Urea cycle and purinolysis in the embryos and pregnant females of the teleost fish Poecilia reticulata]

The presence of a functional ornithine-urea cycle is evidenced in the embryos of the viviparous Teleost Poecilia reticulata. The activity of the cycle decreases during developmental period but persists in adult tissues. Purinolytic (uricolytic) pathway is another source of urea in both embryos and adults. The implications of these findings are briefly discussed in relation to the problems of ureogenic and ureosmotic phenomena in Teleostean Fishes.