Keywords: Parkinson's disease; Levodopa; GH; Exercise INHIBITORY EFFECT OF CIMETIDINE ON L-DOPA-STIMULATED GROWTH HORMONE RELEASE IN NORMAL MAN A. ZANOBONI, G. GALMOZZI, S. MARINONI, WANDA ZANOBONI-MUCIACCIA SUMMARY Some evidence suggests the existence of a histaminergic influence on GH secretion in animals and man. We used cimetidine, a specific H2-receptor antagonist, to study the possible interference of H2-receptor blockade on plasma GH release by L-dopa and on PRL inhibition by L-dopa in normal man. Seven healthy normal male volunteers aged 23–36 years received a single oral dose of L-dopa (500 mg) or an i.v. bolus of cimetidine (300 mg) or both (L-dopa 30 min before cimetidine). Blood samples were taken at various times over 2 h and plasma GH and PRL levels measured. Cimetidine alone did not alter basal plasma GH values; L-dopa elicited the well-known GH releasing effect with peak values at 75 min (15.65 ± 2.8 ng/ml); cimetidine injected 30 min after L-dopa ingestion significantly blunted the GH response to L-dopa and peak values (4.7 ± 1.6 ng/ml) were delayed to 105 min. Cimetidine provoked a rapid rise in plasma PRL with the peak value of 15 ± 3 ng/ml at 15 min, followed by a return to near basal values in min. L-Dopa completely inhibited the PRL response to cimetidine. We conclude that there is an inhibitory influence of the H2-receptor antagonist cimetidine on GH release by L-dopa. This, together with the action of cimetidine on PRL secretion (with or without L-dopa), suggests a possible antidopaminergic effect of H2-receptor blockade at the level of the central nervous system.
Keywords: Parkinson's disease; Levodopa; GH; Exercise INHIBITORY EFFECT OF CIMETIDINE ON L-DOPA-STIMULATED GROWTH HORMONE RELEASE IN NORMAL MAN A. ZANOBONI, G. GALMOZZI, S. MARINONI, WANDA ZANOBONI-MUCIACCIA SUMMARY Some evidence suggests the existence of a histaminergic influence on GH secretion in animals and man. We used cimetidine, a specific H2-receptor antagonist, to study the possible interference of H2-receptor blockade on plasma GH release by L-dopa and on PRL inhibition by L-dopa in normal man. Seven healthy normal male volunteers aged 23–36 years received a single oral dose of L-dopa (500 mg) or an i.v. bolus of cimetidine (300 mg) or both (L-dopa 30 min before cimetidine). Blood samples were taken at various times over 2 h and plasma GH and PRL levels measured. Cimetidine alone did not alter basal plasma GH values; L-dopa elicited the well-known GH releasing effect with peak values at 75 min (15.65 ± 2.8 ng/ml); cimetidine injected 30 min after L-dopa ingestion significantly blunted the GH response to L-dopa and peak values (4.7 ± 1.6 ng/ml) were delayed to 105 min. Cimetidine provoked a rapid rise in plasma PRL with the peak value of 15 ± 3 ng/ml at 15 min, followed by a return to near basal values in min. L-Dopa completely inhibited the PRL response to cimetidine. We conclude that there is an inhibitory influence of the H2-receptor antagonist cimetidine on GH release by L-dopa. This, together with the action of cimetidine on PRL secretion (with or without L-dopa), suggests a possible antidopaminergic effect of H2-receptor blockade at the level of the central nervous system.
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