RADIOIMMUNOASSAY OF THYROTROPHIN RELEASING HORMONE

The ability to assay small amounts of the peptide releasing hormones in biological fluids would aid greatly in the assessment of hypothalamic function. We have recently described a specific radioimmunoassay for luteinizing hormone releasing hormone (LH-RH) (Jeffcoate, Fraser, Gunn & Holland, 1973a, b) and in this study we report a radioimmunoassay for the tripeptide, thyrotrophin releasing hormone (TRH). Thyrotrophin releasing hormone (2 mg) was conjugated to 10 mg bovine serum albumin in borate buffer pH 9·0 by the bis-diazotized benzidene method (Bassiri & Utiger, 1972 a). After 2 h at 5 °C the mixture was dialysed against distilled water for 48 h and against 0·15 m-NaCl for 24 h. This technique conjugates TRH by the imidazole ring of histidine to the protein. A sample of conjugate (2·5 mg) in saline was homogenized with Freund's complete adjuvant and injected into 20 intradermal sites in a White New Zealand rabbit.