The effects of thyroid hormones on @entity99 factor (IGF) II gene expression and their interaction with @entity701 in the ontogenic control of this gene were investigated in fetal @entity742 during late gestation (term 145 +/- 2 days) and after experimental manipulation of fetal plasma hormone concentrations. In intact fetuses, a significant decrease in hepatic @entity9419 mRNA abundance was observed between 127-130 and 142-145 days of gestation, which coincided with the normal prepartum rise in plasma @entity701 and @entity1954 (T3) concentrations. This ontogenic decline in hepatic @entity9419 gene expression was abolished in fetuses in which the prepartum rise in plasma T3, but not @entity701 , was prevented by fetal thyroidectomy. At 127-130 days, downregulation of hepatic @entity9419 mRNA abundance was induced prematurely in intact fetuses by an infusion of @entity701 for 5 days (2-3 mg . kg-1 . day-1 iv). Plasma concentrations of @entity701 and T3 in the @entity701 -infused intact fetuses were increased to values seen close to term. Similar findings were observed in thyroidectomized fetuses, in which, despite thyroidectomy, @entity701 infusion significantly increased plasma T3 concentrations and caused a premature decrease in hepatic @entity9419 mRNA levels. However, in intact fetuses at 127-130 days, the increasing of T3 concentrations alone by exogenous T3 infusion (8-12 microg . kg-1 . day-1 iv for 5 days) had no effect on hepatic @entity9419 mRNA levels. Overall, a decrease in hepatic @entity9419 mRNA abundance was only observed in fetuses in which there were concurrent increases in plasma @entity701 and T3 concentrations. When observations from all fetuses were considered, irrespective of gestational age or treatment, hepatic @entity9419 mRNA levels were negatively correlated with plasma @entity701 and T3 but not @entity1955 concentrations. Partial correlation analysis of hepatic @entity9419 , @entity701 , and T3 values showed that the plasma concentration of @entity701 in the fetus had the predominant effect on hepatic @entity9419 mRNA abundance. These findings show that T3 may mediate, in part, the maturational effects of @entity701 on hepatic @entity9419 gene expression but that it is ineffective without a concomitant rise in fetal plasma @entity701 . Hence, increased concentrations of both @entity701 and T3 appear necessary to induce downregulation of hepatic @entity9419 mRNA abundance in fetal @entity742 close to term.

Control of @entity99 factor II gene expression by thyroid hormones in fetal XXXX near term.

@entity742 :: ('9940', 'Species') :: ['sheep'] @entity9419 :: ('443325(Tax:9940)', 'Gene') :: ['IGF-II'] @entity1955 :: ('MESH:D013974', 'Chemical') :: ['thyroxine'] @entity701 :: ('MESH:D006854', 'Chemical') :: ['cortisol'] @entity99 :: ('MESH:D056486', 'Disease') :: ['hepatic insulin-like growth'] @entity1954 :: ('MESH:D014284', 'Chemical') :: ['triiodothyronine']
@entity742 :: (9940,Species) :: ['sheep']
