Increased levels of multiplication-stimulating activity, an insulin-like growth factor, in fetal rat serum.

Abstract

Multiplication-stimulating activity (MSA), purified from medium conditioned by the BRL-3A rat liver cell line, previously has been shown to be closely related to the human somatomedins or insulin-like growth factors. A radioimmunoassay was utilized to measure MSA levels in sera from fetal, maternal, and young rats. A serum somatomedin-binding protein was found to interfere in the radioimmunoassay by competing with antibody for binding 125-Ilabeled MSA. Therefore, prior to radioimmunoassay, sera were filtered on Sephadex G-75 in 1 M acetic acid to dissociate and separate somatomedin activity from the binding protein. Concentrations of MSA by radioimmunoassay were 20-to 100-fold higher in fetal rat sera (1.8-4.4 pg/ml) than in maternal sera. MSA levels gradually decreased after birth, reaching maternal levels by day 25 of extrauterine life. MSA concentrations in fetal rat sera also were found to be correspondingly high by a rat liver membrane radioreceptor assay and a competitive binding protein assay using rat serum somatomedin-inding protein. The findings of higher levels of MSA in fetal than in maternal rat sera and the gradual decline in MSA serum concentrations after birth are in

Parathyroid hormone increases the concentration of insulin-like growth factor-I and transforming growth factor beta 1 in rat bone.

“…The matrix concentrations of IGF-ll in the vehicle-treated animals did not significantly change with time either. There was a remarkable 60% decline in circulating IGF-II during the course of the experiment (P = 0.0001, ANOVA), indicating that the decline in serum IGF-II that can be observed in rats within a few days after birth (21,22), continues into early adulthood (Fig. 4 B).…”

Insulin-like growth factor II (IGF-II) mRNA expression during skeletal muscle development of double-muscled and normal bovine foetuses

“…Expression of the insulin-like growth factor-II (IGF-11) gene is greater during foetal development than at any other period in the life of mammals [29,30,40]. Moreover, the disruption of this gene greatly diminishes prenatal growth in mice [6].…”

Lack of effect of exogenous insulin-like growth factor-I (IGF-I) on chick embryo growth rate

“…IGF-I blood levels are low in fetal life compared to postnatal values (Gluckman et al, 1983;Spencer GSG et al, 1983); in contrast, IGF-11 levels were found to be high in the fetus of some species (Moses et al, 1980). However, a direct study of the effect of IGF-11 on fetal growth has failed to show any positive effect on the growth of pig fetuses (Spencer, 1986).…”

“…Thigh muscle was removed, weighed and frozen in liquid nitrogen and stored at -20 °C for later measurement of DNA, RNA and protein content (Wannemacher et al, 1965;Munro and Fleck, 1966;Abraham et al, 1972 Ashton and Francis, 1978;Weidman and Bala, 1980) and the ability of tissues such as chick liver cells (Haselbacher et al, 1980) and chick cartilage (Burch et al, 1986), to synthesize IGF-I (d'Ercole et al, 1976), it is widely believed that IGF-11 may be the somatomedin involved in growth promotion in the fetus (Moses et al, 1980). IGF-I blood levels are low in fetal life compared to postnatal values (Gluckman et al, 1983;Spencer GSG et al, 1983); in contrast, IGF-11 levels were found to be high in the fetus of some species (Moses et al, 1980).…”