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

Area of Science:

• Endocrinology
• Neuroendocrinology

Background:

• Acromegaly is characterized by excessive growth hormone (GH) secretion, leading to elevated insulin-like growth factor-I (IGF-I) levels.
• Octreotide, a somatostatin analog, is a common treatment for acromegaly, effectively reducing GH and IGF-I.
• The effect of octreotide on the pulsatile secretion of thyroid-stimulating hormone (TSH) in acromegaly is not well understood.

Purpose of the Study:

• To investigate the impact of octreotide therapy on the pulsatile secretion of TSH in patients with active acromegaly.
• To assess changes in TSH pulse parameters, including frequency, amplitude, and timing, before and during octreotide treatment.

Main Methods:

• Eight patients with active acromegaly were studied before and after 1 month of subcutaneous octreotide infusion (300 µg/day).
• Blood samples were collected for analysis of GH, IGF-I, TSH, T3, T4, and reverse T3 (rT3) levels.
• TSH secretion patterns were analyzed using cluster analysis to determine pulse parameters.

Main Results:

• Octreotide therapy significantly reduced mean GH and IGF-I levels (P < 0.01).
• TSH pulse frequency, width, height, and increment remained unchanged during octreotide therapy.
• No significant changes were observed in TSH pulse acrophase, although nocturnal pulse amplitude increased in both treated and untreated patients.
• Triiodothyronine (T3) levels decreased, while reverse T3 (rT3) levels increased during octreotide therapy; T4 levels remained unchanged.

Conclusions:

• The TSH pulse generator in active acromegaly is not significantly altered by chronic octreotide infusions.
• Octreotide's primary effects are on GH and IGF-I regulation, with minimal impact on the TSH secretory system's pulsatility.