Arginine stimulates thymic immune function and ameliorates the obesity and the hyperglycemia of genetically obese mice.

The effect of 6-day dietary arginine supplementation on the weight gain, blood glucose, thymus weight, thymic lymphocyte content, and in vitro thymic lymphocyte immune reactivity was studied in obese (C57BL/6J-OB/)B) and heterozygous lean mice. Control mice were fed a commercial laboratory chow (1.8% arginine content) and drank tap water, while supplemented mice were given 0.5% arginine in the chow and 0.5% arginine solution for drinking. All mice ate and drank ad libitum. Supplemental arginine significantly decreased the weight gain (1.2 g vs. 2.2 g, p less than 0.01) and blood glucose levels (303 mg% vs 236 mg%, p less than 0.02) of the OB/OB mice; no such effects were noted in the lean heterozygotes, all of which had normal blood glucose levels. OB/OB mice had thymus glands which weighed less and contained significantly fewer lymphocytes than their lean littermates. In vitro mitogen-stimulated thymic lymphocyte protein synthetic rates were equal in chow-fed lean and OB/OB mice. In both groups, supplemental arginine significantly increased thymus weight, the number of thymic lymphocytes per gland, and thymic lymphocyte immunoreactivity in vitro. The hormonal secretagogue activity of arginine on the pituitary may explain its beneficial effects on the rate of weight gain, hyperglycemia, and depressed thymic immune function of OB/OB mice.