AJP - Endocrinology and Metabolism, Vol 268, Issue 2 E262-E267, Copyright © 1995 by American Physiological Society
Regulation of growth hormone expression in fetal rat pituitary gland by thyroid or glucocorticoid hormone
H. Nogami, T. Yokose and T. Tachibana
Department of Anatomy, Jikei University School of Medicine, Tokyo, Japan.
The regulation of growth hormone (GH) cell development by thyroid and
glucocorticoid hormones in the fetal rat pituitary gland was examined.
Dexamethasone (Dex) treatment of dams induced GH and GH mRNA accumulation
in the fetal pituitary gland on day 17 or 18 of gestation when substantial
GH expression has not yet occurred in the control fetus. The additional
thyroxine injections apparently enhanced the effect of Dex, whereas it
exhibited no effect when given alone. The reduction of fetal thyroid
hormone level by methimazole suppressed either the Dex induction of GH
expression on day 18 or the spontaneous onset of GH expression on day 19 of
gestation. The results suggest that 1) thyroid hormone exerts its
stimulatory action on fetal GH gene expression only in the presence of
glucocorticoid, 2) this synergistic action of these two hormones is evident
as early as day 17 of gestation, and 3) rapid maturation of GH cells seen
on day 19 in the normal fetus is considered to be induced by concomitant
increase in both serum thyroid and glucocorticoid hormone levels.
