Ontogenetic and Phylogenelic anaylses of factors affecting the developmental process in crine concentrating mechanism

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In our previous investigation, we demonstrated that the neonatal renal medulla is transformed from 'avian-type' to 'mammalian-type' organization of the renal tubular functions. The transformations include the disappearance of active NaCl reabsorption and emergence of large passive NaCl reabsorption in the thin ascending limb of Henle's loop, and appearance of water permeability via AQP-1 in the thin descending limb.To elucidate the mechanism of transformation in the urine concentrating system of the renal medulla, we investigated the effect of elongation of the pregnancy period, thereby examining the influence of the birth on the transformational change in the system. The prolongation of pregnancy was achieved by two methods. One method is the vaglnal ligation on the day 17 during pregnancy. Another method is the administration of progesterone to the pregnant rats. Both methods enebled us to elongate the period of pregnancy by 3 days.When we compared the maturation of the thin ascending limb of Henle's loop between day3 neonates and day 23 fetuses, the disappearance of NKCC2 immunoreactivity in the renal medulla and diminishment of the positive transepithelial voltages in the thin ascending limb were similar.These results strongly suggest that the transformational changes of the renal medullary urine concentrating system occurring during the birth is not the process dependent on the birth itself, but the process programmed in the developmental process of the kidneys.