Dose-related effect of the oxytocin fragment (prolyl-leucyl-glycinamide) on ?-MPT-induced catecholamine disappearance and serotonin level in rat brain.

Graded doses of Pro-Leu-Gly-NH(2) (3.5 x 10(?12), 3.5 x 10(?11), 3.5 x 10(?10) or 3.5 x 10(?9) mol) were administered into the lateral cerebral ventricle of rats. The noradrenaline level of the dorsal hippocampus was increased 30 min after a dose of 3.5 x 10(?10) mol Pro-Leu-Gly-NH(2). The dopamine level was increased in the dorsal hippocampus and in the striatum. The serotonin level was increased in the hypothalamus, in the striatum and decreased in the dorsal hippocampus. The catecholamine disappearance following 350 mg/kg of ?-methyl-p-tyrosine indicated an accelerated dopamine disappearance in the striatum for each dose studied, while the hypothalamic noradrenaline disappearance was inhibited by a dose of 3.5 x 10(?11) mol of Pro-Leu-Gly-NH(2). The data indicate that Pro-Leu-Gly-NH(2) induces dose and region-dependent changes in the cerebral monoamine metabolism. The striatal dopamine and hypothalamic serotonin metabolism appeared to be the most sensitive for intraventricular Pro-Leu-Gly-NH(2).