for anyone who has time to read some research...this is what i pulled as of march of 2003.
J Gerontol 1993 Jul;48(4):M134-9 Related Articles, /entrez/query/static/popup.html/entrez/query/static/popup.htmlLinks
The influence of age on endocrine responses to ultraendurance stress.
Malarkey WB, Hall JC, Rice RR Jr, O'Toole ML, Douglas PS, Demers LM, Glaser R.
Department of Internal Medicine, Ohio State University.
BACKGROUND. Aging produces significant changes in the human endocrine system. This study was designed to determine if elderly and younger individuals differ in various endocrine measures before and after ultraendurance stress. METHODS. Sixteen young and 19 older subjects competing in a world championship triathlon had blood samples acquired for 13 hormones before, immediately after the event, and 18 hours into recovery. RESULTS. Following the triathlon, almost every hormone level increased. Significantly higher basal circulating levels of dihydroepiandrosterone sulfate (DHEA-S) and thyroid stimulating hormone (TSH) were found in 20-year-old individuals, whereas higher levels of norepinephrine (NEPI) and sex hormone binding globulin (SHBG) were found in the 50- to 74-year-old group. Older subjects had lower postexercise levels of EPI, DHEA-S, GH, and PRL and higher postexercise levels of estradiol than younger individuals. Similarity in pre- and postrace weights as well as Hgb and Hct levels suggested that dehydration, while present, did not significantly contribute to the endocrine changes. CONCLUSIONS. Ultraendurance stress produced dramatic increases in all but one of the hormones evaluated. Whether frequent exercise can alter the endocrine changes that occur with aging cannot be answered by this study. It is clear, however, that when comparisons are made with young active individuals, frequent exercise does not eliminate the differences in basal concentrations of TSH, DHEA-S, SHBG, and NEPI or exercise-induced release of estradiol, GH, and PRL that occur with aging.
Clin Endocrinol (Oxf) 1992 Oct;37(4):325-30
The effect of endurance training on serum triiodothyronine kinetics in man: physical conditioning marked by enhanced thyroid hormone metabolism.
Rone JK, Dons RF, Reed HL.
Department of Endocrinology & Metabolism, Wilford Hall USAF Medical Center, Lackland Air Force Base, Texas.
OBJECTIVE: We studied the relationship between endurance training, aerobic capacity, and T3 metabolism in healthy euthyroid men. DESIGN: T3 kinetic studies performed on two groups of subjects differentiated on the basis of physical activity status and aerobic capacity. SUBJECTS: Five endurance-trained athletes and five sedentary controls (mean +/- SD VO2 max = 48.2 +/- 7.1 vs 23.2 +/- 4.5 ml/kg/min, respectively) matched for age, body surface area, lean body mass, and baseline thyroid function. MEASUREMENTS: Kinetic analysis performed using serial serum T3 levels measured following oral T3 administration. Metabolic clearance rate, total volume of distribution, disposal rate, and total body pool calculated using non-compartmental analysis. RESULTS: When normalized for lean body mass, all kinetic parameters were 25-38% greater in the athletic group compared to controls (P < 0.05). Total volume of distribution, disposal rate, and total body pool were positively correlated with aerobic capacity (r = +0.69 to +0.79; P < 0.05). Metabolic clearance rate was positively correlated to a non-significant degree. CONCLUSIONS: These results confirm the findings of prior studies that thyroid hormone metabolism is altered by physical conditioning. In addition, we demonstrated a positive correlation between aerobic capacity and several parameters of T3 kinetics. Differences in absolute lean body mass cannot explain these findings; rather it appears that there is something qualitatively different in the way endurance-trained tissue processes thyroid hormone, compared to untrained tissue. The study was not designed to elucidate these differences at the cellular level; however, it does support a link between muscle physiology and T3 activity and may suggest a physiological role for thyroid hormone in physical conditioning.
J Sports Med Phys Fitness 1991 Jun;31(2):142-6
Serum thyroid hormones, thyrotropin and thyroxine binding globulin in elite athletes during very intense strength training of one week.
Pakarinen A, Hakkinen K, Alen M.
Department of Clinical Chemistry, University of Oulu, Finland.
The effects of a one-week very intense strength training period on maximal strength and pituitary-thyroid function were investigated in eight elite male weight lifters. No statistically significant changes occurred in the maximal isometric leg extension force of the test subjects. Decreased serum concentrations of thyrotropin (TSH), thyroxine (T4) and triiodothyronine (T3) were found during the training period, but no statistically significant changes occurred in the levels of free thyroxine (fT4), reverse T3 (rT3) and thyroxine binding globulin (TBG). The results suggest that the training stress affects at the hypophyseal and/or hypothalamic level decreasing the secretion of TSH, which leads to slightly decreased function of the thyroid gland.
Exp Clin Endocrinol 1989 Sep;94(1-2):82-8
Thyroid hormone metabolism under extreme body exercises.
Hesse V, Vilser C, Scheibe J, Jahreis G, Foley T.
Division for Paediatric Endocrinology, Children's Hospital, University of Jena, GDR.
In two runs over a distance of 75 km and 45 km as well as in a marathon (42.2 km), the thyroid hormones (T4, T3 and TSH in all runs and rT3 in two of them) were determined before and after the runs. The performance of the runners was analyzed, with their age considered in the analysis. We found that the changes of thyroid hormones are characterized by individual differences. Younger runners and those with better performances had significantly higher T4 serum concentrations and unaltered T3 and TSH concentrations, whereas older sportsmen and those with worse performances reacted to the stressful stimulus with a significant decrease of T4, T3 and TSH. This response was interpreted as an exhaustion reaction, i.e. reduced adaptation responses of thyroid hormone metabolism. Therefore, these investigations provide an assessment of the state of fitness, the optimization of training and the avoidance of damage caused by overly stressful physical exercise
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Acta Endocrinol (Copenh) 1987 Jan;114(1):41-6
Serum concentrations of thyrotropin, thyroxine, triiodothyronine and thyroxine binding globulin in female endurance runners and joggers.
Hohtari H, Pakarinen A, Kauppila A.
The effects of endurance training and season on the function of the anterior pituitary-thyroid axis were studied in 18 female runners and their 12 controls, and in 13 joggers and their 11 controls in Northern Finland, with a large seasonal difference in environmental factors. The serum concentrations of thyrotropin (TSH), thyroxine (T4), free thyroxine (fT4), triiodothyronine (T3), thyroxine binding globulin (TBG) and oestradiol (E2) were measured during one menstrual cycle in the light training season (autumn) and in the hard training season (spring). The responses of TSH to intravenous TRH stimulation were also measured in the luteal phase of the cycle during the hard training season. Endurance running did not affect the basal or TRH-stimulated serum TSH concentrations, while those of T4 and fT4 in runners were lowered in both seasons and that of T3 in the light training season in relation to control subjects. The serum concentrations of TBG were also significantly lower in runners than their controls in the luteal phase in both seasons. The effect of jogging on thyroid hormones was less pronounced. Serum concentrations of TSH, T4, fT4, T3 and TBG were generally slightly higher in spring than in autumn. Strenuous endurance training seems to have minor changes on the function of the thyroid gland. Depressed T4 levels in runners may rather be due to lowered TBG levels than due to direct effect of training. In spring the function of anterior pituitary-thyroid axis is more active than in autumn.
Med Sci Sports Exerc 1984 Jun;16(3):243-6
Thyroidal changes associated with endurance training in women.
Boyden TW, Pamenter RW, Rotkis TC, Stanforth P, Wilmore JH.
The associations between endurance training, body composition, and the pituitary-thyroid axis were studied in 17 healthy, young women. Body composition and plasma concentrations of T4, T3, rT3, resin T3 uptake, TSH, and TRH-stimulated TSH were examined at baseline and after each subject's weekly distance had increased 48 km (delta 48) and 80 km (delta 80) above baseline. Total body weight did not change at delta 48 or delta 80. Mean (+/- SE) lean weight in kg increased from 42.9 +/- 1.2 at baseline to 44.8 +/- 1.2 at delta 80 (P = 0.002). We have reported previously that at delta 48 the subjects had evidence of mild thyroidal impairment, which consisted of decreased T3 and rT3, and an exaggerated TSH response to TRH. With more prolonged training (delta 48 to delta 80) there were significant increases in T4, rT3, and unstimulated TSH, while the ratios of T4/rT3 and T3/rT3 and the TSH response to TRH decreased significantly. Some of the thyroidal changes that occurred between delta 48 and delta 80 are similar to those seen in other stressful non-thyroidal conditions.
J Clin Endocrinol Metab 1982 Jan;54(1):53-6
Evidence for mild thyroidal impairment in women undergoing endurance training.
Boyden TW, Pamenter RW, Stanforth P, Rotkis T, Wilmore JH.
The effects of endurance training on body composition and the pituitary-thyroid axis were studied in 29 healthy, young (mean age, 28.7 yr), regularly menstruating women. Women who were initially jogging a mean of 13.5 miles/week were selected for this study to minimize dropouts. Body composition, measured by hydrostatic weighing, and nonfasting plasma concentrations of T4, T3, rT3, TSH, and TRH-stimulated TSH, measured by RIA, were examined initially and after each subject's weekly mileage had increased to 30 miles ( delta 30) for at least 2 consecutive weeks. Two subjects were found to have compensated primary hypothyroidism and were not included in the subsequent data analysis. At delta 30, mean body weight did not change, mean fat weight decreased (- 1.02 kg; P less than 0.005), and mean lean weight increased (+0.75 kg; P less than 0.05). T4 and unstimulated TSH did not change. However, mean (+/-SE) T3 decreased from 107.2 +/- 4.4 to 97.9 +/- 3.4 ng/dl (P less than 0.025), and mean rT3 decreased from 170.9 +/- 13.9 to 154.6 +/- 13.2 pg/ml (P less than 0.025). The decreases in T3 and rT3 were accompanied by significantly greater TSH responses to TRH stimulation [mean (+/-SE) area under TSH curve, 1381.4 +/- 123 vs. 1712.8 +/- 202 micron IU/ml.min; P less than 0.01]. These results indicate that physically active women who undergo additional endurance training 1) become more lean without a change in total weight, and 2) have changes in T3, rT3, and TRH-stimulated TSH indicative of mild thyroidal impairment.
J Clin Endocrinol Metab 1997 Oct;82(10):3315-8 Related Articles, Links
J Clin Endocrinol Metab. 1998 May;83(5):1823.
Clinical and biochemical features of muscle dysfunction in subclinical hypothyroidism.
Monzani F, Caraccio N, Siciliano G, Manca L, Murri L, Ferrannini E.
Department of Internal Medicine, University of Pisa, Italy.
Alterations in muscle structure and function have been reported in overt hypothyroidism, with decreased activity of enzymes involved in anaerobic and oxidative glucose metabolism. To test whether similar changes in muscle energy metabolism are present in subclinical hypothyroidism (sHT), we studied 12 patients with sHT who complained of mild neuromuscular symptoms. The control group included 10 sex- and age-matched healthy volunteers. Skeletal muscle lactate and pyruvate production were determined in the resting state and during dynamic arm exercise. During exercise, blood lactate was significantly higher in sHT patients than in controls from the third exercise step onward (P = 0.02 at 30%, p = 0.008 at 40%, and P = 0.002 at 50% of maximal voluntary contraction). Moreover, the mean increment in blood lactate during exercise was positively related (r2 = 0.44; P = 0.02) to the duration of sHT, but not to serum levels of TSH, free T3, or free T4. No significant difference was found in blood pyruvate concentrations between the two groups at baseline or during exercise. Thus, the lactate/pyruvate ratio curve paralleled the lactate curve in patients as well as controls. We conclude that muscle energy metabolism is impaired in sHT in rough proportion to the known duration of the disease. Early L-T4 therapy may be useful not only to provide specific treatment for such metabolic changes, but also to avoid progression to frank hypothyroidism.
PMID: 9329360 [PubMed - indexed for MEDLINE]
J Physiol Pharmacol 1996 Sep;47(3):503-13 Related Articles, Links
Influence of thyroid hormones on exercise tolerance and lactate threshold in rats.
Zarzeczny R, Pilis W, Langfort J, Kaciuba-Uscilko H, Nazar K.
Department of Physical Education, University of Pedagogics, Czestochowa, Poland.
Effects of thyroid hormone deficit, and triiodothyronine (T3) treatment on exercise performance, blood lactate (LA) concentrations and LA threshold (TLA) were studied in trained and untrained rats. Fourteen rats were thyroidectomized and then treated with propylthiouracil for 30 days (THY + PTU group). Fourteen sham operated rats served as controls. In each group there were 7 sedentary and 7 endurance-trained animals. Six weeks after thyroidectomy or sham operation the rats were subjected to a multistage running test with speed increasing from 13 m/min at 10 degrees treadmill inclination till maximum. Blood samples for LA were taken from the rats' tail after each 3-min exercise stage. During 3 days following this test rats from all groups were injected (i.p.) with 75 micrograms/100 g of triiodothyronine (T3), and 24 hrs afterwards the second exercise test was performed. In THY + PTU rats maximal running speed (RSmax) and the speed at which TLA occurred were markedly decreased in comparison with control group. The level of LA at the maximal speed (LAmax) and that corresponding to TLA were higher in THY + PTU rats than in controls. T3 injection to control animals diminished their RSmax and TLA, whereas in THY + PTU rats it increased RSmax and shifted TLA to a higher speed. Both in THY + PTU and control animals T3 elevated LAmax and the threshold LA concentration. Endurance training in control and THY + PTU animals markedly enhanced RSmax and TLA. This was accompanied by increases in LAmax and concentration of LA at TLA only in control group. After T3 injection to control trained rats RSmax and TLA were diminished, whereas in THY + PTU trained group RSmax was unchanged and TLA was elevated. Maximal blood LA increased only in THY + PTU trained rats whilst the threshold blood LA was elevated in both groups. It is concluded, that both the T3 deficiency and its excess reduce maximal exercise performance and shift TLA to lower workloads. Enduarance training or administration of T3 to hypothyroid rats markedly improve their exercise performance and elevate TLA, however, T3 treatment markedly increases maximal and submaximal LA levels.
J Endocrinol Invest 2002 Feb;25(2):106-9 Related Articles, Links
Levothyroxine therapy and serum free thyroxine and free triiodothyronine concentrations.
Woeber KA.
Department of Medicine, University of California, San Francisco/Mount Zion, San Francisco 94143-1640, USA.
woeber@itsa.ucsf.edu
Although the normal thyroid gland secretes both levothyroxine (L-T4) and levotriiodothyronine (L-T3), normalization of serum TSH with L-T4-replacement therapy alone in hypothyroidism is generally believed to result in a normal serum L-T3 and to reflect a euthyroid state. However several recent studies suggest that this may not be the case. Accordingly, the relationship between serum free L-T4 and free L-T3 was examined in 20 normal individuals (group A) and in 53 patients with chronic autoimmune thyroiditis, 18 with normal TSH on no L-T4-replacement (group B), and 35 with normal TSH on L-T4-replacement therapy for hypothyroidism (group C). Data were analyzed by applying a one-way analysis of variance with correction for multiple comparisons. Serum TSH values were very similar among the 3 groups. In groups A and B, mean serum free T4 and free T3 were very similar. In group C, the mean free T4 (16+/-2 pmol/l) was significantly higher than the values in groups A (14+/-1) and B (14+/-2) (p<0.001) and the mean free T3 lower (4.0+/-0.5 pmol/l vs 4.2+/-0.5, NS and 4.4+/-0.5, p<0.02). Consequently, the mean molar ratio of free T4 to free T3 was significantly higher in group C than the ratios in groups A and B (p<0.0001), despite very similar TSH values. These findings indicate that in hypothyroid patients L-T4-replacement, that is sufficient to maintain a normal serum TSH, is accompanied by a serum free T4 that is higher than that in untreated euthyroid patients or normal individuals and may not result in an appropriately normal serum free T3 concentration.