In primary hyperthyroidism, which statement best describes the regulation of TSH and TRH?

In primary hyperthyroidism, which statement best describes the regulation of TSH and TRH?

• A. Both TSH and TRH are elevated.
• B. TSH increases but TRH decreases.
• C. TSH decreases while TRH increases.
• D. Both TSH and TRH are suppressed.

Answer: (D)