Effect of gamma-oryzanol on serum TSH concentrations in primary hypothyroidism.

A single oral dose (300 mg) of gamma-oryzanol extracted from rice-bran oil produced a significant reduction on the elevated serum TSH levels in hypothyroid patients. Similarly, chronic treatment with gamma-oryzanol resulted in decreased serum TSH levels in 6 of 8 patients. There was no change in the serum levels of thyroxine-iodine and triiodothyronine during the study. In addition, there was no difference in the serum TSH response to TRH in hypothyroid patients and normal subjects. These observations suggest that gamma-oryzanol inhibits serum TSH levels in patients with primary hypothyroidism, possibly by a direct action at the hypothalamus rather than the pituitary.