Reduction of insulin-like growth factor-I (IGF-I) in protein-restricted rats is associated with differential regulation of IGF-binding protein messenger ribonucleic acids in liver and kidney, and peptides in liver and serum.

To investigate the influence of the insulin-like growth factor binding-proteins (IGFBPs) on the nutritional regulation of IGF-I's actions, we compared the gene expression of IGF-I and the six IGFBPs in liver and kidney of protein-restricted (P5) and normally fed (P15) young rats. Using poly(A)+ Northern blot analysis, we observed a decrease in IGF-I messenger RNA (mRNA) at steady state in liver (-50%) and kidney (-60%). The increases in IGFBP-1 mRNA were parallel in these two tissues (liver, 5.7-fold; kidney, 4-fold). In contrast, the expression of the other IGFBP genes exhibited organ-specific regulation during protein restriction; although IGFBP-2 mRNA increased in liver in the P5 group (3-fold), it decreased slightly in kidney (-15%). IGFBP-3 mRNA declined by 30% in liver and was unchanged in kidney. IGFBP-4 mRNA increased by 50-88% in liver and was not modified in kidney. IGFBP-5 mRNA was not detected in liver and was identical in kidney of P15 and P5 rats. IGFBP-6 mRNA was not changed in either liver or kidney during protein restriction. To determine whether the changes in IGFBP mRNAs induced by protein restriction were associated with changes in the respective peptides, IGFBPs in supernatants of liver homogenates and in serum of the same rats were measured by ligand blot analyses. IGFBP-1 and IGFBP-2 Western immunoblot analyses were also performed in serum. By ligand blot, a 45,000 mol wt (M(r)) band (IGFBP-3) decreased in liver and serum of P5 rats, paralleling the changes in liver IGFBP-3 mRNA. A 30,000 M(r) band, consistent with IGFBP-1 and/or IGFBP-2, increased in liver. By immunoblot in serum, IGFBP-1 was only detectable in P5 rats, whereas IGFBP-2 decreased in the P5 group. By ligand blot, a 24,000 M(r) band (IGFBP-4) declined slightly in serum (not detected in liver). Our study shows that protein restriction regulates the expression of four of six IGFBPs in rats, and this regulation is organ specific. The nutritional regulation of IGFBP peptides in biological fluids, in particular serum, seems to involve additional mechanisms.

Hormonal and nutritional regulation of IGF-I and its binding proteins.

The influence of nutrition on growth seems likely to be mediated in part through IGF-I. Restriction of dietary nutrients adversely effects IGF-I synthesis and action at multiple steps, including decreased GH receptors, postreceptor defects in GH action, decreased steady state levels of IGF-I mRNA, and attenuation of IGF-I action. In addition, undernutrition affects the IGF binding proteins in ways that vary from one tissue to another. Understanding the alterations in IGFBPs that are caused by nutritional insufficiency may provide insight into the actions of the IGFBPs.

Effect of blood flow on thrombin generation is dependent on the nature of the thrombogenic surface.

We have investigated the influence of blood flow on thrombin generation, fibrin formation, and fibrin deposition on procoagulant and nonprocoagulant surfaces. Nonanticoagulated human blood was drawn for 5 minutes directly from an antecubital vein over stimulated endothelial cells expressing tissue factor and over human type III collagen fibrils, positioned in parallel-plate perfusion chambers. The shear rates at these surfaces were 50, 650, and 2,600 s-1. Deposition of platelets and fibrin was measured by morphometry. Thrombin and fibrin formation was determined by measuring prothrombin fragments 1 + 2 (F 1 + 2), thrombin-antithrombin III complexes, (T-AT) and fibrinopeptide A (FPA) in blood effluent from the perfusion chamber at the end of the 5-minute perfusion period. On procoagulant endothelial cells, the thrombi were primarily composed of fibrin. The fibrin deposition (81%, 21%, and 2% at 50, 650, and 2,600 s-1, respectively) and plasma levels of F 1 + 2, T-AT and FPA were shear rate dependent and highest at 50 s-1. There was a positive correlation between F 1 + 2 and T-AT and the fibrin deposition (P < .01). In contrast, the collagen surface triggered primarily thrombi that were composed of platelets. The platelet thrombi and plasma levels of F 1 + 2 and T-AT were also dependent on the shear rate, but highest at 650 and 2,600 s-1. F 1 + 2 and T-AT reached the same level as observed with procoagulant endothelial cells at the higher shear rates. There was a positive correlation between F 1 + 2 and T-AT and the platelet thrombus formation (P < .05), confirming the predominant role of platelets in thrombin generation. Thus, thrombin formation is strongly influenced by the blood flow, and this effect depends on the composition of the thrombogenic surface.

Human type II hyperlipoproteinemia enhances platelet-collagen adhesion in flowing nonanticoagulated blood.

We investigated the effects of high plasma lipid levels on platelet adhesion and platelet thrombus formation in nonanticoagulated human blood on collagen fibrils at an arterial wall shear rate of 2600 seconds-1. Nonanticoagulated blood was drawn directly at a flow rate of 10 mL/min for 3 minutes from an antecubital vein of patients with type IIa (n = 5) and type IIb (n = 4) hyperlipoproteinemia over purified human type III collagen fibrils that were positioned on a plastic coverslip in a parallel-plate perfusion chamber. Results were compared with those obtained in healthy individuals with normal lipid plasma levels (n = 9). Blood-collagen interactions were quantified by morphometry as platelet-collagen adhesion, thrombus volume, and fibrin deposition. Platelet-collagen adhesion in the two groups of patients was significantly higher than in healthy individuals (70.7 [61.2 to 82.0] and 70.3 [66.4 to 81.0] in types IIa and IIb patients, respectively, versus 51.2 [44.5 to 68.6] in control subjects; P < .05. All values are percent median [range]). In contrast, the thrombus volume was similar in the three groups (11.3 [8.0 to 13.0], 9.6 [6.4 to 15.3], and 10.2 [6.8 to 16.1] microns3/microns2 [range], respectively). Differences in fibrin deposition were not observed. Thus, it appears that platelet-collagen adhesion is augmented in patients with type IIa and IIb hyperlipoproteinemia, indicating that the process of thrombogenesis is hastened in these patients.