Relation of arginine nutrition to mammary gland development

Experiments were conducted to determine the effect of dietary arginine on mammary gland development in gravid and nongravid rats. Dietary arginine ranged from 0% to 0.75%. All rats were weighed and euthanized within 8 h after parturition. Both mature and nongravid rats fed arginine-free diets remained in positive nitrogen balance but lost body weight. However, as little as 0.15% dietary arginine increased nitrogen retention nearly 3-fold and prevented weight loss. Number of pups born and their birth weight were not affected by dietary arginine. Consumption of an arginine-free diet during gestation significantly reduced mammary gland weight and mammary gland weight as a percent of body weight. Depression in mammary gland weight was associated with depressed significantly mammary RNA and DNA concentrations. However, the RNA:DNA ratio was not affected by dietary arginine. Increased mammary mass and nucleic acid content was not attributed to increased feed intake, since feed intake of gestating rats increased only 35% while arginine intake increased by 300%. Restricting feed intake by pair-feeding resulted in body weight loss; however, mammary gland mass and nucleic acid content were significantly higher than that of rats fed an arginine free diet. Arginase and S-adenosyl-L-decarboxylase activities were not affected by dietary arginine concentration. Arginine level significantly affected ornithine decarboxylase activity, but the effect was inconsistent. There was a high correlation between ornithine decarboxylase activity and RNA concentration. Restricting arginine or feed intake during early gestation followed by excess intake of arginine or feed resulted in compensatory growth of rat mammary glands. Arginine requirement for nongravid and gravid rats based upon nitrogen retention and body weight gain was estimated to be 0.21% and 0.55%, respectively. This study demonstrated that dietary arginine is required for optimal mammary gland development during gestation. It appears that the effect of arginine is not mediated directly via ornithine decarboxylase.