Pulsatile thyrotropin release and thyroid function in acromegalics before and during subcutaneous octreotide infusion.

The pulsatile secretion of TSH was studied in eight patients with active acromegaly before treatment and after 1 month of therapy consisting of the sc infusion of 300 micrograms octreotide/day. Mean GH levels decreased from 37.1 +/- 7.2 to 5.2 +/- 1.4 mU/L (P = 0.002). Insulin-like growth factor-I levels decreased from 82.9 +/- 8.8 to 37.8 +/- 9.8 nmol/L (P less than 0.01) and normalized in five of the eight patients. In one patient TSH levels were undetectable before and during octreotide therapy. In the other seven patients, Cluster analysis revealed 11.9 +/- 0.8 pulses/24 h, with a mean pulse width of 81 +/- 4.6 min, a mean pulse height of 1.33 +/- 0.42 mU/L, and a mean pulse increment of 0.36 +/- 0.12 mU/L. During octreotide therapy these pulse parameters remained unchanged. Pulse height and amplitude increased significantly during the night (i.e. from 2000-0800 h) in both untreated and treated patients. The acrophase was unchanged by therapy. During therapy T3 levels decreased from 2.05 +/- 0.17 nmol/L to 1.44 +/- 0.08 nmol/L (P = 0.001), while rT3 levels increased from 0.14 +/- 0.02 nmol/L to 0.19 +/- 0.03 nmol/L (P less than 0.05). Plasma T4 levels remained unchanged. From these studies we conclude that the TSH pulse generator is unchanged in active acromegaly and apparently unaffected by chronic octreotide infusions.