EVALUATION AND CHARACTERIZATION OF CONGENITAL HYPOTHYROIDISM IN RDW DWARF RATS

The rdw rat is a new strain of dwarf mutant that has decreased blood t hyroxine (T-4) and growth hormone (GH) concentrations and testicular e nlargement during development and aging. To confirm whether this strai n can be used as a new hypothyroid model, the experiments reported her e were carried out, using adult rdw rats, rdw rats treated with thyrox ine, and clinically normal (N) Wistar-Imamichi rats. Clinical paramete rs of deficient thyroid function in rdw rats were chosen for evaluatio n and characterization. Body weight, hemoglobin (Hb) concentration, he matocrit (Hct), glucose (GLU), and systolic blood pressure were signif icantly lower, and serum values for aspartate transaminase (AST), tota l cholesterol (TC), total protein (TP), and blood urea nitrogen (BUN) were higher in rdw than in N rats. Serum concentrations of total T-4 a nd free triiodothyronine (FT3) were significantly lower, and serum thy roid-stimulation hormone (TSH) concentration was markedly higher in rd w than in N rats. Serum GH concentration was significantly lower in rd w than in N rats. Results of histologic examination indicated that the thyroid gland of rdw rats was markedly atrophied, compared with that of N rats. Results of clinical examination of organs and hematologic a nd biochemical values in rdw rats corresponded to those of the hypothy roid state in humans. Most organ weights (heart, kidney, spleen, and a drenal gland), hematologic and biochemical values (Hb, Hct TC, TP, BUN ), blood pressure, and serum hormone (TSH and GH) values underwent sub stantial restoration (partial or complete) toward normal in response t o replacement therapy. In conclusion, the rdw rat is a useful model of congenital hypothyroidism.