Stimulation and inhibition of pituitary growth hormone release by angiotensin II in vitro

Rat pituitary cell aggregates cultured in serum-free chemically defined medium, single cells, and hemipituitaries were used in a perifusion system to study the influence of angiotensin II (AII) on GH release. In aggregates the peptide displayed both stimulatory and inhibitory effects on GH release, depending on the hormonal conditions of the culture medium and the age of the animal. When cultured in the absence of glucocorticoid, a modest but statistically significant stimulation was seen in aggregates from immature as well as adult animals. In aggregates from 5-day-old animals, dexamethasone (DEX) strongly enhanced the GH-releasing activity of AII in a dose-dependent way; in aggregates from 14- and 25-day-old rats, the same pattern was found, although the stimulatory action was weaker than the effect in 5-day-old rats. In aggregates from adult animals, the glucocorticoid established an inhibitory effect of AII on GH release, an effect seen with both low and high concentrations of DEX. These age- and DEX-dependent effects were not found for AII stimulation of PRL release. In the presence of DEX, AII also inhibited GRF-induced GH release in aggregates from adult animals, while it was synergistic with GRF in aggregates from developing animals. The effects of AII on GH release disappeared when aggregates were redispersed into single cells. However, in these single cell preparations AII strongly stimulated PRL release. In hemipituitaries from 1-, 5-, and 14-day-old animals, AII also stimulated GH release, but no effect was seen in hemipituitaries from 25-day-old and adult animals. These data indicate that AII has dual effects on GH release depending on the developmental stage of the animal and the hormonal environment. Furthermore, since no effect of AII was seen after redispersion of aggregates into single cells, both stimulatory and inhibitory effects seem to be based on an intercellular signaling system.