AFFERENT PORTAL VENOUS SYSTEM IN THE MESONEPHROS AND METANEPHROS OF CHICK-EMBRYOS - DEVELOPMENT AND DEGENERATION

Background: In the chick embryo, both mesonephros and metanephros have a renal portal system. The classical Literature gives uncertain answe rs about the development and degeneration of the meso- and metanephric portal venous system. Some mesonephric vessels present angiogenic pro cesses to colonize the metanephros, while others show signs of degener ation and disappear together with the mesonephros. The adult avian kid ney has a conspicuously placed valve, the renal portal valve. The deve lopment of this functionally important renal portal valve has not yet been studied in detail. Methods: Scanning electron microscopy of vascu lar corrosion casts has been used in this study. Strong mesonephric de generation as well as metanephric growth and maturation occur in the d evelopmental stages selected for this investigation (7.5, 9, 11, 14, a nd 21 days of incubation). Results: The mesonephric afferent venous sy stem in the chick embryo is supplied by two vessels, the posterior and the anterior mesonephric portal veins. The posterior mesonephric port al veins show a similar pattern to the anuran (amphibian) kidney. The anterior mesonephric portal vein has not previously been described. Co nstrictions were found in this vessel, a probable sign of subsequent d egeneration. The metanephric afferent venous system is also supplied b y two vessels: the caudal and cranial metanephric portal veins. The ca udal metanephric portal vein is derived from the postcardinal vein. Th e cranial metanephric portal vein grows independently throughout the d evelopment of the mesonephric vascular system. It is connected to the vertebral venous sinus already at the beginning of its development. Th e renal portal valve first appears as a capillary network that communi cates with the developing afferent and efferent metanephric venous sys tems. This capillary network later develops to a venous valve. The met anephric afferent venous system shows typical angiogenic signs in corr osion cast, such as nodular protrusions, holes, and enlarged vessels. Conclusions: The postcardinal vein first supplies only the mesonephric tissue as a portal vessel. Then it becomes a common source for both k idney generations. Finally it supplies only the metanephric tissue wit h venous blood. However, two independent vessels were found to supply the cranial renal regions: the anterior mesonephric portal vein and th e cranial metanephric portal vein. (C) 1997 Wiley-Liss, Inc.