Evolution of the microvascular distensibility during the embryo growth. Example of the chick chorioallantoic membrane (CAM)

Evolution of the microvascular distensibility during embryo growth. Example of the chick chorioallantoic membrane (CAM). The purpose of this work was to determine the evolution of the microvascular distensibility during the embryo growth. The microvascular distensibility was involved in capillary flow regulation, therefore in tissular irrigation and capillaries network growth during the angiogenesis. Its value fluctuated with the arteriolar tone. We worked on the CAM of the chick embryo, because of the vessel wall structure quickly changes during its development. We performed the measurements at three stages of development: at day 6, day 12 and day 16 of incubation. We carried out the measurements on in situ vessels visualized by microscopy, without vasoactive substances in order to preserve the vascular tone. Each vessel was canulated with a micropipette, occluded by a distal compression and inflated with a saline injection under controlled pressures. The distensibility was expressed as the relative increase in diameter. We determined that: 1) The distensibility was significantly higher in the vessels smaller than 58 μm diameter than in the larger vessels at day 6 and day 12 (the 58 μm value was the average diameter of the studied vessels). 2) The distensibility of the arteries, whatever their diameter (small or large) significantly decreased between day 12 and day 16 of incubation. 3) The distensibility of the smallest veins significantly decreases between day 12 and day 16, whereas the distensibility of the largest veins did not change during the same period. 4) The arteriolar distensibility was significantly smaller than the venular distensibility at day 12 and day 16.