Background: Neuromuscular symptoms and impaired muscle energy metabolism have been described in subclinical hypothyroidism (sHT). Aim: The aim of the study was to evaluate the energy and substrate response to exercise in sHT patients using a standardized protocol and to test the effect of L-T(4) replacement in a double-blind, randomized, placebo-controlled fashion. Patients and Methods: We studied 23 sHT patients and 10 matched euthyroid controls. Oxygen uptake (VO(2)), carbon dioxide output, and heart rate were measured during incremental step-up exercise. Blood glucose, lactate, pyruvate, free fatty acid, glycerol, and beta-hydroxybutyrate concentrations were measured at rest, every 2 min during exercise, and during 20 min of recovery. The exercise protocol was repeated after 6 months of placebo or L-T(4)-restored euthyroidism. Results: Maximal power output ( P = 0.02) and VO(2) max ( P = 0.04) were reduced in sHT, and, with increasing workload, patients achieved higher heart rates ( P < 0.03) at VO(2) values equivalent to those of controls. The respiratory quotient increments were significantly higher in patients than controls ( P < 0.04). Blood lactate and pyruvate and their ratio rose with a steeper slope ( P < 0.0001, P < 0.001, and P < 0.01, respectively) in patients than controls. Resting plasma free fatty acid and blood glycerol levels were significantly higher in patients than controls ( P < 0.0003 and P < 0.003, respectively) throughout baseline, exercise, and recovery. L-T(4) replacement, while improving neuromuscular symptoms, did not produce significant changes in the energy or substrate response to exercise. Conclusions: The response to exercise is altered both in terms of tolerance and pattern of substrate utilization in sHT patients. Restoring stable euthyroidism does not correct this defect over a 1-yr period.
Muscle metabolism and exercise tolerance in subclinical hypothyroidism: A controlled trial of levothyroxine
NATALI, ANDREA;BALDI, SIMONA;DARDANO, ANGELA;MONZANI, FABIO;FERRANNINI, ELEUTERIO
2005-01-01
Abstract
Background: Neuromuscular symptoms and impaired muscle energy metabolism have been described in subclinical hypothyroidism (sHT). Aim: The aim of the study was to evaluate the energy and substrate response to exercise in sHT patients using a standardized protocol and to test the effect of L-T(4) replacement in a double-blind, randomized, placebo-controlled fashion. Patients and Methods: We studied 23 sHT patients and 10 matched euthyroid controls. Oxygen uptake (VO(2)), carbon dioxide output, and heart rate were measured during incremental step-up exercise. Blood glucose, lactate, pyruvate, free fatty acid, glycerol, and beta-hydroxybutyrate concentrations were measured at rest, every 2 min during exercise, and during 20 min of recovery. The exercise protocol was repeated after 6 months of placebo or L-T(4)-restored euthyroidism. Results: Maximal power output ( P = 0.02) and VO(2) max ( P = 0.04) were reduced in sHT, and, with increasing workload, patients achieved higher heart rates ( P < 0.03) at VO(2) values equivalent to those of controls. The respiratory quotient increments were significantly higher in patients than controls ( P < 0.04). Blood lactate and pyruvate and their ratio rose with a steeper slope ( P < 0.0001, P < 0.001, and P < 0.01, respectively) in patients than controls. Resting plasma free fatty acid and blood glycerol levels were significantly higher in patients than controls ( P < 0.0003 and P < 0.003, respectively) throughout baseline, exercise, and recovery. L-T(4) replacement, while improving neuromuscular symptoms, did not produce significant changes in the energy or substrate response to exercise. Conclusions: The response to exercise is altered both in terms of tolerance and pattern of substrate utilization in sHT patients. Restoring stable euthyroidism does not correct this defect over a 1-yr period.File | Dimensione | Formato | |
---|---|---|---|
Caraccio.JCEM2005.pdf
solo utenti autorizzati
Tipologia:
Versione finale editoriale
Licenza:
NON PUBBLICO - Accesso privato/ristretto
Dimensione
306.77 kB
Formato
Adobe PDF
|
306.77 kB | Adobe PDF | Visualizza/Apri Richiedi una copia |
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.