Regional differences in the effect of pargyline on dopamine concentrations in the rat hypophysis

Dopamine concentrations were estimated in different regions of the infundibular-pituitary system of the rat. The highest values were found in the pituitary stalk where they are comparable to the concentrations in the striatum, and higher than in the median eminence. In the anterior lobe the dopamine (DA) concentrations of the upper pole (10% of the lobe tissue) were 2-5 times higher than in the rest of the lobe. Anterior lobe DA was significantly higher in rats about 6 months old than in rats about 3 months old. After inhibition of MAO, the DA concentrations in the isolated neural lobe (NL) were more than doubled. In contrast there was no increase in the DA concentrations of the intermediate lobe, an observation which is in agreement with our previous finding that DA synthesis in the intermediate lobe after electrical stimulation of the pituitary stalk is much slower than in the neural lobe. Pargyline treatment caused an increase in the DA concentrations in the anterior lobe by about 150%. This rise (together with a DA increase in the stalk-infundibulum) may be related to the decrease in circulating prolactin which occurs in pargyline treated rats.