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

The effect of thyroid hormones (TH) on the metabolism of thyrotropin-r eleasing hormone (TRH) in the olfactory bulb (OB) was compared with th e hypothalamic response to TRH. Two methods were used to induce hypoth yroidism: propylthiouracyl-methimazole (PTU-M) or I-131 treatment. Hyp erthyroidism was produced by 3,3',5-triiodo-L-thyronine (T-3) injectio ns to the hypothyroid animals. With PTU-M treatment, paraventricular T RH 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 un affected in the mediobasal hypothalamus of PTU-M-treated animals where as it was reduced in OB (31%) with no further response upon T-3 treatm ent. I-131-induced hypothyroidism did not modify the OB TRH content bu t 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 c an alter TRH levels in the OB, probably at a translational or postrans lational level, though the effects may be pharmacological.