Delbeke D, Dannies P S
Endocrinology. 1985 Aug;117(2):439-46. doi: 10.1210/endo-117-2-439.
Dopaminergic inhibition of PRL release stimulated by agents that affect cytosolic Ca2+ concentrations, C-kinase activity, and cAMP levels was studied in perifused rat anterior pituitary cells cultured on cytodex beads. We used A23187 (20 microM) to increase intracellular Ca2+, the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 50 nM) to stimulate C-kinase, forskolin (10 microM) to increase intracellular cAMP, and 8-bromo-cAMP to mimic cAMP. Dopamine (10 microM) inhibited PRL release to 20-60% of the basal release within 10 min. After 30 min of preincubation with dopamine, the absolute amount of release stimulated by 100 nM TRH was strongly inhibited, although the pattern of release, a quick burst followed by sustained release at a lower rate, was the same in the presence or absence of dopamine. A23187 (20 microM) caused a rapid burst of PRL release that subsided within 10 min, and TPA (50 nM) caused a sustained release that began within 4 min and continued for at least 30 min. TPA and A23187 combined caused a rapid burst of release followed by a sustained phase of release similar to that caused by TRH. Preincubation with dopamine inhibited the absolute amount of PRL release caused by A23187 alone, TPA alone, or the two combined, although, as with TRH, the pattern of release remained the same. Forskolin (1 or 10 microM) or 8-bromo-cAMP (3 mM) induced a 1.5- to 2-fold increase in PRL release, and this was completely prevented by dopamine. Preincubation with both dopamine and 8-bromo-cAMP or forskolin restored the amount of release stimulated by TPA alone or TPA and A23187 in the presence of dopamine to the level of release stimulated by these agents in the absence of dopamine. Therefore, activating either the cAMP messenger system or the Ca2+ system alone will not abolish dopaminergic inhibition, but activating the two together will. These results suggest that dopamine blocks release by inhibiting both adenylate cyclase and a step in the Ca2+ messenger system.
在细胞基质珠上培养的经灌注的大鼠垂体前叶细胞中，研究了多巴胺对由影响胞质Ca2+浓度、C激酶活性和cAMP水平的物质所刺激的PRL释放的抑制作用。我们使用A23187（20微摩尔）来增加细胞内Ca2+，佛波酯12-O-十四烷酰佛波醇-13-乙酸酯（TPA；50纳摩尔）来刺激C激酶，福斯高林（10微摩尔）来增加细胞内cAMP，以及8-溴-cAMP来模拟cAMP。多巴胺（10微摩尔）在10分钟内将PRL释放抑制至基础释放的20%-60%。在与多巴胺预孵育30分钟后，100纳摩尔TRH所刺激的释放绝对量受到强烈抑制，尽管释放模式，即快速爆发后以较低速率持续释放，在有无多巴胺的情况下是相同的。A23187（20微摩尔）引起PRL释放的快速爆发，在10分钟内消退，TPA（50纳摩尔）引起持续释放，在4分钟内开始并持续至少30分钟。TPA和A23187联合使用引起快速释放爆发，随后是类似于TRH引起的持续释放阶段。与多巴胺预孵育抑制了单独由A23187、单独由TPA或两者联合引起的PRL释放绝对量，尽管与TRH一样，释放模式保持不变。福斯高林（1或10微摩尔）或8-溴-cAMP（3毫摩尔）诱导PRL释放增加1.5至2倍，而这被多巴胺完全阻止。多巴胺与8-溴-cAMP或福斯高林同时预孵育，可将单独TPA或TPA与A23187在多巴胺存在下所刺激的释放量恢复到这些物质在无多巴胺情况下所刺激的释放水平。因此，单独激活cAMP信使系统或Ca2+系统不会消除多巴胺能抑制作用，但两者一起激活则会。这些结果表明，多巴胺通过抑制腺苷酸环化酶和Ca2+信使系统中的一个步骤来阻断释放。
