The effects of thyroid hormone deprivation in vivo and in vitro on growth hormone (GH) responses to XXXX pancreatic (tumor) GH-releasing factor (1-40) by dispersed @entity35 anterior pituitary cells.

@entity1 @entity1375 @entity141 @entity1218 @entity3365 @entity35
Anterior pituitary cells from euthyroid and @entity1375 male @entity35 have been cultured as monolayers for 3 days with or without 5 nM T3 and stimulated with either @entity1 pancreatic GH-releasing factor 1-40 (hpGRF), @entity1218 , or the @entity141 channel ionophore @entity3365 . Basal GH secretion was reduced in the @entity1375 (P less than 0.001) and basal TSH secretion increased (P less than 0.001). Culture with T3 increased GH secretion and intracellular GH content in euthyroid and @entity1375 but suppressed TSH secretion with no effect on intracellular TSH content in either euthyroid or @entity1375 . hpGRF released more GH from euthyroid [3.52 +/- 0.2 (SE) micrograms/6 h X 10(5) cells] than @entity1375 of (0.17 +/- 0.01 micrograms/6 h X 10(5) cells, P less than 0.001) without a change in ED50 (approximately 0.02 nM). The reduction in hpGRF-induced GH release remained significant when corrected for the reduced intracellular GH content in the @entity1375 . hpGRF-induced GH release also declined relative to @entity3365 -induced GH release in @entity1375 . Culture with 5 nM T3 doubled maximum hpGRF-induced GH release in euthyroid cultures and increased maximum release 10-fold in @entity1375 without altering the ED50 of hpGRF action. In contrast, T3 suppressed @entity1218 -induced TSH release in euthyroid cultures but was without effect on @entity1218 -induced TSH release in the @entity1375 . T3 did not effect the ED50 of @entity1218 action (2-5 nM). In summary, @entity1375 @entity35 anterior pituitary cells in culture have a reduced maximal GH response to hpGRF, but the same ED50. hpGRF activity can be partially restored by physiological concentrations of T3 in vitro.
