laboratory and others (5, 10).
In all our patients, we confirm our previous finding of
elevated Na⫹-K⫹-ATPase content in human skeletal muscle in
hyperthyroidism and its normalization after treatment (17).
Hyperthyroid patients suffer from muscle weakness, fatigue,
and decreased contractility, which are normalized after treatment (22). The gross increase in skeletal muscle Na⫹-K⫹ATPase in hyperthyroidism is thus unlike the upregulation
induced by physical training, not associated with increased
muscle strength. This is probably due to a concomitant increase
in the content of Na⫹ channels in muscle, as demonstrated in
animal studies (15), allowing increased passive flux of Na⫹
into the muscle cells dissipating the membrane potential and
reducing excitability and contractility (5). In the rat, the increase in the content of Na⫹ channels and passive Na⫹-K⫹
fluxes induced by thyroid hormone treatment precedes the
E1268
CATION PUMPS IN HYPERTHYROIDISM
AJP-Endocrinol Metab • VOL
panied by normalization of REE. The increased content of
Ca2⫹-ATPase in skeletal muscle can only in part explain the
increase in REE in hyperthyroidism. Thyroid hormone affects energy balance by several mechanisms (24). In hyperthyroidism, spontaneous physical activity is increased (19).
Thyroid hormone regulates gene expression of a large number of proteins known to regulate energy expenditure, for
example uncoupling protein-3 (18), and increased protein
synthesis also consumes energy (2).
In summary, our data are consistent with the hypothesis
that, in human subjects, the calorigenic actions of thyroid
hormones are in part mediated by increased skeletal muscle
content of Ca2⫹-ATPase, allowing for increased energy
expenditure by both active Ca2⫹ transport and uncoupled
ATPase activity. We confirm our previous finding of elevated Na⫹-K⫹-ATPase content in skeletal muscle in hyperthyroidism, which to a minor extent adds to the increased
energy expenditure by increased active Na⫹-K⫹ transport.
In a wider perspective, active Ca2⫹ transport in skeletal
muscle may be a regulatory target for energy turnover and
weight control.
ACKNOWLEDGMENTS
Tove Lindahl Andersen is thanked for excellent technical assistance.
GRANTS
The study was supported by Aarhus Universitets Forskningsfond and the
Danish Biomembrane Research Center. Parts of the results were presented at
the 85th Annual Scientific Meeting of the Endocrine Society 2003 in Philadelphia, PA.
REFERENCES
1. Arai M, Otsu K, MacLennan DH, Alpert NR, and Periasamy M.
Effect of thyroid hormone on the expression of mRNA encoding sarcoplasmic reticulum proteins. Circ Res 69: 266 –276, 1991.
2. Arruda AP, Da Silva WS, Carvalho DP, and de Meis L. Hyperthyroidism increases the uncoupled ATPase activity and heat production by the
sarcoplasmic reticulum Ca2⫹-ATPase. Biochem J 375: 753–760, 2003.
3. Berchtold MW, Brinkmeier H, and Muntener M. Calcium ion in
skeletal muscle: its crucial role for muscle function, plasticity, and disease.
Physiol Rev 80: 1215–1265, 2000.
4. Clausen T, van Hardeveld C, and Everts ME. Significance of cation
transport in control of energy metabolism and thermogenesis. Physiol Rev
71: 733–774, 1991.
5. Clausen T. Na⫹-K⫹ pump regulation and skeletal muscle contractility.
Physiol Rev 83: 1269 –1324, 2003.
6. De Meis L, Arruda AP, Da-Silva WS, Reis M, and Carvalho DP. The
thermogenic function of the sarcoplasmic reticulum Ca2⫹-ATPase of
normal and hyperthyroid rabbit. Ann NY Acad Sci 986: 481– 488, 2003.
7. De Meis L. Uncoupled ATPase activity and heat production by the
sarcoplasmic reticulum Ca2⫹-ATPase. Regulation by ADP. J Biol Chem
276: 25078 –25087, 2001.
8. Dode L, Andersen JP, Leslie N, Dhitavat J, Vilsen B, and Hovnanian
A. Dissection of the functional differences between sarco(endo)plasmic
reticulum Ca2⫹-ATPase (SERCA) 1 and 2 isoforms and characterization
of Darier disease (SERCA2) mutants by steady-state and transient kinetic
analyses. J Biol Chem 278: 47877– 47889, 2003.
9. Everts ME. Effects of thyroid hormones on contractility and cation
transport in skeletal muscle. Acta Physiol Scand 156: 325–333, 1996.
10. Everts ME, Andersen JP, Clausen T, and Hansen O. Quantitative
determination of Ca2⫹-dependent Mg2⫹-ATPase from sarcoplasmic reticulum in muscle biopsies. Biochem J 260: 443– 448, 1989.
11. Everts ME and Clausen T. Effects of thyroid hormones on calcium
contents and 45Ca exchange in rat skeletal muscle. Am J Physiol Endocrinol Metab 251: E258 –E265, 1986.
12. Everts ME and Clausen T. Effects of thyroid hormone on Na⫹-K⫹
transport in resting and stimulated rat skeletal muscle. Am J Physiol
Endocrinol Metab 255: E604 –E612, 1988.
288 • JUNE 2005 •
www.ajpendo.org
Downloaded from http://ajpendo.physiology.org/ by 10.220.33.4 on June 15, 2017
upregulation of Na⫹-K⫹-ATPase, indicating that the latter is a
compensatory mechanism to maintain transmembrane Na⫹-K⫹
distribution and cell membrane potential (12, 15).
The SR is a specialized Ca2⫹ storage membrane system in
muscle cells and plays a central role in the contractile function
of the muscle by virtue of its ability to regulate cytosolic Ca2⫹
concentration (3, 20). Ca2⫹ release from the SR initiates
muscle contraction, whereas Ca2⫹ reuptake into the SR membrane vesicles lowers cytosolic Ca2⫹, causing muscle relaxation. The events that regulate Ca2⫹ release and removal can
affect cytosolic Ca2⫹ levels and, hence, the rate and extent of
muscle contraction and relaxation. The Ca2⫹ reuptake function
of the SR is mediated by the Ca2⫹ transport pump, the
sarco(endo)plasmic reticulum Ca2⫹-ATPase (SERCA). Ca2⫹
release from the SR to trigger muscle contraction is mediated
by Ca2⫹ channels, the ryanodine receptors. In animals, thyroid
hormones increase the mRNA expression and protein of both
the Ca2⫹-ATPase and the ryanodine receptor in skeletal muscle
(1, 16). This dual upregulation explains that, in rat muscle, both
contraction rates and relaxation rates are increased in hyperthyroidism and decreased in hypothyroidism (9, 13). In keeping with this, one of the classical clinical features of thyroid
disorders is the shortening of the Achilles tendon reflex time in
hyperthyroidism and its prolongation in hypothyroidism (30).
The slow-to-fast transition in hyperthyroid red muscle is
mainly due to increased SERCA1 isoform expression. SERCA1
seems to be the only SERCA isoform able to interconvert
energy from ATP hydrolysis into heat without calcium transport, the uncoupled ATPase activity (7). Recently, an animal
model described how the calorigenic action of thyroid hormone
in hyperthyroidism might be due, at least in part, to the
increased uncoupled ATPase activity in both red and white
muscles (2).
The observed increase in skeletal muscle Ca2⫹-ATPase in
our study might in part be the result of a transition of muscle
fiber types induced by hyperthyroidism from the type I muscle
fibers with a low content of SR and Ca2⫹-ATPase to the type
II muscle fibers with a high content of SR and Ca2⫹-ATPase
(27). Moreover, because SERCA1 has a higher ATP turnover
number (1,000 –1,100/min) than that of SERCA2 (450/min)
(8), an increase in the ratio between type II and type I fibers
further augments the capacity for Ca2⫹ recycling and the ATP
turnover associated with this transport process. Therefore, the
45% increase in Ca2⫹-ATPase content demonstrated in the
present study may be combined with an increased average ATP
turnover number. This would allow for an even more pronounced relative rise in energy expenditure.
We chose to reexamine the patients after 3 mo of treatment,
and at that time the patients were clinically euthyroid, and
circulating thyroid hormones and REE were normalized. We
might have obtained a more complete normalization of the
cation pumps after a longer period of euthyroidism, allowing
for further regeneration of the muscles (22).
Observations of correlations do not establish causality.
The hypothesis that the calorigenic actions of thyroid hormones are in part mediated by increased Ca2⫹ recycling in
the SR of skeletal muscle is generated from knowledge
obtained from animal studies. The human data we present
here cannot disprove this hypothesis; on the contrary, the
hypothesis is supported. Moreover, the downregulation of
Ca2⫹-ATPase induced by the standard therapy was accom-
CATION PUMPS IN HYPERTHYROIDISM
AJP-Endocrinol Metab • VOL
23. Rolfe DF and Brown GC. Cellular energy utilization and molecular
origin of standard metabolic rate in mammals. Physiol Rev 77: 731–758,
1997.
24. Silva JE. The thermogenic effect of thyroid hormone and its clinical
implications. Ann Intern Med 139: 205–213, 2003.
25. Simonides WS, Thelen MH, van der Linden CG, Muller A, and van
Hardeveld C. Mechanism of thyroid-hormone regulated expression of the
SERCA genes in skeletal muscle: implications for thermogenesis. Biosci
Rep 21: 139 –154, 2001.
26. Simonides WS and van Hardeveld C. Effects of the thyroid status on the
sarcoplasmic reticulum in slow skeletal muscle of the rat. Cell Calcium 7:
147–160, 1986.
27. Van der Linden CG, Simonides WS, Muller A, van der Laarse WJ,
Vermeulen JL, Zuidwijk MJ, Moorman AF, and van Hardeveld C.
Fiber-specific regulation of Ca2⫹-ATPase isoform expression by thyroid
hormone in rat skeletal muscle. Am J Physiol Cell Physiol 271: C1908 –
C1919, 1996.
28. Weeke J, Boye N, and Ørskov H. Ultrafiltration method for direct
radioimmunoassay measurement of free thyroxine and free tri-iodothyronine in serum. Scand J Clin Lab Invest 46: 381–389, 1986.
29. Weeke J and Ørskov H. Ultrasensitive radioimmunoassay for direct
determination of free triiodothyronine concentration in serum. Scand
J Clin Lab Invest 35: 237–244, 1975.
30. Wiles CM, Young A, Jones DA, and Edwards RH. Muscle relaxation
rate, fibre-type composition and energy turnover in hyper- and hypothyroid patients. Clin Sci (Lond) 57: 375–384, 1979.
31. Zurlo F, Larson K, Bogardus C, and Ravussin E. Skeletal muscle
metabolism is a major determinant of resting energy expenditure. J Clin
Invest 86: 1423–1427, 1990.
288 • JUNE 2005 •
www.ajpendo.org
Downloaded from http://ajpendo.physiology.org/ by 10.220.33.4 on June 15, 2017
13. Everts ME, van Hardeveld C, Ter Keurs HE, and Kassenaar AA.
Force development and metabolism in perfused skeletal muscle of euthyroid and hyperthyroid rats. Horm Metab Res 15: 388 –393, 1983.
14. Fitts RH, Winder WW, Brooke MH, Kaiser KK, and Holloszy JO.
Contractile, biochemical, and histochemical properties of thyrotoxic rat
soleus muscle. Am J Physiol Cell Physiol 238: C14 –C20, 1980.
15. Harrison AP and Clausen T. Thyroid hormone-induced upregulation of
Na⫹ channels and Na⫹-K⫹ pumps: implications for contractility. Am J
Physiol Regul Integr Comp Physiol 274: R864 –R867, 1998.
16. Jiang M, Xu A, Tokmakejian S, and Narayanan N. Thyroid hormoneinduced overexpression of functional ryanodine receptors in the rabbit
heart. Am J Physiol Heart Circ Physiol 278: H1429 –H1438, 2000.
17. Kjeldsen K, Nørgaard A, Gøtzsche CO, Thomassen A, and Clausen T.
Effect of thyroid function on number of Na-K pumps in human skeletal
muscle. Lancet 2: 8 –10, 1984.
18. Lanni A, Moreno M, Lombardi A, and Goglia F. Thyroid hormone and
uncoupling proteins. FEBS Lett 543: 5–10, 2003.
19. Levine JA, Nygren J, Short KR, and Nair KS. Effect of hyperthyroidism on spontaneous physical activity and energy expenditure in rats.
J Appl Physiol 94: 165–170, 2003.
20. Loukianov E, Ji Y, Baker DL, Reed T, Babu J, Loukianova T, Greene
A, Shull G, and Periasamy M. Sarco(endo)plasmic reticulum
Ca2⫹ATPase isoforms and their role in muscle physiology and pathology.
Ann NY Acad Sci 853: 251–259, 1998.
21. Nørgaard A, Kjeldsen K, and Clausen T. A method for the determination of the total number of 3H-ouabain binding sites in biopsies of human
skeletal muscle. Scand J Clin Lab Invest 44: 509 –518, 1984.
22. Nørrelund H, Hove KY, Brems-Dalgaard E, Jurik AG, Nielsen LP,
Nielsen S, Jørgensen JO, Weeke J, and Møller N. Muscle mass and
function in thyrotoxic patients before and during medical treatment. Clin
Endocrinol (Oxf) 51: 693– 699, 1999.
E1269