Early Biochemical Changes in the Embryonic Ra t Heart after Teratogen Treatment

The effects on mucopolysaccharide synthesis in isolated embryonic rat hearts of in vivo and/or in vitro 6-aminonicotinamide, dietary-induced folic acid deficiency, aminopterin, and trypan blue were investigated using uptake of 35S-sodi~m sulfate to measure the rate of mucopolysaccharide synthesis. Intraperitoneal injection of 6-aminonicotinamide on day 11 of gestation caused inhibition of mucopolysaccharide synthesis which was most pronounced at day 13. A similar effect followed in vitro 6-aminonicotinamide treatment. Maternal folic acid deficiency on days 9-11 of pregnancy caused decreased mucopolysaccharide synthesis in embryonic hearts at day 14. In vitro treatment with the folic acid antagonist aminopterin inhibited the rate of synthesis on days 13-16. In vivo trypan blue on day 9 of pregnancy had no effect on the rate of mucopolysaccharide synthesis. However, in vitro trypan blue treatment of embryonic hearts resulted in a marked depression in synthetic rate. Aminopterin and 6-aminonicotinamide had no noticeable effect on the rate of protein synthesis in isolated embryonic hearts as determined by measurement of "-leucine incorporation. Thus mucopolysaccharide synthesis in isolated embryonic rat hearts was susceptible to the action of the teratogens used. It is postulated that these teratogens act by blocking a biochemical reaction in the synthesis of mucopolysaccharides and are not affecting the cellular machinery necessary for general protein synthesis. Present knowledge of the mechanisms of action of teratogens is very limited, even in laboratory animals. It may be that many teratogens act by means of an effect on some of the large molecules important in development. Information on mechanisms of action may be provided by investigating some of the early biochemical changes in developing systems after teratogen treatment. Mucopolysaccharides of the embryonic rat heart were selected for biochemical investigation in this study. In the heart, mucopolysaccharides are found in the endocardial cushions, interatrial septum, bulbus and large blood vessels, and cardiac jelly (Walker, '61). Barry ('48) and Patton et al. ('48) described the role of the cardiac jelly as twofold: allowing the heart to function as a pump while changing shape and position during development, and serving as a substrate for the molding action of the bloodstream in shaping the heart. The TERATOLOGY, 4: 183-190. gelatinous property of mucopolysaccharides is thought to be related to these roles of the cardiac jelly (Gessner and Bostrom, '65; Gessner e t al., '65). Recent evidence has linked both inherited and experimentally produced congenital malformations to decreased mucopolysaccharide synthesis. Mathews ('67) observed decreased sulfated mucopolysaccharide in the limbs of chick embryos with inherited lethal skeletal defects. Meyer ('69) suggested that these defects may be the result of deletions of some biosynthetic enzyme systems leading to mucopolysaccharide synthesis. Teratogens have produced abnormal mucopolysaccharide synthesis in vitro (Beaudoin, Bostrom, 1 From a dissertation submitted to the Horace H. Rackham School of Graduate Studies of The University of Michigan in partial fulfillment of the requirements for the degree of Doctor of Philosophy. 2 Supported by NIH grants GM00312 and HD00400. 3 Present address: Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80302.