Evidence for endogenous dopaminergic control of GH release in man

In order to determine whether or not there is a tonic dopamine (DA) control of GH release, the effect of an anti-dopaminergic agent, sulpiride, on GH secretion was studied in 12 normal subjects. After the administration of sulpiride, serum concentrations of sulpiride reached a peak value (1.93 +/- 0.1 micrograms/ml, mean +/- S.E.M., n = 6) at 15 min and then showed a gradual decrease. Concomitantly, mean plasma prolactin (PRL) showed a rapid elevation, with a peak value of 161.9 +/- 11.5 ng/ml at 30 min, followed by a gradual decrease. Even at 180 min after sulpiride injection, the plasma PRL was still 9 times higher than the initial level (p less than 0.005). Within 90 min after the injection, 12 subjects showed a minimal but significant decrease in GH (from 0.78 +/- 0.17 to 0.32 +/- 0.03 ng/ml, p less than 0.02). After another 90 min, the plasma GH level increased and the mean peak value (8.1 +/- 2.7 ng/ml) at 180 min was significantly higher than the initial value (p less than 0.02). From these observations, it was suggested that sulpiride inhibited the endogenous DA activity over 180 min, and that the GH decrease within 90 min was due to a suppression of endogenous DA activity. Factors other than DA, however, might be considered for the GH increase after 90 min.