Neonatal treatment with monosodium glutamate increases plasma corticosterone in the rat.

Monosodium glutamate (MSG) has been shown to alter several neuroendocrine functions in neonatally treated rats. To evaluate for possible alterations in the hypothalamic-pituitary-adrenal axis, we injected rats during the neonatal period with MSG or saline (controls). An increase in basal plasma corticosterone levels associated with a blunted circadian variation was observed. Ether exposure produced a significant elevation in plasma corticosterone concentration in both groups of animals. However, while the increase in controls was 181.3% for male and 193.9% for female rats, in the MSG-treated rats it was only 60.7 and 31.6%, respectively. The intraperitoneal administration of high dexamethasone doses blocked corticosterone secretion in both groups. However, whereas the lowest dose (0.10 microgram/kg) suppressed corticosterone secretion in control animals, it was ineffective in MSG-treated rats. The morphological study of adrenals revealed signs of a hyperfunctional state in MSG-treated rats. These data suggest that the central lesions produced by MSG treatment disrupt the regulation of the hypothalamic-pituitary-adrenal axis.