Plasma immunoreactive-growth hormone in domestic fowl: measurement by homologous and heterologous radioimmunoassays.

Concentrations of immunoreactive (IR) growth hormone (GH) in the plasma of domestic fowl have been measured by homologous and heterologous radioimmunoassays and the estimates compared. Both assays detected an age-related decline in the circulating IR-GH concentration, an increase in IR-GH secretion following TRH-stimulation or fasting, and a fall in the IR-GH concentration following adrenocorticotropin administration. However, while the overall estimates of IR-GH concentration were significantly correlated, the magnitude of the changes in IR-GH concentration determined by the homologous assay were far greater than those detected by the heterologous system, which failed to show any inhibitory effect of anesthesia or exogenous thyroid hormones on basal or stimulated IR-GH release. These results suggest that the heterologous GH radioimmunoassay lacks the sensitivity of the homologous chicken GH assay and that circulating GH in birds is probably composed of heterogeneous moieties with differing immunoreactivities with rat GH antibodies.