Triiodothyronine (T3) inhibition of growth hormone secretion by chicken pituitary cells in vitro

Abstract These studies examined the cellular basis for the inhibitory effects of triiodothyronine (T 3 ) on growth hormone-releasing factor (GRF)-evoked growth hormone (GH) release from chicken anterior pituitary cells in vitro . A primary monolayer culture of anterior pituitaries from 4- to 8-week-old White Leghorn cockerels was performed as previously described by this laboratory. Following a 72-hr preincubation period, cells were washed and incubated (2 hr) with either secretagogues or media alone (control). T 3 (20 ng/ml) or vehicle was added to cells during both the preincubation (48–72 hr) and incubation (2 hr) period. Triiodothyronine reduced ( P P 3 -treated versus non-T 3 -treated cells. These data indicate that T 3 inhibits GRF-evoked GH release by reducing the availability of intracellular stores of GH and by also inhibiting second messenger-stimulated GH release pathways.