A Critical Evaluation of the “TRF” of Shibusawa

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Abstract
A supply of "TRF" [thyrotrophin releasing factor] provided oy Dr. K. Shibusawa was tested for thyroid-stimulating and/or thyrotropin-releasing activity in rats and mice. The material in the dosage used failed to affect thyroid weight, plasma PBI, 24-hr thyroid I131 uptake and thyroidal I131 release rate of rats. The material did not cause activation of the thyroid gland in the I131 pre-treated mouse, as measured by changes in blood radioactivity. When tested in the McKenzie mouse system (I131 and thyroxine pretreatment), slight thyroid-stimulating activity was observed equivalent to a fraction of a milliunit per mg of dry material. It is concluded that the "TRF" tested did not possess significant thyrotropin-releasing activity. It is suggested that the designation TRF for hypothetic thyrotropin-releasing factor should be retained in use, but that this term should cover any and all thyrotropin-releasing factors which may be described.