Thyroid hormones are required for the normal development of skeletal muscle in utero, although their mechanism of action is poorly understood. The present study examined the effects of the thyroid hormones on the gene expression of the @entity43872 ( @entity43872 ) and the insulin-like growth factors (IGFs) @entity9418 and @entity9419 , in skeletal muscle of fetal @entity742 during late gestation (term 145 +/- 2 days) and after manipulation of plasma thyroid hormone concentration. Thyroidectomy at 105-110 days of gestation suppressed muscle @entity43872 and @entity9418 gene expression in fetuses studied at 127-130 and 142-145 days. Muscle @entity43872 mRNA abundance remained unchanged with increasing gestational age in intact and thyroidectomized fetuses. In the intact fetuses, a decrease in muscle @entity9418 gene expression was observed between 127-130 and 142-145 days, which coincided with the normal prepartum surges in plasma @entity701 and @entity1954 (T3). At 127-130 days, downregulation of muscle @entity9418 mRNA abundance was induced prematurely in intact fetuses by an infusion of @entity701 for 5 days (2-3 mg x kg(-1) x day(-1) iv), which increased plasma @entity701 and T3 concentrations to values seen near term. However, increasing plasma T3 alone by an infusion of T3 for 5 days (8-12 microg x kg(-1) x day(-1) iv) in intact fetuses at this age had no effect on @entity43872 or @entity9418 gene expression in skeletal muscle. In the thyroidectomized fetuses, no additional change in the low level of muscle @entity9418 mRNA abundance was seen with increasing gestational age, but at 127-130 days, @entity9418 gene expression was reduced further when plasma @entity701 and T3 concentrations were increased by exogenous @entity701 infusion. Muscle @entity9419 mRNA abundance was not affected by thyroidectomy, gestational age, or exogenous hormone infusion. These findings show, in the @entity742 fetus, that thyroid hormones may influence the growth and development of skeletal muscle via changes in the local activity of the @entity10759 .

Thyroid hormones and the mRNA of the @entity43872 and IGFs in skeletal muscle of fetal XXXX .

@entity43872 :: ('443333(Tax:9940)', 'Gene') :: ['GHR', 'growth hormone receptor'] @entity742 :: ('9940', 'Species') :: ['sheep'] @entity9419 :: ('443325(Tax:9940)', 'Gene') :: ['IGF-II'] @entity9418 :: ('443318(Tax:9940)', 'Gene') :: ['IGF-I'] @entity701 :: ('MESH:D006854', 'Chemical') :: ['cortisol'] @entity10759 :: ('MESH:D049912', 'Disease') :: ['somatotrophic axis'] @entity1954 :: ('MESH:D014284', 'Chemical') :: ['triiodothyronine']
@entity742 :: (9940,Species) :: ['sheep']
