RADIO-RECEPTOR ASSAY FOR THYROTROPIN RELEASING HORMONE

  • 1 January 1977
    • journal article
    • research article
    • Vol. 38  (4) , 265-271
Abstract
The high affinity receptor for TRH [thyrotropin releasing hormone] of the rat pituitary GH3 strain in culture (Km: 4 .times. 10-9 M) was suitable to design a radioreceptor assay for TRH [thyrotropin releasing hormone]. Attached GH3 cells were incubated for 30 min at 37.degree. C in the presence of a tracer amount of 3H-TRH (200 pg/ml, 0.54 nM) and increasing quantities of cold synthetic TRH. After extensive washings, the radioactivity associated with the cells was counted, and the log-logit transformation was applied to the results expressed as % binding (100%: binding in absence of unlabeled TRH). The standard curve is linear between 200 pg/ml and 5 ng/ml TRH. Hypothalamic or thyroid hormones were tested for their competitive effect with 3H-TRH towards the GH3 cells receptor. None of them interfered. TRH analogs were also assayed for their competition with TRH towards the receptor. Only compounds methylated on prolineamide or histidine could compete with TRH, but these derivatives have never been shown to occur in vivo. Because of this high specificity, this radioreceptor assay was applied to biological samples, extracted once with acidic methanol and purified by CMC [carboxymethyl-cellulose) column.

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