C- and N-terminal specific LH-releasing hormone (LRH) radioimmunoassay

A highly sensitive and specific LRH radioimmunoassay is described. Three antisera were compared and characterized. High specificity was shown by 2 of them in that both C- and N-terminals were required for binding when testing LRH analogs. A lower detection limit of about 1 pg could be obtained using a simple organic solvent precipitation method for separation of bound/free antigen. Good correlation with the Ramirez-McCann bioassay was obtained, and rat median eminence extracts contained a material immunologically similar to synthetic LRH as indicated by parallel inhibition curves. Direct measurement of radioimmunoassayable LRH in plasma can lead to misleading results due to nonspecific interference of plasma factors. After employing a simple deproteinization method, rat plasma was found to contain less than 1-3 pg LRH/ml. Rat median eminence extracts contained approx. 7 ng LRH.