Production of antisera to growth hormone-releasing factor: usefulness in radioimmunoassay and passive immunization.

We have produced two antisera (R-1 & R-2) to human growth hormone-releasing factor (GRF) [1-44] NH2. Both antisera can be used for human GRF radioimmunoassay (RIA) at a final dilution of 1:50000. The antiserum R-2 was specific for the C-terminal amidated sequence of human GRF-44 and selectively recognized GRF [1-44] NH2 but not GRF [1-44] OH or GRF [1-40] OH. The antiserum R-1 also significantly bound 125I-rat GRF [1-43] OH at a final dilution of 1:5000 and enabled us to establish RIA for rat GRF. In both RIA systems, intra- and inter-assay coefficients of variation at 50% inhibition were 8 and 12%, respectively. A median effective dose was 90-120 pg in human GRF RIA and 250-300 pg in rat GRF RIA. Utilizing the RIA, we demonstrated that the hypothalamic GRF content in rats which received monosodium glutamate during the neonatal period was less than 20% of that of controls. However, the hypothalamic GRF content was not altered in rats made hypothyroid by methimazole administration, another condition known to greatly impair GH secretion. An iv administration of the antiserum R-1 significantly suppressed GH release following the injection of antisomatostatin serum. Thus, these antisera can be a useful tool in examining the physiological and/or pathophysiological roles of GRF in human and rat.