GH3 cell secretion of growth hormone and prolactin increases spontaneously during perifusion

GH3 cell secretory activity was studied in long-term perifusion to define previously reported spontaneous increases in growth hormone (GH) and prolactin production (PRL). Mechanically harvested cells (1 X 10(7)/column) were perifused at 4 ml/h for 72 h. A basal period of variable duration (8 to 12 h), during which hormone secretion was stable, was followed by steadily increasing secretion rates. Changes in cell number were not sufficient to account for increased hormone secretion rates: a) there was no significant change in cell count after 72 h (0.97 +/- 0.03 X 10(7); n = 18); b) mean cell column DNA content increased 25.5% above the base value, whereas GH secretion rose 385% and PRL rose 178% (n = 5). Observed differences in the duration of the basal secretion period, the basal secretory rate, and the magnitude of secretory rate increase were associated with several variables: a) variability within a subline was a function of passage number: GH secretion decreased and PRL secretion increased with subculture number; b) cells with identical lot and freeze numbers, but received at different times, behaved differently; c) the presence of an antifungal agent (nystatin) altered hormone secretion reproducibly.

a) rates of GH and PRL secretion rise spontaneously in perifusion without a proportional increase in GH3 cell number; b) fluctuations in the rate of GH3 cell secretion of GH and PRL are not entirely random but are determined by several definable variables.