Contribution of Nerve Growth Factor to The Increased Sympathetic Nerve Activity in Hypertension

在自发性高血压大鼠（SHR）和人类原发性高血压中，交感神经活动增加。特别是在SHR中，交感神经支配增加和血管组织中去甲肾上腺素（NE）释放增加已被报道，其确切机制尚不清楚。为了阐明神经生长因子（NGF）在SHR交感神经活动增加中的作用，我们检测了培养的血管平滑肌细胞（VSMCs）分泌NGF的情况，并测定了SHR和对照Wistar-Kyoto大鼠（WKY）各组织中NGF的含量。我们还观察了NGF对交感神经末梢释放NE的影响。根据Bocchini’s法从小鼠颌下腺中纯化NGF。采用外植体法制备WKY主动脉VSMCs。采用生物法测定NGF活性，酶免疫法测定NGF含量。采用灌注肠系膜动脉制备方法，观察NGF对电刺激下NE溢出的影响。1) VSMCs制备的条件培养基对感觉和交感神经元具有神经突延伸作用，这种作用可被抗ngf血清阻断。2) 3周龄时，SHR的脾脏、坐骨神经和肠系膜动脉中NGF含量高于WKY。然而，在成年动物中没有观察到这些差异。3)原位杂交显示，NGFmRNA在肠系膜动脉介质中表达升高。4)体外培养的VSMCs与肠系膜动脉、主动脉段的NGF分泌量在原位杂交下无显著差异。5) NGF以剂量依赖的方式抑制交感神经末梢电刺激引起的NE溢出。神经元摄取阻滞剂地西帕明（5x10-8M）的存在也会抑制NE溢出。6) 4周龄SHR时NGF的神经调节作用减弱。然而，第12周与第6周之间无显著差异

Increased sympathetic nervous activity has been demonstrated in spontaneously hypertensive rats(SHR) and human essential hypertension. Especially, in SHR, increased sympathetic nerve innervation and enhanced norepinephrine(NE) release from vascular tissue have been reported, precise mechanisms of which are not clearly known. To elucidate the contribution of Nerve growth factor(NGF) to the increased sympathetic nervous activity in SHR, the secretion of NGF from cultured vascular smooth muscle cells(VSMCs) was examined and NGF content in various tissues from SHR and control Wistar-Kyoto rats(WKY) was measured. The effects of NGF on NE release from the sympathetic nerve endings were also examined. NGF was purified from mouse submandibular gland according to the Bocchini's method. VSMCs were obtained from the aorta of WKY by explant method. NGF activity was measured by bioassay and NGF content was measured by enzyme immunoassay. Effects of NGF on NE overflow to electrical stimulation were examined using perfused mesenteric artery preparation. 1) Conditioned medium prepared from VSMCs had neurite extention effects on sensory and sympathetic neurons and this effect was blocked by anti-NGF serum. 2) At 3 weeks of age, SHR had a greater NGF content in the spleen, the sciatic nerve, and the mesenteric artery in comparison with WKY.However, these differences were not observed in the adults animals. 3) The expression of NGFmRNA was increased in media of mesenteric artery in in situ hybridization. 4) NGF secretion from cultured VSMCs and mesenteric artery and aorta segment was not significantly difference in in situ hybridization. 5) NGF inhibited NE overflow to electrical stimulation from sympathetic nerve endings in a dose-dependent manner. Inhibition of NE overflow also occurred in the presence of a neuronal uptake blocker, desipramine(5x10-8M). 6) Neuromodulatory effect of NGF was attenuated in 4 week old SHR.However, there were no significant differences between 12 week o