A long-term effect of insulin on collagen synthesis by newborn rat bone in vitro

Disproportionate alterations in body composition of large for gestational age neonates

OBJECTIVE

The objective was to compare dual-energy x-ray absorptiometry-measured body composition between large (LGA) and appropriate (AGA) birth weight for gestational age neonates.

STUDY DESIGN

LGA term infants (n = 47) with birth weights > or =4000 g were compared with 47 gestational age-matched AGA infants; 11 LGA infants were born to mothers with gestational (9) or pregestational diabetes (2). Dual-energy x-ray absorptiometry scans were performed at 1.8 +/- 1.0 days after birth.

RESULTS

Body weight and length were the dominant predictors of body composition in LGA and AGA neonates. However, LGA neonates had significantly (P <.001, all comparisons) higher absolute amounts of total body fat, lean body mass, and bone mineral content and had significantly (P <.001, all comparisons) higher proportions of total body fat and bone mineral content but lower lean body mass as a percent of body weight. The changes for total body fat and lean body mass as a percent of body weight were greatest (P <.001) in LGA infants whose mothers had impaired glucose tolerance.

CONCLUSION

LGA neonates have higher body fat and lower lean body mass than AGA infants. Impaired maternal glucose tolerance exaggerated these body composition changes.

Effects of epidermal growth factor and transforming growth factor-beta on insulin-induced differentiation in rat dental pulp cells

An established pulp cell line (RPC-C2A) was used to study the regulatory effect of insulin on dentinogenesis. Insulin increased alkaline phosphatase activity and the incorporation of [2,3-3H]-proline into collagenase-digestible protein, whereas [3H]-thymidine incorporation by the cells was inhibited by insulin. The enhancing effect of insulin on alkaline phosphatase activity was inhibited by epidermal growth factor (EGF) or transforming growth factor-beta (TGF-beta). The stimulatory effect of insulin on collagen synthesis was also inhibited when insulin was combined with EGF, but was accelerated by the addition of TGF-beta. Inhibitory effects of insulin on the [3H]-thymidine incorporation were potentiated by EGF, though EGF alone strongly increased the effect; whereas the addition of TGF-beta had no significant effect on the insulin action. These findings suggest that insulin may be concerned with the differentiation of pulp cells in dentinogenesis and that EGF or TGF-beta regulate the insulin effects.

Effect of fibroblast growth factor on cultured fetal rat calvaria

Normal rat or human serum causes a greater incorporation of 3H-proline into bone collagenase digestible protein (CDP) and noncollagen protein (NCP) than does serum from hypophysectomized animals or hypopituitary humans. In the present study, we have tested fibroblast growth factor (FGF), a peptide isolated from bovine pituitary glands that has been shown to stimulate RNA and DNA synthesis in various mesodermal cells, for its effects on cultured fetal rat calvaria. The major effect of FGF appeared to be a stimulation of periosteal fibroblastic cell proliferation. Incorporation of 3H-thymidine into DNA was increased at concentrations of 10--1000 ng/ml; the effect appeared after 12 hr, was sustained for 96 hr, and could not be ascribed to an effect on 3H-thymidine uptake. Total DNA content was increased and histologic sections showed an increase in the number of mitoses in periosteal fibroblasts after colemid arrest. These effects were accompanied by an increase in the uptake and incorporation of 3H-uridine, a decrease in the incorporation of labeled proline into CDP, and a small and variable increase in the incorporation of proline into NCP. Cortisol opposed the effects of FGF on 3H-thymidine and 3H-uridine incorporation. Insulin did not alter the effect of FGF on 3H-thymidine incorporation, but FGF decreased the stimulatory effect of insulin on the labeling of CDP. The effect of FGF on thymidine incorporation and collagen synthesis was not altered by indomethacin. The major effect of FGF in calvaria is to increase DNA synthesis and stimulate the proliferation of periosteal fibroblasts. It does not appear to be the pituitary-dependent factor in serum that stimulates 3H-proline incorporation into CDP and NCP in calvaria.