Effects of cimetidine on thyroid hormones

Area of Science:

• Endocrinology
• Pharmacology

Background:

• Cimetidine is an H2-antagonist with potential endocrine effects.
• Thyroid hormones (T3, rT3, T4) and pituitary hormones (TSH, prolactin) are crucial for metabolic and physiological regulation.
• Acute hypoglycemia and thyrotropin-releasing hormone (TRH) are standard stimuli to assess pituitary hormone release.

Purpose of the Study:

• To investigate the effects of short-term cimetidine administration on thyroid hormone levels.
• To evaluate the impact of cimetidine on pituitary hormone release in response to acute hypoglycemia and TRH stimulation.

Main Methods:

• Eight healthy male volunteers received cimetidine (400 mg TID for 5 days).
• Serum levels of thyroid hormones (T3, rT3, T4) and pituitary hormones (prolactin, TSH) were measured.
• Hormonal responses were assessed under basal conditions, after TRH stimulation, and during acute hypoglycemia.

Main Results:

• Cimetidine significantly decreased basal and post-TRH serum T3 levels.
• Basal and stimulated serum rT3 and T4 levels remained largely unchanged.
• Cimetidine did not affect hormone release during hypoglycemia but enhanced prolactin and TSH responses to TRH.

Conclusions:

• Short-term cimetidine administration appears to modify peripheral thyroid hormone metabolism, specifically T3 levels.
• Cimetidine enhances pituitary responsiveness to TRH, indicated by increased prolactin and TSH release.
• These findings suggest cimetidine's influence on endocrine function extends beyond its H2-antagonist activity.