Anin VivoAssay for Thyrotropin Releasing Factor

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Abstract
An in vivo method for assaying thyrotropin releasing factor (TRF) in mice has been described. Administration of codeine to mice given 131l and 1 [mu]g thyroxine increased the responsiveness of the pituitary to TRF preparations. There was a linear relationship between the log dose of TRF and the increase in blood radioactivity. When TSH is assayed by this method the dose-response range is linear from 0.05 to 0.8 mU with an index of precision ([lambda]) of 0.2. Purified TRF preparations of porcine, ovine, bovine and human origin raised blood 1311 levels in the thyroxine-codeine treated mice but not in hypophysectomized mice prepared in the same manner. These same TRF preparations were also inactive in mice pretreated with large amounts of thyroxine. Doses of vasopressin, [alpha]- and [beta]-MSH [melanocyte stimulatory hormone] known to release 131l from the thyroid gland in mice prepared for the McKenzie TSH assay, did not elicit a significant response in mice given codeine and 1 [mu]g of thyroxine. These results obtained in the codeine-thyroxine assay are in agreement with in vitro data and in vivo plasma TSH levels.