Quantitative study of intussusceptive capillary growth in the chorioallantoic membrane (CAM) of the chicken embryo.

In an attempt to sort out the respective contributions of sprouting and intussusceptive microvascular growth (IMG) during chicken chorioallantoic membrane (CAM) development, we analyzed the morphology and the quantitative growth of the capillary bed of the CAM by light microscopy. By perfusing the CAM microvasculature with highly concentrated colloidal gold particles, the capillaries could be unambiguously distinguished from the surrounding unlabelled tissue. This allowed us to identify, count and measure the intercapillary tissue profiles. By means of morphometric analysis we could show that CAM angiogenesis undergoes three phases of development. In an early phase, from Day 5 to Day 7, the major mechanism of capillary network growth is sprouting. In an intermediate phase, from Day 8 to Day 12, IMG is prevailing, and at Days 13 and 14, CAM structure is undergoing expansion with only a small increase in complexity. These findings are important in view of experimental protocols using the CAM as a model for testing angiogenetic factors. Indeed, care has to be taken not to misinterpret normal age-dependent alterations of the CAM vascular architecture as specific responses to tested agents.

Relationship between body fat and anthropometric variables in a large sample of young males.

To establish the relationship between fat mass (FM) and other anthropometric variables, 2152 males of mid-European extract aged between 18 and 24 years were examined. Based on these data, three models for either fat percent (FP) or FM prediction were calculated from body mass (BM), body height (BH) and body mass index (BMI = BM/BH2). The best models for fat percent prediction both explained only 51% of the variance (FP = 0.02711.BMI2.042 (0.043 SE); and FP = 720310.BM2.05 (0.043).BH-3.76 (0.155), R2 = 0.51 for both models). There was a remarkable increase in R2 when FP was replaced by FM. The best model explained 70% of the variance for FM prediction (FM = 7207.BM3.05 (0.043).BH-3.76 (0.155), R2 = 0.70). We have incorporated these data into a nomogram applicable to an active, young male mid-European population. From this study we conclude that for the estimation of body fat, models based upon FM (absolute value) are preferred over models for prediction of FP (relative value).

Demonstration of pulmonary vascular perfusion by electron and light microscopy.

To estimate the fraction of dense pulmonary capillary network that is perfused under physiological conditions, we developed a new method for the demonstration of in vivo capillary perfusion by light and electron microscopy. Blood plasma was labeled by 8-nm colloidal gold particles coated with rabbit serum albumin. In anesthetized rabbits, 4-5 ml of this tracer were injected into the right atrium. Two and 15 min later, the circulation was interrupted by a snare around the heart, and the lung was fixed by instillation with glutaraldehyde. Gold particles were found in the plasma space of alveolar capillaries as well as in other organs. A random sample of thin sections studied by electron microscopy revealed that the entire capillary bed of the lung was perfused at least with plasma within 2 min after tracer infusion. Light microscopy of silver-enhanced sections showed areas with different staining intensities but no obviously unperfused capillaries. The concept of capillary recruitment, which would require a significant fraction of capillaries unperfused at rest, may have to be reassessed to consider time factors as well as the two-phase nature of blood; red blood cells and plasma may take different paths.