Phenytoin-induced increase in growth hormone response to levodopa in adult males.

Abstract

SUMMARY Growth hormone and prolactin response to levodopa were evaluated before and after long-term phenytoin treatment in five men with previously untreated partial epilepsy. After phenytoin treatment, growth hormone response to levodopa increased. There was a close relationship between growth hormone response to levodopa and plasma phenytoin concentrations. These findings suggest a phenytoin-induced dopaminergic activity at the hypothalamic-pituitary level in adult males.Recently, Luoma et al' reported elevated serum growth hormone (GH) levels in women treated with phenytoin and carbamazepine. London et al,2 however, reported lowered response of growth hormone to insulin hypoglycaemia, unchanged baseline growth hormone levels, and increased prolactin response to thyrotropin-releasing hormone administration in healthy male volunteers after 7 days of treatment with phenytoin or carbamazepine. Such hormonal changes may be due to interaction of phenytoin or carbamazepine with the monaminergic systems that control hypothalamic-pituitary function.3Clinical findings indirectly suggest that phenytoin may interact with the dopaminergic system at the striatal level.4 Furthermore, both in vivo and in vitro laboratory studies indicate that phenytoin changes the dopaminergic activity within the central nervous system. Hadfield5 showed that dopamine uptake is inhibited by phenytoin in the striatum but stimulated in the hypothalamus; Elliott et a16 found that phenytoin reduced dopamine utilisation and induced a neuroleptic-like activity in behavioral tests on mice. Lepore et aP suggested that phenytoin may act as a dopaminergic agonist, since it reduces dopamine turnover in rat striatum.In the present study, we evaluated growth hormone and prolactin response to levodopa in epilepAddress for reprint request: