The effect of growth hormone replacement on the thyroid axis in patients with hypopituitarism: in vivo and ex vivo studies.
Level 4 - case-series / case-control
Prospective single-arm before-and-after observational study without a control group
PubMed 27809356 · doi:10.1111/cen.13272
What was done
A prospective observational study evaluated 20 adult men with hypopituitarism receiving growth hormone (GH) replacement as part of routine care (mean daily dose 0.34 ± 0.11 mg). Serum TSH, free and total T4, free and total T3, reverse T3, thyroglobulin, and thyroid-binding globulin (TBG) were measured before and after GH substitution. Subcutaneous adipose tissue biopsies were analyzed ex vivo for deiodinase isoenzyme activity (DIO1, DIO2, and DIO3).
What was found
Following GH replacement: - Free T4 declined significantly (-1.09 ± 1.99 pmol/l, P = 0.02). - Reverse T3 declined significantly (-3.44 ± 1.42 ng/dl, P = 0.03). - Free T3 increased significantly (+0.34 ± 0.15 pmol/l, P = 0.03). - Subcutaneous adipose DIO2 activity declined, whereas DIO1 and DIO3 activities remained unchanged. - Serum TSH, thyroglobulin, and TBG levels showed no significant change.
Why it matters
The findings confirm that GH replacement enhances peripheral conversion of T4 to T3 in hypopituitarism, but indicate that subcutaneous adipose tissue deiodinase changes do not explain these circulating shifts, pointing toward other tissue sites such as liver or muscle.
Limits
Small sample size limited exclusively to 20 adult men. There was no control or placebo group. Tissue enzyme activity was sampled only from subcutaneous fat rather than liver or skeletal muscle, where the bulk of systemic thyroid hormone conversion occurs.
Cited by
- supports Growth hormone promotes the conversion of T4 to T3.