In vivo neurotransmitter levels in the anterior pituitary of freely behaving intact and castrated male rats determined with push-pull perfusion and high pressure liquid chromatography coupled with electrochemical detection.

Push-pull cannulae were implanted into the anterior pituitary lobes of intact and castrated male rats, and perfusate samples were assayed for neurotransmitter concentrations with HPLC coupled with electrochemical detection. Epinephrine, which was not obtained in any of the five intact males, was detectable in three of five castrated male rats. Norepinephrine rose from nondetectable to high levels after castration in all animals. In contrast to dopamine, which was significantly decreased in castrated males, levels of 3,4-dihydrophenylacetic acid and 5-hydroxyindolacetic acid were significantly increased in castrated vs. intact male rats. Homovanillic acid was rarely detected in either intact or castrated males. These results demonstrate that the push-pull perfusion technique can be used to measure neurotransmitter levels in the anterior pituitary lobes of living rats. More importantly, after castration a distinct rise in norepinephrine and epinephrine accompanied by a decrease in dopamine was clearly detected, suggesting that these neurotransmitters may play an important role directly at the pituitary.