A delayed LH/FSH rise after gonadectomy and a delayed serum TSH rise after thyroidectomy in monosodium-L-glutamate (MSG)-treated rats.

The serum LH and FSH rise after gonadectomy and the serum TSH rise after thyroidectomy were examined in rats that received monosodium-L-glutamate (MSG) as neonates. The rise in serum gonadotrophins after gonadectomy was significantly delayed in both adult and peripubertal MSG-treated rats when compared to control castrates. Serum LH and FSH levels, however, eventually achieved levels in MSG-treated rats that were not significantly different than those of controls. The serum TSH rise after thyroidectomy was significantly delayed in adult female MSG-treated rats, but not in prepubertal female MSG-treated rats. Pituitary responsiveness to both exogenous LH-RH and TRH was unaffected by neonatal MSG treatment, with one exception: pituitary responsiveness to HL-RH of orchidectomized peripubertal males was blunted significantly. The results are discussed in terms of the possible neurotoxic effects of neonatal MSG treatment, as well as the altered hypothalamic sensitivity to gonadal steroids.