Growth Hormone Secretion by Cultured Rat Anterior Pituitary Cells. Effects of Culture Conditions and Dexamethasone*

Abstract

Optimal conditions were sought for the study of GH [growth hormone] secretion by cultured normal pituitary cells. Dispersed rat pituitary cells were cultured for 1 wk in 4 different media supplemented with 10% fetal calf serum. Minimal essential medium resulted in high GH content and secretion during a 4-h incubation period, while GH secretion was lower (P < 0.05) for cells cultured in medium 199, Ham''s F-10 and RPMI-1640. GH secretion/24 h declined gradually with time. After 2 wk in culture hormone secretion amounted to 30% of secretion on day 1, but after 3 wk GH secretion was still measurable. GH recovery during the 3-wk culture period was more than 600% of the amount initially plated. GH secretion was positively correlated with the bicarbonate concentration between 0.85 and 2.2 g/l NaHCO3. When pituitary cells were cultured in concentrations varying from 0.5 .times. 105 to 10 .times. 105 cells per fish, GH secretion and content per cell were constant, suggesting that no direct autofeedback occurred in cultures with high cell densities and high medium GH. Dexamethasone stimulated GH secretion and content in a dose-dependent way (0.1 nM-10 .mu.M). The stimulatory effect of 100 nM dexamethasone occurred within 24-48 h. After 7 days of treatment with 100 nM dexamethasone, GH secretion had increased to 190% and GH contents to 230% of control. In contrast to the effects on GH, dexamethasone suppressed PRL [prolactin] secretion in a dose-dependent way, but this effect was seen only after 7 days of treatment and not after 4 days of treatment. Cycloheximide and actinomycin D prevented the stimulatory effect of dexamethasone on GH secretion. However, 24 h after cessation of cycloheximide treatment GH secretion was stimulated by dexamethasone. Four days of treatment with 100 nM dexamethasone did not affect the GH response to somatostatin, prostaglandin E1 and theophylline, nor the PRL response to dopamine. TRH and theophylline. Culture conditions may affect GH production, and dexamethasone can be used to culture somatotrophs for longer periods with steady GH production and normal responsiveness.