The lung parenchyma provides a maximal surface area of blood-containing capillaries that are in close contact with a large surface area of the air-containing alveoli. Volume and surface area of capillaries are the classic stereological parameters to characterize the alveolar capillary network (ACN) and have provided essential structure-function information of the lung. When loss (rarefaction) or gain (angiogenesis) of capillaries occurs, these parameters may not be sufficient to provide mechanistic insight. Therefore, it would be desirable to estimate the number of capillaries, as it contains more distinct and mechanistically oriented information. Here, we present a new stereological method to estimate the number of capillary loops in the ACN. One advantage of this method is that it is independent of the shape, size, or distribution of the capillaries. We used consecutive, 1 μm-thick sections from epoxy resin-embedded material as a physical disector. The Euler-Poincaré characteristic of capillary networks can be estimated by counting the easily recognizable topological constellations of "islands," "bridges," and "holes." The total number of capillary loops in the ACN can then be calculated from the Euler-Poincaré characteristic. With the use of the established estimator of alveolar number, it is possible to obtain the mean number of capillary loops per alveolus. In conclusion, estimation of alveolar capillaries by design-based stereology is an efficient and unbiased method to characterize the ACN and may be particularly useful for studies on emphysema, pulmonary hypertension, or lung development.

Intrauterine growth restriction (IUGR) is associated with foetal cardiac remodelling and dysfunction together with increased risk of cardiovascular disease in adulthood. Experimental data concerning effects of IUGR on cardiomyocyte and microvascularization anatomy are inconsistent and it is unknown whether both ventricles are similarly susceptible to in utero undersupply. Foetal IUGR was induced in pregnant rabbits at 25 days of gestation by selective ligation of uteroplacental vessels. Foetal echocardiography showed systolic and diastolic dysfunction of both ventricles and body and heart weight were significantly reduced in response to IUGR. Design-based stereology revealed a decrease in cardiomyocyte number in both ventricles which was only in the left ventricle accompanied by a significantly higher cardiomyocyte mean volume. The proportion of mono- and bi-nucleated cardiomyocytes was unaltered between the groups indicating a similar maturation status. The number and length of cardiac capillaries in IUGR offspring was diminished in left but not in right ventricles. Foetal left and right ventricles are differently affected by placental insufficiency. While cardiomyocyte numbers are diminished in both ventricles, hypertrophic remodelling of cardiomyocytes and alterations in microvascularization is rather a left ventricular adaptation to IUGR. These unequal structural changes may be related to loading and developmental differences of the left and right ventricles.