Effect of caffeine on thyroid and pituitary function in newborn rats

Area of Science:

• Endocrinology
• Neonatal Pharmacology
• Neuroendocrinology

Background:

• Caffeine is a central nervous system stimulant used for neonatal apnea.
• Potential effects of caffeine on neonatal endocrine function are not fully understood.
• This study investigates caffeine's impact on key hormones in newborn rats.

Purpose of the Study:

• To examine acute and chronic effects of caffeine on growth hormone (GH), thyroxine (T4), and thyrotropin (TSH) in newborn rats.
• To assess caffeine's influence on basal hormone levels and hormone responses to stimulation.

Main Methods:

• Five-day-old rats received saline (control), low-dose (5 mg/kg), or high-dose (50 mg/kg) caffeine daily for 10 days.
• Hormone levels (GH, T4, TSH) were measured via radioimmunoassay at various time points after single or repeated injections.
• Caffeine levels were quantified using high-pressure liquid chromatography.

Main Results:

• Acute caffeine administration increased GH levels at all tested doses and time points.
• Chronic high-dose caffeine showed a biphasic effect on T4, increasing it at 4 hours and decreasing it at 24 hours.
• Chronic caffeine therapy elevated basal T4 and TSH levels, but decreased the TSH response to thyrotropin-releasing hormone (TRH).

Conclusions:

• Acute caffeine increases GH in newborn rats, potentially indicating pituitary reserve depletion with chronic use.
• Chronic caffeine exposure stimulates T4 and TSH production but may impair the pituitary's ability to release TSH in response to TRH.
• These findings suggest caffeine can alter neonatal endocrine regulation, with implications for its therapeutic use.