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

自发性高血压大鼠(SHR)和人类高血压患者的交感神经活动增强。特别是在SHR中，交感神经支配增加和血管组织去甲肾上腺素(NE)释放增加已有报道，但其确切机制尚不清楚。为探讨神经生长因子(NGF)在自发性高血压大鼠(SHR)交感神经活动增强中的作用，观察了培养的血管平滑肌细胞(VSMCs)分泌NGF的情况，并测定了SHR和正常WKY大鼠(WKY)各组织中NGF的含量。观察神经生长因子对交感神经末梢去甲肾上腺素释放的影响。采用Bocchini法从小鼠颌下腺中分离纯化神经生长因子。采用组织块法从WKY大鼠的主动脉中获取VSMCs。用生物法测定NGF活性，用酶免疫法测定NGF含量。采用肠系膜动脉灌流法制备大鼠肠系膜动脉，观察NGF对电刺激引起的去甲肾上腺素外溢的影响。1)VSMCs条件培养液对感觉神经元和交感神经元有突起伸展作用，该作用可被抗NGF血清阻断。2)3周龄时，SHR的脾、坐骨神经和肠系膜动脉中的NGF含量高于WKY，但在成年动物中未观察到这些差异。3)原位杂交显示肠系膜动脉中膜神经生长因子基因表达增强。4)原位杂交显示培养的VSMCs与肠系膜动脉和主动脉段分泌的NGF无显著差异。5)NGF以剂量依赖的方式抑制交感神经末梢对去甲肾上腺素的溢出。神经元摄取阻断剂地昔帕明(5×10~(-8)M)也可抑制去甲肾上腺素溢出。6)神经生长因子的神经调节作用在4周龄时减弱，但在12周龄时无显著差异。

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