Monosodium glutamate and pituitary gland luteinizing hormone (LH) release in response to LH-releasing hormone: an in vitro study.

We studied whether an increase in the basal LH release rate and/or the anterior pituitary gland (APG) LH response to LHRH is involved in maintaining normal or near-normal serum LH levels in monosodium L-glutamate (MSG)-treated rats which have small APGs for their body weight. Female rats were injected with MSG (4 mg/g BW) or saline on days 1, 3, 5, 7, and 9 after birth (day of birth = 0). At 8-9 weeks of age, saline-treated and MSG-treated rats were ovariectomized, and 7 days later, they were decapitated. Trunk blood was collected from 18 controls and 19 MSG-treated rats, and serum LH concentrations were measured by RIA. APGs were bisected and each hemi-APG was placed in culture medium for a 30-min preincubation period, followed by two 30-min incubation periods during which water or 10 or 30 ng LHRH were added to the medium. Despite the fact that the APGs of the MSG-treated rats were half the size of those of the saline-treated rats, the serum LH levels in the 2 groups were not different. Basal LH release rates (the response to water) and LHRH-induced LH release per mg APG were increased in MSG-treated rats. Calculation of the basal LH release rates and LHRH-induced LH release on the basis of the entire weights of the APGs showed no differences between the MSG-treated rats and the controls. In 6 additional control and 6 additional MSG-treated rats, the APG LH concentration was measured and was not different between the 2 groups. The results suggest that increases in both the basal LH release rate per mg APG and the amount of LH released per mg APG in response to LHRH are of importance in the maintenance of normal or near-normal serum LH concentrations in MSG-treated rats with small APGs.