Effects of morphine on the pituitary-thyroid axis: morphological and analytical studies.

The morphology of the TSH-producing pituitary cells and the thyroid gland, and plasma TSH, T3 and T4 hormone levels, were studied in normal rats, in rats treated with 10 micrograms morphine (M) and in M-treated animals pretreated with naloxone (Nx) (10 mg/kg). Morphological changes in the pituitary TSH cells and thyroid cells of M-treated animals were minimal and were not modified by Nx pretreatment. Plasma TSH levels in M-treated animals showed a significant decrease (P less than 0.05), which was not blocked by Nx pretreatment. No significant changes in plasma T3 or T4 levels were found in either experimental group.