Key result
Administration of T4 significantly decreased day/night sodium excretion (P<0.01) and increased mean nocturnal heart rate (P<0.01) in normal subjects.
Why the study?
Does administration of T4 alter heart rate and urinary sodium excretion in normal subjects?
Does administration of T4 alter heart rate and urinary sodium excretion in normal subjects?
Answers are grounded in this paper and cite their sources.
Minor increments in plasma thyroxine within the normal range alter heart rate and sodium excretion, suggesting peripheral tissues recognize minor thyroid hormone excess.
We studied day/night (D:N) patterns of urinary sodium excretion and the 24 hour ambulatory electrocardiogram in seven normal subjects before and during the administration of T4. Thyroxine increased thyroid hormone levels within the normal range and inhibited the plasma TSH response to TRH. This was associated with a significant decrease in D:N sodium excretion (P less than 0.01) and D:N urine flow (P less than 0.01), a significant increase in mean nocturnal heart rate (P less than 0.01), and a lesser increment in mean daytime heart rate (P less than 0.05). These responses to small changes in thyroid hormone levels suggest that the anterior pituitary is not alone in recognising minor thyroid hormone excess. The clinical implication is that some patients with a normal T3 and T4 but an impaired TSH response to TRH might benefit from antithyroid treatment.
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Bell et al. (1983) studied Normal subjects (n=7). T4 (Thyroxine) vs. Baseline (before administration) was evaluated on Day/night (D:N) patterns of urinary sodium excretion and mean nocturnal heart rate (p=<0.01). Administration of T4 significantly decreased day/night sodium excretion (P<0.01) and increased mean nocturnal heart rate (P<0.01) in normal subjects.
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