Radioimmunoassay for GH-Release Inhibiting Hormone 1

Summary

The synthetic growth hormone release inhibiting hormone (GH-RIH) was conjugated with human serum globulin using glutaraldehyde and administered to rabbits.

An antiserum thus generated bound 70 % of ¹²⁵I-Tyr¹-GH-RIH. The binding was inhibited by unlabelled GH-RIH and the inhibition was dose-related, enabling us to establish a radioimmunoassay method for GH-RIH. The minimum detectable dose was 4 pg. A linearity was demonstrated for im-munoreactive GH-RIH of extracts of rat and pig hypothalami, indicating that they contained substance(s) indistinguishable from GH-RIH. Various hypothalamic and pituitary hormones did not interfere with the radioimmunoassay, but considerable cross-reaction was observed for linear GH-RIH and the ring portion of GH-RIH, suggesting that the antigenic determinant involved the amino acid sequence from position 3-14 of GH-RIH or part of it. Plasma protein appears to contain substance(s) immunologically indistinguishable from GH-RIH or to interfere, in a nonspecific manner, with the radioimmunoassay system for GH-RIH.

The authors wish to express our thanks to NIAMDD, Rat Pituitary Hormone Program, and Dr. Harold Papkoff for various pituitary hormones, Merck Sharp and Dohme Research Laboratory for GH-RH, Abbott Laboratory for TRH, Ayerst Laboratory for GH-RIH, and Sankyo, Co., for LH-RH.