Racké K, Abel D, Muscholl E
Neuroscience. 1985 Nov;16(3):501-10. doi: 10.1016/0306-4522(85)90188-5.
Neurointermediate lobes of the rat pituitary gland were incubated with [3H]dopamine in the presence of desipramine and then superfused with radioactivity-free medium. The outflow of tritium was studied and in most experiments [3H]dopamine and its metabolites were separated by column chromatography. After 60-70 min of superfusion, the spontaneous rate of tritium outflow was 1.2%/min. The spontaneously released radioactivity consisted of 52% O-methylated and deaminated metabolites, 28% 3,4-dihydroxyphenylacetic acid, 18% dopamine and 2% 3-methoxytyramine. In the presence of pargyline (10 microM) the spontaneous rate of total tritium outflow decreased by 46%, that of the O-methylated and deaminated metabolites by 72% and that of 3,4-dihydroxyphenylacetic acid by 79%. The spontaneous rate of outflow of dopamine was unchanged and that of 3-methoxytyramine increased 3-fold. Further addition of nomifensine (10 microM) doubled the rate of outflow of dopamine and 3-methoxytyramine, but had no effect on the other metabolites. Electrical stimulation of the pituitary stalk (0.2 ms, 80 V, 3 Hz, 2 min) caused a tritium release of 8.5% of the tissue tritium. The evoked tritium release was only partially dependent on the extracellular calcium and not affected by tetrodotoxin. In contrast, vasopressin release evoked by stimuli of the same strength was completely calcium-dependent and blocked by tetrodotoxin. After modification of the stimulation conditions (1 ms, 10 V, 10 Hz, 2 min) the evoked tritium release was 4.1% of the tissue tritium. This tritium release was reduced by 73% in the presence of tetrodotoxin. The total evoked tritium release was decreased by 30% in the presence of pargyline and increased by 150% after further addition of nomifensine. Under the latter conditions, tetrodotoxin reduced the evoked tritium release by 67%, but nearly all of the tetrodotoxin-resistant tritium release could be identified as dopamine metabolites. Thus, the electrical stimulation appears to liberate some [3H]dopamine metabolites from an extraneuronal compartment. In conclusion, oxidative deamination and O-methylation are important pathways of the catabolism of dopamine in the neurointermediate lobe of the pituitary gland. After labelling of the transmitter stores with [3H]dopamine, the total tritium release is a poor indicator of [3H]dopamine release from the nerve terminals. Only the isolated [3H]dopamine fraction appears to reflect the release of neuronal [3H]dopamine.
将大鼠垂体神经中间叶与[3H]多巴胺在去甲丙咪嗪存在的情况下进行孵育，然后用无放射性的培养基进行灌流。对氚的流出情况进行了研究，在大多数实验中，[3H]多巴胺及其代谢产物通过柱色谱法进行分离。灌流60 - 70分钟后，氚的自发流出率为1.2%/分钟。自发释放的放射性物质包括52%的O - 甲基化和脱氨基代谢产物、28%的3,4 - 二羟基苯乙酸、18%的多巴胺和2%的3 - 甲氧基酪胺。在存在帕吉林（10微摩尔）的情况下，总的氚流出自发率降低了46%，O - 甲基化和脱氨基代谢产物的自发率降低了72%，3,4 - 二羟基苯乙酸的自发率降低了79%。多巴胺的自发流出率未改变，而3 - 甲氧基酪胺的自发流出率增加了3倍。进一步添加诺米芬辛（10微摩尔）使多巴胺和3 - 甲氧基酪胺的流出率增加了一倍，但对其他代谢产物没有影响。对垂体柄进行电刺激（0.2毫秒，80伏，3赫兹，2分钟）导致氚释放量为组织中氚含量的8.5%。诱发的氚释放仅部分依赖于细胞外钙，且不受河豚毒素的影响。相比之下，相同强度刺激诱发的血管加压素释放完全依赖于钙，并被河豚毒素阻断。改变刺激条件（1毫秒，10伏，10赫兹，2分钟）后，诱发的氚释放量为组织中氚含量的4.1%。在存在河豚毒素的情况下，这种氚释放减少了73%。在存在帕吉林的情况下，总的诱发氚释放减少了30%，进一步添加诺米芬辛后增加了150%。在后者条件下，河豚毒素使诱发的氚释放减少了67%，但几乎所有抗河豚毒素的氚释放都可被鉴定为多巴胺代谢产物。因此，电刺激似乎从神经外间隙释放了一些[3H]多巴胺代谢产物。总之，氧化脱氨基和O - 甲基化是垂体神经中间叶中多巴胺分解代谢的重要途径。用[3H]多巴胺标记递质储存后，总的氚释放并不是神经末梢[3H]多巴胺释放的良好指标。只有分离出的[3H]多巴胺部分似乎反映了神经元[3H]多巴胺的释放。
