Stimulation by food of peripheral plasma immunoreactive growth hormone releasing factor

A highly specific radioimmunoassay has been used to study changes in peripheral human plasma growth hormone releasing factor (GRF) following the ingestion of food. From a mean basal plasma concentration of 11.8 pg/ml (range less than 7-15.4 pg/ml) in six normal individuals following overnight fast, the circulating concentration of GRF-like immunoreactivity increased to a mean maximum of 36.7 pg/ml (range 20.2-77.0 pg/ml) sampled 120 min after a mixed breakfast. This increase in GRF was accompanied by suppression rather than stimulation of circulating growth hormone. The predominant source of peripheral circulating GRF-like immunoreactivity may therefore by extrahypothalamic and responds to an oral food stimulus.