Schwarzschild M A, Vale W, Corigliano-Murphy A C, Pisano J J, Ip N Y, Zigmond R E
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
Neuroscience. 1989;31(1):159-67. doi: 10.1016/0306-4522(89)90037-7.
The hydroxylation of tyrosine to dopa is the rate-limiting reaction in catecholamine biosynthesis. It has been previously reported that secretin, vasoactive intestinal peptide and peptide histidine isoleucine amide, all members of the secretin-glucagon family of peptides, increase dopa synthesis in superior cervical ganglia in vitro. We report here that two other members of this peptide family, rat growth hormone-releasing factor and helodermin H38, a component of Gila monster venom, also increase the rate of dopa synthesis, while glucagon-like peptides I and II and a number of other peptides tested produce no effect. Since analogs of cAMP also increase dopa synthesis, it is of particular interest that all of the peptides that increase catechol synthesis also raise the levels of this cyclic nucleotide in the superior cervical ganglion. Helodermin H38 stimulated the rate of dopa synthesis and the level of cAMP with similar potencies (EC50S of approximately 10 nM) and with maximal effects of two- and two-fold, respectively. By either measure, rat growth hormone-releasing factor produced a two-fold increase at 10 microM and a three- to four-fold increase at 30 microM. Analogs of peptides of the secretin-glucagon family with a deletion or modification of the N-terminal histidine were much less effective in these assays at the concentrations tested than were their parent compounds, demonstrating an important role for this amino acid in conferring activity on these peptides. In addition to increasing dopa synthesis in intact tissue, incubation of ganglia with rat growth hormone-releasing factor, secretin, vasoactive intestinal peptide or peptide histidine isoleucine amide also increased the activity of tyrosine hydroxylase measured subsequently in ganglion homogenates. Thus, the peptidergic stimulation of dopa synthesis observed in the intact superior cervical ganglion appears to be due, at least in part, to the activation of tyrosine hydroxylase. Together with previous studies, these findings support the hypothesis that certain members of the secretin-glucagon family increase catecholamine synthesis in sympathetic neurons by a cAMP-dependent activation of tyrosine hydroxylase.
酪氨酸羟化生成多巴是儿茶酚胺生物合成中的限速反应。此前有报道称，促胰液素、血管活性肠肽和肽组氨酸异亮氨酸酰胺，这些促胰液素 - 胰高血糖素家族肽的所有成员，在体外可增加颈上神经节中的多巴合成。我们在此报告，该肽家族的另外两个成员，大鼠生长激素释放因子和希拉毒蜥毒液成分希拉毒素H38，也能增加多巴合成速率，而胰高血糖素样肽I和II以及其他一些测试过的肽则没有效果。由于环磷酸腺苷（cAMP）类似物也能增加多巴合成，特别有趣的是，所有增加儿茶酚合成的肽也会提高颈上神经节中这种环核苷酸的水平。希拉毒素H38刺激多巴合成速率和cAMP水平的效力相似（半数有效浓度约为10 nM），最大效应分别为两倍和两倍。通过任何一种测量方法，大鼠生长激素释放因子在10 μM时增加两倍，在30 μM时增加三到四倍。在这些测定中，促胰液素 - 胰高血糖素家族肽的N端组氨酸缺失或修饰的类似物在测试浓度下比其母体化合物效果差得多，表明该氨基酸在赋予这些肽活性方面起着重要作用。除了增加完整组织中的多巴合成外，用大鼠生长激素释放因子、促胰液素、血管活性肠肽或肽组氨酸异亮氨酸酰胺孵育神经节，随后在神经节匀浆中测量的酪氨酸羟化酶活性也会增加。因此，在完整的颈上神经节中观察到的肽能刺激多巴合成似乎至少部分是由于酪氨酸羟化酶的激活。与先前的研究一起，这些发现支持这样的假设，即促胰液素 - 胰高血糖素家族的某些成员通过cAMP依赖性激活酪氨酸羟化酶来增加交感神经元中的儿茶酚胺合成。
