Absence of growth hormone response to L-dopa and bromocriptine in hyperprolactinemic women with pituitary microadenoma.

The administration of an amino acid precursor of both dopamine and norepinephrine, L-dopa, or of a dopamine agonist, bromocriptine, did not alter basal GH secretion in hyperprolactinemic women with pituitary microadenoma, whereas both significantly increased serum GH levels in normal women. The findings cannot be accounted for by decreased pituitary GH reserve, since in hyperprolactinemic women, insulin elicited an increase in GH levels similar to its action in normal women. Thus, the mechanism by which L-dopa or bromocriptine stimulates GH secretion appears to be different from that of insulin.