Monosodium glutamate: acute and chronic effects on rhythmic growth hormone and prolactin secretion, and somatostatin in the undisturbed male rat.
The present in investigation was designed to determine the chronic effects of neonatal monosodium glutamate (MSG) administration (4 g/kg s.c.) and the acute effects of MSG (1 g/kg i.p.) on episodic growth hormone (GH) and prolactin (PRL) secretion and brain somatostatin (SRIF) in unanesthetized, chronically cannulated male rats. Adult rats showed the typical physical characteristics that result from neonatal MSG administration. Analysis of episodic GH secretion showed a significant reduction in : (1) the amplitude of GH secretory peaks. and (2) the mean 5.5-h plasma level of GH. Bursts of plasma PRL were inhibited by MSG, but the mean 5.5-h plasma levels were not affected. SRIF concentrations in the medial basal hypothalamus were reduced by 60% after neonatal MSG. Acute administration of MSG to adult rats caused an immediate, long-lasting suppression of rhythmic GH secretion and a rapid, transient release of PRL. These results suggest: (1) neonatally administered MSG causes a marked disturbance in episodic GH and PRL secretion in adult rats; (2) MSG induces a decrease in hypothalamic SRIF and possibly GH-releasing factor; and (3) the acute effects of MSG on GH and PRL may be due to the inhibition and/or excitation of a complex neuronal network involving monoaminergic and peptidergic systems.
D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D001921:Brain / Q000187:drug effects; D002940:Circadian Rhythm / Q000187:drug effects*; D004334:Drug Administration Schedule; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D013006:Growth Hormone / Q000097:blood*; D007031:Hypothalamus / Q000187:drug effects; D008297:Male; D009474:Neurons / Q000187:drug effects; D011247:Pregnancy; D011388:Prolactin / Q000097:blood*; D051381:Rats; D012970:Sodium Glutamate / Q000494:pharmacology*; D013004:Somatostatin / Q000097:blood*
D005971:Glutamates; D013004:Somatostatin; D011388:Prolactin; D013006:Growth Hormone; D012970:Sodium Glutamate