Abstract: Wistar newborn rats were injected subcutaneously with monosodium glutamate (MSG<320 mg). On the 52 th day, the body weight, length and the weight of immune organs——thymus and spleen were reduced significantly as compared with those in the normal rats. The immune function of rats was lower than that of the normal rats ( P<001).Morphological observation showed: The nucleus arcuatus was apparently smaller and the number of neurones became obviouly less than those in the normal rats. The results of immunohistochemical tests revealed that the number of the growth hormone secreting cells in the pituitary glands of rats treated with MSGbecame smaller. We consider that :① The reason for retarded growth of pituitary glands and immune organs is the damage of nucleus arcuatus induced by MSG, thus decreasing the secretion of growth hormone releasing factor(GHRF), therefor the secretion of growth hormone in pituicyte is insufficient. ② Poor growth of the immune organs(thymus and spleen) affects the normal development and normal immune response of T,Blymphocytes in the organs. So the immune function of rats treated with MSGis reduced.

Key words: monosodium glutamate (MSG), nucleus arcuatus, immune function