Role of Locally Produced Growth Hormone-Releasing Factor in Somatostatin Regulation by Fetal Rat Brain Cells in Culture

To determine the possible physiological role of endogenous growth hormone-releasing factor (GRF) in the neuronal content and release of cerebral somatostatin (SS), we studied the effect of endogenous GRF blockade on the immunoreactive SS (IR-SS) content of cells and media in fetal rat cerebral cortical and hypothalamic cells in culture. Cells were cultured in minimum essential medium (MEM) with 10% fetal calf serum and 10% horse serum. After 7–10 days in vitro, media were replaced with MEM without sera containing anti-GRF immunoglobulins G (IgG) for 1, 5 or 24 h. Controls were incubated with equal amounts of IgG from normal rabbit serum (NRS). In another group of experiments, cells were incubated with GRF (10–11 to 10–7M) for 1 or 24 h. Long-term exposure (24 h) to anti-GRF IgG resulted in decreased media and intracellular IR-SS content, in both cerebral cortical and hypothalamic cells. 24 h treatment with GRF caused a dose-dependent increase in the IR-SS content of cells and media, the stimulatory action being abolished by the addition of anti-GRF to plates containing 10–7M GRF. On the contrary, when cells were exposed to anti-GRF IgG for 1 h, IR-SS increased in the media as compared to the control group. Short-term incubation (1 h) with GRF (10–9 to 10–7M) resulted in a dose-dependent inhibition of IR-SS content in the cells and media. This inhibitory action was partially prevented by the addition of anti-GRF to plates containing 10–7M GRF. Patterns of IR-SS cell and media content were qualitatively similar in both cerebral cortical and hypothalamic cells. In plates containing anti-GRF, the accumulation of IR-SS in the cells and media was lower than in the control groups (IgG from NRS) throughout the incubation time.