[Development of the capillaries of the primary portal plexus of the hypothalamus in rats in the perinatal period].

The structure of capillaries of the primary portal plexus in rats was studied on the 18th day of prenatal period and ist and 9th days of postnatal period. The number of capillaries and capillary loops penetrating in the nervous tissue of median eminence increases during development. The endothelial cells divide and differentiate and this is accompanied by the decrease in the volume of perikaryons, the flattening of peripheral cell regions and the increase in the number of fenestrae. The greatest number of pinocytotic vesicles is noted in the newborn rats. The morphometrical data obtained suggest indirectly the transport of substances through the wall of capillaries in foetuses and newborn rats mainly via pinocytotic vesicles and on the 9th day of life via fenestrae.