Effect of cell density on growth hormone release from, cyclic AMP levels in and peptide α-amidation activity of primary cultured rat anterior pituitary cells

To investigate the effect of cell density on rat somatotrophs, dispersed adult rat anterior pituitary cells were plated at several densities (0.6, 1.2, 2.4 and 6.0 x 10(5) cells/cm2) or at two densities (6.07 x 10(5) and 1.21 x 10(5) cells/cm2) as high and low densities respectively. A static incubation system was used to study the release of GH and peptidyl glycine alpha-amidating enzyme (PAM; a component of secretory granules) and the cellular concentration of cyclic AMP (cAMP) in basal and stimulated cells. In addition, a perifusion system was used to characterize the sensitivity to GH-releasing factor (GRF) at both high and low densities. The high density of cells in both the static incubation and perifusion systems caused a low basal secretion rate of GH and PAM. When the cultured cells were stimulated with human GRF (hGRF) in perifusion, GH secretion from cells at high density was markedly higher than that from cells at low density. The cAMP content in the static incubation system showed a similar tendency to that observed for basal and stimulated GH secretion; that is, the basal cAMP content was increased as the cell density decreased. The cellular concentration of cAMP was increased by about threefold by 1 nmol hGFR/l and by more than tenfold by 10 nmol hGRF/l. When the medium from cells cultured at low density was replaced by that from the cells at high density, there was no change in the basal cellular cAMP content of the cells at low density.(ABSTRACT TRUNCATED AT 250 WORDS)