SOME FACTORS INFLUENCING TRH BIOASSAY IN MICE

Abstract

ABSTRACT In a search for optimal conditions for TRH bioassay by the McKenzie method, the effect of dietary iodine, triiodothyronine (T3) and ambient temperature were studied in female mice. Responses to TRH were so sensitive to T3 that even endogenous thyroid hormones interfered with the assay. A low-iodine diet for 2 weeks and an ambient temperature of 7°C for the last 5 days sensitized the mice to TRH. The TRH responses were maximal when 0.1 μg T3 was given 24 h previously with 131I. The smallest detectable dose of TRH was about 1 ng. With this modification the bioassay can detect both TRH and TSH. The responses due to these 2 hormones can be separated by giving different doses of T3 as pretreatment. It is concluded that each laboratory must study its own local conditions for optimal TRH bioassay.