SHORT-TERM NEUROENDOCRINE EFFECTS OF A LARGE ORAL DOSE OF MONOSODIUM GLUTAMATE IN FASTING MALE-SUBJECTS

Fasting male subjects received each of four treatments on different da ys: a large oral dose of monosodium L-glutamate (MSG; 12.7 g), the MSG vehicle, an iv injection of TRH, or a high protein meal. Blood sample s were drawn via an indwelling venous line before and at 20-min interv als after each treatment for 4 h. Plasma glutamate levels rose 11-fold within 1 h of MSG ingestion, but did not change appreciably with any of the other treatments. Plasma PRL levels rose 10-fold after TRH infu sion and 2-fold after the protein meal, but did not rise significantly after MSG ingestion. No effects resulted from any of the treatments o n plasma LH, FSH, testosterone, GH, or cortisol concentrations. Plasma levels of TSH, T-4, and T-3 showed minimal changes after any of the t reatments except TRH; TRH elevated plasma TSH and T-3 levels. Self-rat ing instruments of mood and side-effects revealed no treatment-related effects on mood or physical state for up to 48 h after each treatment . Together, these results suggest that acute pharmacological elevation s of plasma glutamate levels in adult men produce minimal, if any, eff ects on hypothalamic or pituitary function.