Dose-response studies with protirelin

Area of Science:

• Neuroendocrinology
• Psychiatry
• Endocrinology

Background:

• A subset of patients with major depression exhibits a blunted thyrotropin (TSH) response to thyrotropin-releasing hormone (protirelin [TRH]).
• This observation supports the hypothesis of downregulated pituitary TRH receptors in major depression.
• Consequently, attenuated TSH and prolactin (PRL) responses to TRH are predicted.

Purpose of the Study:

• To investigate the dose-response relationship of protirelin-induced TSH and PRL secretion in patients with major depression compared to controls.
• To test the hypothesis of downregulated TRH receptors in major depression by examining TSH and PRL responses.

Main Methods:

• Four ascending doses of protirelin (25-800 mcg) were administered to patients with major depression and age/gender-matched controls.
• TSH and PRL levels were measured post-infusion across different protirelin doses.
• Seven men and seven women with depression were compared to controls.

Main Results:

• No significant baseline differences in thyroid hormones or cortisol between groups.
• Depressed men showed significantly reduced TSH and PRL responses to all protirelin doses compared to control men.
• Depressed women displayed reduced TSH responses but not PRL responses compared to control women.

Conclusions:

• Reduced TSH and PRL responses to protirelin in depressed men support the TRH receptor downregulation hypothesis in depression.
• The less clear findings in women may be attributed to greater variability in PRL responses.
• Further research is needed to clarify the neuroendocrine differences in depression between sexes.