GLOSSARY

Thyrotropin-releasing hormone (TRH) is the smallest hypothalamic peptide hormone (three amino acids: pyroglutamyl-histidyl-prolinamide), secreted from the paraventricular nucleus; it stimulates TSH and, to some extent, prolactin secretion from the anterior pituitary.

Regulation

• Stimulation: cold (especially in newborns) and neural inputs.
• Inhibition: T3 and T4 (negative feedback), somatostatin, cortisol, fasting, and energy deficiency (low leptin).
• Rhythm: TSH is higher at night and in the early morning.

Other Effects

TRH acts as a neurotransmitter in the brain, with mild antidepressant and stimulant effects reported.

Clinical Application