Cortisol Lowers TSH - Can Make Hypo Thyroid Person Seem "normal"

[ecstatichamster]

Thyrotropin Levels during Hydrocortisone Infusions That Mimic Fasting-Induced Cortisol Elevations: A Clinical Research Center Study 1

Both short term fasting and administration of high doses of glucocorticoids lead to marked suppression of serum TSH levels in healthy subjects.

However, it is not known whether the more mild serum cortisol elevations seen during fasting can account for fasting-induced TSH suppression.

To study this question, eight healthy subjects each underwent three 2-day studies: 1) baseline (ad libitum diet), 2) fasting (56 h of total caloric deprivation), 3) hydrocortisone (HC) infusions at a dose and pulsatile pattern that reproduced cortisol levels measured during each subject’s fasting study. Subjects required 34–46 mg HC/24 h to achieve these cortisol levels.

During each study, blood samples were drawn every 15 min during the final 24 h for serum cortisol and TSH levels. A TRH stimulation test was performed at the end of each study. By design, fasting and HC infusions induced similar mild increases in 24-h serum cortisol levels (32% over baseline), with the most significant increases seen between 1400–0200 h.

Fasting decreased 24-h mean and pulsatile TSH levels 65% from baseline, whereas HC infusions decreased mean and pulsatile TSH levels 51% from baseline. Daytime (0800–0200 h) TSH levels were identical in the two studies, whereas nocturnal (0200–0800 h) TSH levels during HC infusions fell midway between baseline and fasting studies.

Serum total T3 and TSH responses to TRH were decreased to a similar degree by fasting or HC infusions. These results suggest that mild elevations in endogenous cortisol levels may mediate at least in part fasting-induced changes in TSH secretion and thyroid hormone levels. In addition, these data show that near-physiological doses of HC and resulting changes in serum cortisol levels within the normal range can cause significant decreases in serum TSH levels.

 

[ecstatichamster]

Effect of Glucocorticoid Administration on Human Pituitary Secretion of Thyrotropin and Prolactin

In order to determine the mechanism by which glucocorticosteroids decrease the serum concentration of thyrotropin (TSH), we studied eight normal subjects before and after they received 16 mg of dexamethasone daily for 2½ days. Serum levels of TSH and prolactin (PRL) were measured in the basal state and in response to the intravenous administration of 200 μg thyrotropinreleasing hormone (TRH); T4, free T4 (fT4), T3, and free T3 (fT3) were measured before TRH injection. Metabolic clearance rates of TSH corrected for body surface area (MCR-TSH/m2) were determined by the method of constant infusion to equilibrium; the production rates of TSH (PR-TSH/m2) were calculated. Dexamethasone produced a decrease in basal TSH from 2.2 to 0.8 μU/ml (P < 0.02), a statistically insignificant elevation in MCR-TSH/m2 from 25.8 to 34.1 ml/min/m2, and a decrease in PRTSH/m2 from 79 to 30 mU/day/m2 (P < 0.01). Peak TSH response to TRH decreased from 16.4 to 5.8 μU/ml (P < 0.005), as did TSH reserve from 1.58 to 0.54 mU · min/ml (P < 0.005). Repetitive TRH testing alone did not account for these changes. Basal PRL, peak PRL after TRH, and PRL reserve did not change significantly after dexamethasone administration. Although Basal T4and fT4 did not change significantly, dexamethasone did decrease T3 from 106 to 61 ng/dl (P < 0.001) and fT3 from 174 to 76 pg/dl (P < 0.05). Dexamethasone produced similar changes in patients with various thyroid disorders. In addition, when plasma cortisol was lowered by metyrapone administration in 25 euthyroid patients, the serum TSH concentration rose from 1.6 to 3.1 μU/ml (P < 0.001).

These data indicate that dexamethasone a) suppresses TSH secretion without increasing fT3 and fT4 and b) blunts the TSH, but not the PRL response, to TRH. Hence, one effect of the administration of dexamethasone in high dose is a direct suppression of pituitary TSH secretion. Furthermore, physiologic levels of circulating cortisol also have a suppressive effect on serum TSH.

 

[ecstatichamster]

good evidence that relying on TSH for thyroid treatment is completely bogus.

 

[ebs]

Interesting. I was of the believe from reading on this forum that high cortisol caused elevated TSH, but perhaps I'm confused with cortisol supressing T3. Aren't there studies that show stress elevates TSH?