INFLUENCE OF THYROID STATUS ON TRH METABOLISM IN RAT OLFACTORY-BULB

The effect of thyroid hormones (TH) on the metabolism of thyrotropin-releasing hormone (TRH) in the olfactory bulb (OB) was compared with the hypothalamic response to TRH. Two methods were used to induce hypothyroidism: propylthiouracyl-methimazole (PTU-M) or I-131 treatment. Hyperthyroidism was produced by 3,3',5-triiodo-L-thyronine (T-3) injections to the hypothyroid animals. With PTU-M treatment, paraventricular TRH mRNA levels increased 57% and returned to the euthyroid level with T-3 treatment. In OB, TRH mRNA was not altered. The TRH content was unaffected in the mediobasal hypothalamus of PTU-M-treated animals whereas it was reduced in OB (31%) with no further response upon T-3 treatment. I-131-induced hypothyroidism did not modify the OB TRH content but it was decreased (31%) in hyperthyroids. In the median eminence, TRH increased 26% in hypothyroids, and the response was reversed with T-3. Our results demonstrate that treatments that change thyroid status can alter TRH levels in the OB, probably at a translational or postranslational level, though the effects may be pharmacological.