Antagonism of morphine-induced catalepsy by L-prolyl-L-leucyl-glycinamide.

In view of the recently demonstrated extra-endocrine central actions of hypothalamic releasing hormones, we have investigated the effects of prolyl-leucyl-glycinamide (PLG) and thyrotropin releasing hormone (TRH) on morphine-induced catalepsy. Although acute administration of PLG (10 mg kg-1 s.c.) slightly attenuated the cataleptic response, chronic PLG treatment (10 mg kg-1 s.c. for 10 days) virtually abolished morphine-induced catalepsy. TRH, administered subcutaneously, exhibited little or no anti-cataleptic activity. These results are discussed in relation to the possible central site of narcotic-induced catalepsy and the therapeutic potential of PLG in Parkinson's disease.