Mitchell Brett M, Dorrance Anne M, Webb R Clinton
Department of Physiology CL-3162, Medical College of Georgia, 1120 15th Street, Augusta, GA 30912, USA.
Am J Physiol Heart Circ Physiol. 2003 Nov;285(5):H2165-70. doi: 10.1152/ajpheart.00253.2003. Epub 2003 Jul 10.
GTP cyclohydrolase 1 is the rate-limiting enzyme in production of tetrahydrobiopterin, a necessary cofactor for endothelial nitric oxide synthase. We tested the hypothesis that inhibition of tetrahydrobiopterin synthesis impairs endothelium-dependent relaxation and increase blood pressure in rats. 2,4-Diamino-6-hydroxypyrimidine (DAHP), a GTP cyclohydrolase 1 inhibitor, was given in drinking water (approximately 120 mg.kg(-1).day(-1)) to male Sprague-Dawley rats for 3 days. Systolic blood pressures were measured (tail-cuff procedure) for 3 days before and each day during DAHP treatment. Blood pressure was significantly increased after DAHP treatment (122 +/- 2 vs. 154 +/- 3 mmHg before and after DAHP, respectively; P < 0.05). Endothelium-intact aortic segments from pentobarbital sodium-anesthetized rats were isolated and hung in organ chambers for measurement of isometric force generation. Aortas from DAHP-treated rats exhibited a decreased maximal relaxation to ACh compared with controls [% relaxation from phenylephrine (10-7 M)-induced contraction: DAHP 57 +/- 6% vs. control 79 +/- 4%; P < 0.05]. Relaxation responses to A-23187 were also decreased in aortas from DAHP-treated rats compared with controls. Incubation with sepiapterin (10-4 M, 1 h), which produces tetrahydrobiopterin via a salvage pathway, restored relaxation to ACh in aortas from DAHP-treated rats. Superoxide dismutase significantly increased ACh-induced relaxation in aortas from DAHP-treated rats, whereas catalase had no effect. Endothelium-independent relaxation to sodium nitroprusside in aortas from DAHP-treated rats was not different from control rats; however, nitric oxide synthase inhibition increased sensitivity to sodium nitroprusside in aortas from DAHP-treated rats. These results support the hypothesis that GTP cyclohydrolase 1 inhibition decreases relaxation and increases blood pressure in rats.
鸟苷三磷酸环化水解酶1是四氢生物蝶呤生成过程中的限速酶，四氢生物蝶呤是内皮型一氧化氮合酶必需的辅助因子。我们检验了以下假说：抑制四氢生物蝶呤合成会损害大鼠的内皮依赖性舒张功能并升高血压。将鸟苷三磷酸环化水解酶1抑制剂2,4-二氨基-6-羟基嘧啶（DAHP）加入雄性Sprague-Dawley大鼠的饮用水中（约120 mg·kg⁻¹·d⁻¹），持续3天。在给予DAHP治疗前3天以及治疗期间每天，采用尾套法测量收缩压。DAHP治疗后血压显著升高（DAHP治疗前后收缩压分别为122±2 mmHg和154±3 mmHg；P<0.05）。从戊巴比妥钠麻醉的大鼠中分离出完整内皮的主动脉节段，悬挂于器官浴槽中以测量等长力的产生。与对照组相比，DAHP处理大鼠的主动脉对乙酰胆碱的最大舒张反应降低[去氧肾上腺素（10⁻⁷ M）诱导收缩后的舒张百分比：DAHP组为57±6%，对照组为79±4%；P<0.05]。与对照组相比，DAHP处理大鼠的主动脉对A-23187的舒张反应也降低。用蝶呤（10⁻⁴ M，1小时）孵育，蝶呤通过补救途径生成四氢生物蝶呤，可使DAHP处理大鼠主动脉对乙酰胆碱的舒张功能恢复。超氧化物歧化酶显著增加了DAHP处理大鼠主动脉对乙酰胆碱诱导的舒张反应，而过氧化氢酶则无此作用。DAHP处理大鼠主动脉对硝普钠的非内皮依赖性舒张与对照大鼠无差异；然而，抑制一氧化氮合酶会增加DAHP处理大鼠主动脉对硝普钠的敏感性。这些结果支持了以下假说：抑制鸟苷三磷酸环化水解酶1会降低大鼠的舒张功能并升高血压。
