H. Sugihara et al., Effect of insulin-like growth factor-I on growth hormone-releasing factor receptor expression in primary rat anterior pituitary cell culture, NEUROSCI L, 276(2), 1999, pp. 87-90
We examined the effect of insulin-like growth factor-I (IGF-I) on GH-releas
ing factor (GRF) receptor expression in the primary rat anterior pituitary
cell culture. The levels of GRF receptor mRNA were dose-dependently reduced
by IGF-I treatment for 24 h. To clarify whether altered levels of GRF rece
ptor mRNA contribute to GRF receptor concentrations, we examined the GH res
ponse to GRF in vitro. There was no difference in basal GH secretion betwee
n control and IGF-I pretreated cells, while GRF-stimulated GH secretion in
cells pretreated with IGF-I for 24 h was significantly lower than that in c
ontrol cells. Moreover, specific [I-125] Tyr(10)-human GRF binding to pitui
tary cells was reduced significantly by IGF-I treatment. These results sugg
est that IGF-I acts directly on the pituitary a nd participates in the regu
lation of GRF receptor expression. (C) 1999 Elsevier Science Ireland Ltd. A
ll rights reserved.