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Journal of Clinical Endocrinology & Metabolism, Vol 47, 647-652, Copyright © 1978 by Endocrine Society

ARTICLES

Carbidopa inhibits the growth hormone- and prolactin-suppressive effect of L-dopa in acromegalic patients

F Camanni, GB Picotti, F Massara, GM Molinatti, P Mantegazza and EE Muller

The plasma GH, PRL, TSH, and dopamine (DA) responses to an infusion of L-dopa were examined in six acromegalic patients before and after pretreatment with carbidopa, a drug which inhibits the peripheral conversion of L-dopa to DA. Carbidopa neither modified baseline DA nor induced changes in baseline GH, PRL, or TSH levels. The drug instead markedly reduced the L-dopa-induced DA rise, an effect which was concomitant to a striking reduction of the suppressive effect of L-dopa on plasma GH and a partial inhibition of the suppressive effect of L- dopa on plasma PRL. TSH levels did not change either after L-dopa alone or L-dopa plus carbidopa. These data demonstrate that in "responder" acromegalics, L-dopa inhibits GH secretion through its peripheral conversion to DA and not via activation of central DA neurotransmission. For the effect of L-dopa on PRL secretion, in addition to a peripheral dopaminergic component, a central component cannot be disregarded.




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