Embryonic development and mitochondrial function. 1. Effects of chloramphenicol infusion on the synthesis of cytochrome oxidase and DNA in rat embryos during late organogenesis.

Cytochrome oxidase, which is partially synthesized by the mitochondrion, was used as a measure for the development of mitochondrial function in rat embryos during the late stage of organogenesis. For this purpose the specific inhibitor of mitochondrial protein synthesis, chloramphenicol (CAP), served as a tool. Due to the rapid elimination rate of CAP from rats, a method for continuous infusion which would not cause immobilization to the animals was devised. 1. Pharmacokinetic studies proved that CAP reaches the embryo before placentation. Concentrations of CAP in the embryo are as high as they are in the maternal serum (about 20 mug/ml serum or g embryo) and thuse are sufficiently in supply for the inhibition of mitochondrial proteins synthesis, if 1000 mg/kg CAP are infused intravenously per 24 hrs. CAP is partially excluded from the embryonic compartment after the placental barrier has fully developed: whereas CAP concentration in the maternal serum remains at about 20 mug/ml, the concentration in the embryonic compartment drops to about 10 mug/g embryonic tissue during day 13 of gestation. 2. The average cytochrome oxidase activity per cell is very low (about 1 nmole O2/min X mug DNA-1) in embryonic tissue as it is in many other rapidly proliferating tissues. It is 15-60 times higher in slowly proliferating tissues, as, for example, the adult rat liver or brain (greater than 14 nmoles O2/min X mug DNA-1). 3. When the infusion technique is applied on day 12 of gestation, a sufficiently high concentration of CAP in embryonic tissue can be obtained to inhibit the synthesis of cytochrome oxidase. In constrast to tissues of an adult organism-as in the case of liver after partial hepatectomy- in embryonic tissues this limitation in the availablity of cytochrome oxidase appearently results in a critical reduction of energy production, which subsequently affects the DNA synthesis and embryonic growth. 4. The possible relevance and applicability of these experimental findings to man is discussed.