Racké K, Böhm E, Muscholl E
Naunyn Schmiedebergs Arch Pharmacol. 1987 Jan;335(1):21-7. doi: 10.1007/BF00165030.
Isolated rat NILs were incubated in Krebs-HEPES solution. The release of dopamine and its metabolites (DOPAC, HVA and MOPET) was determined by HPLC with electrochemical detection. The spontaneous release of the sum of metabolites was about 40 times that of dopamine. The spontaneous outflow of dopamine metabolites was unaffected after inhibition of dopamine uptake (by GBR 12921) or after pretreatment with reserpine (5 mg/kg, 12 h before the experiments), but it was reduced by 50% after preincubation with the irreversible DOPA decarboxylase inhibitor, (MFMD, 10 microM, for 10 min). The combination of pretreatment with reserpine and preincubation with MFMD resulted in an 80% inhibition of the spontaneous outflow of dopamine metabolites. Treatment with reserpine caused a 98% depletion of the dopamine tissue content, whereas 60 min after exposure to MFMD the dopamine tissue content was decreased by 40%. Electrical stimulation of the pituitary stalk (3-15 Hz, in the presence of GBR 12921) caused a frequency-dependent release of dopamine. Stimulation at 7 or 15 Hz caused also a significant release of dopamine metabolites. After pretreatment with reserpine, the release of dopamine evoked by stimulation at 15 Hz was abolished, whereas the evoked release of the metabolites was only reduced by about 55%. After MFMD, the evoked release of dopamine decreased by a percentage similar to that of dopamine tissue content, but the reduction of the evoked release of metabolites was more pronounced. In conclusion, the spontaneous release of dopamine metabolites from the dopaminergic nerve endings in the NIL largely reflects the catabolism of newly synthesized dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)
分离出的大鼠中间叶（NIL）在Krebs-HEPES溶液中孵育。通过高效液相色谱电化学检测法测定多巴胺及其代谢产物（3,4-二羟基苯乙酸、高香草酸和3-甲氧基酪胺）的释放量。代谢产物总和的自发释放量约为多巴胺的40倍。抑制多巴胺摄取（通过GBR 12921）或用利血平预处理（5mg/kg，实验前12小时）后，多巴胺代谢产物的自发流出不受影响，但在与不可逆的多巴脱羧酶抑制剂（MFMD，10μM，孵育10分钟）预孵育后，其自发流出减少了50%。利血平预处理和MFMD预孵育相结合导致多巴胺代谢产物的自发流出受到80%的抑制。利血平处理使多巴胺组织含量减少98%，而暴露于MFMD 60分钟后，多巴胺组织含量减少40%。垂体柄电刺激（3-15Hz，在GBR 12921存在下）引起多巴胺的频率依赖性释放。7或15Hz刺激也导致多巴胺代谢产物的显著释放。利血平预处理后，15Hz刺激引起的多巴胺释放被消除，而代谢产物的诱发释放仅减少约55%。MFMD处理后，多巴胺的诱发释放减少的百分比与多巴胺组织含量相似，但代谢产物诱发释放的减少更为明显。总之，NIL中多巴胺能神经末梢多巴胺代谢产物的自发释放很大程度上反映了新合成多巴胺的分解代谢。（摘要截断于250字）
