Abstract
Plasma GH response to human GH-releasing factor (GRF) was examined in adult female rats that had been treated with monosodium glutamate (MSG ; 4 mg/g BW, sc) for 5 days during the neonatal period. Rats given MSG had reduced nasal-anal length and revealed obesity compared to the control rats. Five months after MSG treatment, when the animals were killed by decapitation, it was found that their immunoreactive GRF content in the pituitary stalk-median eminence tissue was less than 20% of that of the control group and their anterior pituitary weight had decreased. However, the concentration of GH had not altered.
Under pentobarbital anesthesia, basal plasma GH levels were significantly reduced in MSG-treated rats as compared to the control rats. A significant dose-dependent plasma GH response was observed after the administration of two doses of human GRF (0.25 and 1 μg/kg BW, iv) in the control group and MSG-treated rats. The responses among MSG-treated rats did not differ from those in the control rats.
These results show that the pituitary's responsiveness to exogenous GRF is well preserved in MSG-treated rats despite prolonged and severe depletion of endogenous GRF.
