Modulation of growth hormone-releasing factor-induced release of growth hormone from bovine pituitary cells.

Growth hormone (GH)-releasing factor (GRF) at concentrations of 10(-12) through 10(-7) M for 6 hr linearly increased GH release (b1 = 10.4 +/- .3) from bovine anterior pituitary cells in culture. Maximum release of GH (262% above controls) occurred at 10(-7) M GRF. In contrast, GH release-inhibiting factor (SRIF) at 10(-12) through 10(-5) M had no effect on basal concentrations of GH. In a second experiment, as the proportion of SRIF relative to GRF increased, SRIF suppression of GRF-induced GH release from anterior pituitary cells increased. In a third experiment, anterior pituitary cells cultured in media containing fetal calf serum (FCS) were treated with cortisol (0 or 10 ng/ml media) for 24 hr before exposure to 10(-13) through 10(-7) M GRF. GRF linearly increased GH secretion (b1 = 7.4 +/- .3) and cortisol augmented this response (b1 = 10.5 +/- .6). However, when cells were cultured in media containing dextran-charcoal treated FCS, cortisol did not alter GRF-induced GH release. Our results demonstrate that GH response of bovine anterior pituitary cells to GRF was modulated negatively by SRIF. However, augmentation of GRF-induced GH release by cortisol was evident only when cells were cultured in media supplemented with untreated FCS.