Abstract
The role of endogenous dopamine (DA) on plasma GH secretion was studied using domperidone (DA receptor blocker which does not cross blood brain barrier) in 16 normal subjects. After a bolus injection of domperidone (10 mg, i.v.), plasma PRL in 11 cases rose quickly and markedly from the basal level of 9.5 +/- 1.2 ng/ml (Mean +/- S.E.) to a maximum of 76.3 +/- 10.6 ng/ml at 30 min. In contrast, plasma GH in these cases showed a delayed and slight increases to domperidone injection where the values at 90 min and 120 min (3.5 +/- 0.8 ng/ml and 3.7 +/- 1.0 ng/ml) were significantly higher than those in control study (1.2 +/- 0.2 ng/ml and 1.0 +/- 0.1 ng/ml; p less than 0.05; n = 8). Domperidone infusion (0.22 mg/min/3 hr) was performed in the remaining 5 subjects. The plasma PRL responses were similar to those in the bolus injection of domperidone. These PRL responses were not modified when L-dopa was administered 30 min after the start of iv infusion of domperidone. Plasma GH showed slight but significant increases 135 min after the infusion compared to control study (4.3 +/- 1.2 ng/ml vs. 1.0 +/- 0.1 ng/ml; p less than 0.05). By the prior infusion of domperidone plasma GH responses to L-dopa was delayed and blunted, i.e., the occurrence of elevation and peak value of GH delayed by 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)
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