Diminished and irregular thyrotropin secretion with preserved diurnal rhythm in patients with active acromegaly.
BACKGROUND
The hypothalamo-pituitary-thyroid axis in acromegaly may be altered. Previous studies report diminished serum TSH concentrations in patients with active acromegaly and decreased response to TRH. On the other hand, most patients have normal thyroid hormone concentrations.


OBJECTIVE
Our aim was to analyze serum TSH profiles in relation to GH profiles in patients with untreated acromegaly, in order to delineate aberrations in the hypothalamo-pituitary-thyroid system.


METHODS
Twenty-one patients with active acromegaly and matched controls underwent a 24-h, 10-min blood sampling study. GH and TSH data were analyzed with a newly developed automated deconvolution program, approximate entropy, and cosinor regression.


RESULTS
Basal (10.4 +/- 2.0 vs. 13.8 +/- 1.4 mU/liter . 24 h; P = 0.02) and pulsatile (11.4 +/- 1.7 vs. 18.6 +/- 1.6 mU/liter . 24 h; P = 0.002) TSH secretion was decreased in patients. TSH secretory regularity was diminished with loss of pattern synchrony between TSH and GH. Total TSH secretion correlated with TSH increase after TRH (R = 0.75; P = 0.0001), negatively with the log-transformed GH secretion rate (R = -0.52; P = 0.001), but not with adenoma size. The diurnal TSH rhythm was preserved. Total and free T4 concentrations were similar in patients and controls.


CONCLUSIONS
Basal and pulsatile TSH secretion is decreased in active acromegaly, although T4 levels are unaffected. Diminished TSH secretion is compatible with enhanced restraint by tumoral GH feedback-driven somatostatin outflow, explaining also the reduced regularity of TSH secretion. Unchanged T4 concentrations might reflect decreased sympathetic function in GH excess states, heightening responsiveness of the thyroid gland to TSH.
Roelfsema
Ferdinand
F
Leiden University Medical Center, Department of Endocrinology and Metabolic Diseases, P.O. Box 9600, Leiden 2300 RC, The Netherlands. f.roelfsema@lumc.nl
Biermasz
Nienke R
NR
Frolich
Marijke
M
Keenan
Daniel M
DM
Veldhuis
Johannes D
JD
Romijn
Johannes A
JA