Impaired Response of Serum IGF-I Levels to Puberty in Previously Malnourished Adolescents.

Serum levels of IGF-I were measured in Barbadian children, aged 9-15 years, half of whom had experienced protein-energy malnutrition limited to the first year of life. Despite current nutritional adequacy, menarche was delayed more than one year in the girls with a history of early malnutrition and their IGF-I levels failed to show the 60% postmenarchic increase seen in the controls. In addition, the IGF-I levels of boys and girls with prior malnutrition in infancy were not significantly correlated with current anthropometric measurements, whereas IGF-I values of control boys and girls were significantly correlated for almost every growth parameter.

Degradation of porcine relaxin by glutathione-insulin transhydrogenase and a neutral peptidase.

The susceptibility of porcine relaxin and 125I-polytyrosyl-porcine relaxin to degradation by 3 purified enzymes involved in the degradation of insulin and proinsulin was examined. Rat liver glutathione-insulin transhydrogenase (GIT), which cleaves disulfide bonds in insulin, catalyzed a time- and concentration-dependent increase in trichloroacetic acid (TCA)-soluble radioactivity of relaxin. The Sephadex G-50 profile of the reaction products revealed conversion to the A- and B-chains.

Placental lactogen administration reverses the effect of low-protein diet on maternal and fetal serum somatomedin levels in the pregnant rat.

Female rats were studied on day 20 of pregnancy after being fed either a 5% lactalbumin (low protein) diet or a 20% lactalbumin (adequate) diet for the last 2 weeks of pregnancy. Rats on the lower intake of protein showed decreased serum levels of rat placental lactogen and reduced numbers of lactogenic receptors in the maternal liver. These changes were accompanied by much reduced serum levels of somatomedins IGF I(insulin-like growth factor) and II (multiplication-stimulating activity, MSA).

Insulin-like growth factor receptors in rat placental membranes.

The nature and relative quantity of insulin-like growth factor (IGF) receptors in rat placental microsomal membranes was investigated by competitive binding studies and covalent cross-linking followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Binding studies revealed that 100 micrograms membrane protein specifically bound 26.5% of [125I]iodo-IGF-II, 19.

Protein deficiency in pregnant rats causes decreased levels of plasma somatomedin and its carrier protein associated with reduced plasma levels of placental lactogen and hepatic lactogenic receptor number.

Rats were fed either a 20% lactalbumin (control) or a 5% lactalbumin (low protein) diet for the last 2 weeks of pregnancy. At day 20 of gestation, rat serum placental lactogen levels, measured by radioreceptor assay, were significantly decreased by the low protein diet, thus confirming our earlier findings. The number of microsomal membrane lactogenic receptors, measured on the maternal livers at the end of pregnancy, was severely reduced in the livers of the low protein group, whereas protein deficiency did not affect binding affinity.