Retinoic Acid Selectively Stimulates Growth Hormone Secretion and Messenger Ribonucleic Acid Levels in Rat Pituitary Cells*

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Abstract
Hydrocortisone (HCT) is known to stimulate rat GH gene expression. As the retinoic acid receptor cDNA bears a 15% homology to the hydrocortisone receptor cDNA, the effects of retinoic acid were tested in GH3 rat pituitary cells. Retinoic acid selectively stimulated GH secretion after 24 h. Maximal induction of basal GH secretion (220% of controls) was achieved with 1 μM retinoic acid after 72 h. HCT (50 nM) alone stimulated GH secretion 3.5-fold during 72-h incubation, and retinoic acid (1 μM) with HCT caused a further 7-fold increase in GH secretion. The stimulating effects of retinoic acid on GH were observed when cells were incubated in defined serum-free medium, 4% fetal calf serum, or Dulbecco's Modified Eagle's Medium containing HCT. Northern gel hybridization showed that steady state levels of GH mRNA transcripts in these cells were also selectively induced by retinoic acid. PRL secretion and mRNA levels, however, were not appreciably altered by retinoic acid. The results show that retinoic acid selectively stimulates basal and HCT-induced GH secretion and mRNA levels in these cells in a dose- and time-dependent manner. This selective action of retinoic acid appears to occur independently of the presence of serum in the culture medium. (Endocrinology124: 2052-2056,1989)