K-stimulated release of leu- and met-enkephalin from rat striatal slices: lack of effect of morphine and naloxone.

The release of leu- and met-enkephalin from rat striatal slices was determined by superfusing the slices in vitro and running the superfusates directly over columns of Amberlite XAD-2 from which the peptides were eluted with methanol and measured by radioimmunoassay. Depolarization by high K concentrations increased the release of both pentapeptides many fold; the degree of increase, however, depended in part on the length of time chosen for the stimulation period, suggesting that the stimulation effect was very short lived. The stimulated release of both peptides (but not the resting release) was at least partially dependent on Ca in the medium and was totally inhibited by high Mg concentrations. Selected concentrations of naloxone and morphine in the superfusing medium had no effect on the resting or stimulated release of the peptides. The results support the hypothesis that these peptides serve as neurotransmitters in the striatum, but autoregulation of their release by morphine and naloxone could not be demonstrated.