• The flat serum growth hormone (GH) patterns of untreated parkinsonian patients develop diurnal rises during treatment with levodopa. This chronic exposure to excesses of GH might lead to the eventual emergence of the "on-off" phenomenon, which would indicate a need for animal experiments. Pretreatment of mice with GH increased (1) cerebral dopa and dopamine concentrations in levodopa-treated mice, (2) cerebral accumulation of injected tritiated apomorphine and tritiated thymidine, and (3) behavioral responses to levodopa, L-m-tyrosine, apomorphine hydrochloride, and oxotremorine.
Tang LC, Cotzias GC. Modification of the Actions of Some Neuroactive Drugs by Growth Hormone. Arch Neurol. 1976;33(2):131–134. doi:10.1001/archneur.1976.00500020059009