The influence of GH and several other pituitary hormones on the secretion and intracellular content of immunoreactive somatostatin (IRS) in cultured hypothalamic cells was examined. Hypothalamic cells prepared from 17-day-old rat embryos and maintained as reaggregate monolayers for 12 days in vitro were used. Short term release of IRS from these cultures was found to be stable and relatively constant. IRS release was enhanced by 60 mM K+ in a calcium-dependent fashion and by dopamine at concentrations as low as 1 nM. GH (1 μM) increased medium IRS content above baseline 12, 24, and 48 h after the incubation was begun, but had no effect after only 4 h. Hypothalamic cell content of IRS was increased by a 24-h incubation in 0.3 and 1.0 μM GH, but not by 0.1 μM GH. TSH (1 μM) induced an increase in IRS release comparable to 1 μM GH. However, intracellular IRS content was decreased after exposure to TSH. Cosyntropin, an ACTH analog, inhibited both IRS release and cell content, whereas PRL had no effect on either medium or cellular IRS content. Our results demonstrate that developing somatostatinergic neurons in the hypothalamus have the capacity to respond to pituitary hormones, indicating that short-loop feedback pathways may exist in perinatal hypothalamic cells.
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