THE MECHANISM OF AGE-RELATED CHANGES IN THE RELEASE OF NITRIC OXIDE.

冠状动脉疾病引起的心血管疾病的发生率随着年龄的增长而增加。血管内皮细胞在调节血管张力和维持心血管功能方面起着重要作用。我们已证实血管紧张素II和内皮素-1等缩血管多肽能刺激幼年大鼠冠状动脉内NO的释放，但在老年大鼠冠状动脉中NO的产生受到抑制。这种NO生成的减少可能是老年大鼠血管收缩作用增强的原因之一。相反，血管紧张剂对老年大鼠PGI_2释放的刺激作用比青年大鼠大得多。衰老内皮细胞产生PGI_2可能是NO生成减少的一种代偿机制。为了阐明增龄相关NO和PGI_2释放的变化机制，我们检测了NO合成相关酶和PGI_2受体表达的增龄性变化，以揭示其调节PGI_2生成的机制。动脉和心脏分别取自3月龄和27月龄的Fischer 344只大鼠。心脏在37℃恒压灌流(75cmH2O)。用流量计测量冠脉流量的变化。用EIA法检测冠脉流出液中6-酮-前列腺素F1α和GT；用实时荧光定量聚合酶链式反应和Western印迹分析检测冠脉流出液中前列腺素I2受体、一氧化氮和前列腺素I合成酶及环氧合酶-1(COX-1)的表达变化。老年大鼠流出液中PGI_2的释放量大于青年大鼠。PGI2受体的数量与年龄无相关性。COX-1和PGI合酶在老年大鼠的表达增加。这种COX-1和PGI合酶的增加可能是老年大鼠冠状动脉产生PGI_2增加的原因之一。一氧化氮合酶和精氨酸转运蛋白的表达是否会随着年龄的增长而改变，目前尚不清楚。

The incidence of cardiovascular disorder due to coronary artery disease increases with advansing age. Endothelium plays an important role in regulating vascular tone and in maintaining the cardiovascular function. We previously demonstrated that several vasoconstricting peptides such as angiotensin II and endothelin-1 stimulated the release of NO in the coronary artery of young rat, but the production was attenuated in the aged rat. This impaired production of NO may contribute to the greater constrictor effect of the vasoconstrictors in the aged rat. In contrast, the vasoconstrictors stimulated the release of PGI_2 to a much greater extent in aged rats than in young rats. It might be possible that aged endothelial cells could produce PGI_2 as a compensation-mechanism for reduced production of NO.To elucidate the mechanism of age-related changes in the release of NO and PGI_2, We examined the age-related changes in the expression of enzymes responsible for the synthesis of NO and PGI_2 and PGI_2 receptors to reveal the mechanism of regulation of PGI_2 production. Aorta and hearts were isolated from 3- and 27- months old Fischer 344 rats. Hearts were perfused with constant pressure (75 cmH_2O) at 37℃. Changes in the coronary flow were measured with a flow meter. 6-keto-PGF_<1α> in the coronary effluent was measured with EIA.Changes in the expression of PGI_2 receptors, NO and PGI synthase and cyclooxygenase-1 (COX-1) were quantified by real-time PCR and Western blot analysis. Release of PGI_2 into the effluent was greater in the aged rat than young rat. There was no age-related difference in the amount of PGI_2 receptor. Expression of COX-1 and PGI synthase was increased in the aged rat. These increases in COX-1 and PGI synthase may be responsible for the increased production of PGI_2 in the aged rat coronary artery. It is not yet clarified whether the expressions of NO syntase and arginine transportor change with aging.