Effects of hypothalamic hormones (GRF, TRH, somatostatin) and insulin-like growth factor I on growth hormone secretion from prepubertal male lamb pituitary cultures.
We have examined the regulation of GH secretion from monolayer cultures of prepubertal male lamb anterior pituitary cells. Growth hormone-releasing factor (GRF 1-44) stimulated GH release in a dose-related manner: the maximal effective dose was 10(-10) M, which caused a 500% increase in basal GH secretion, while the half-maximal effect was reached with a dose of 2.5 x 10(-11) M (ED50). Thyrotropin-releasing hormone (TRH) also elicited a dose-dependent stimulation of GH secretion, although it was approximately 1000 times less potent than GRF. GRF and TRH did not have additive or synergistic effects on GH secretion. Somatostatin (SRIF) at a concentration of 10(-7) M maximally inhibited basal GH release to 40% of that of the control; the ED50 was 2.0 x 10(-9) M. Moreover, 10(-7) M SRIF blocked the stimulation of GH secretion induced by 10(-8) M GRF. However, when the cells were incubated with these two peptides at an identical concentration (10(-8) M), GH secretion was stimulated significantly above control values. When added at the same concentration (10(-7) M, TRH ans SRIF nullified their respective effects. A dose of 100 ng/ml of synthetic IGF-I was without effect on basal GH release, but significantly decreased 10(-9) M GRF-induced stimulation of GH secretion. these data indicate that in prepubertal male lambs: the stimulatory effect of GRF is predominant over the inhibitory effect of SRIF, somatostatin inhibits TRH stimulation of GH secretion in vitro, and IGF-I may control GH secretion by modulating GRF effects at the pituitary level.
D000818:Animals; D002478:Cells, Cultured; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D007028:Hypothalamic Hormones / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D012741:Sexual Maturation; D012756:Sheep; D013004:Somatostatin / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D007028:Hypothalamic Hormones; D013004:Somatostatin; D013973:Thyrotropin-Releasing Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone