Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio.
Am J Physiol Renal Physiol. 2021 Sep 1;321(3):F369-F377. doi: 10.1152/ajprenal.00124.2021. Epub 2021 Jul 26.
Dahl salt-sensitive (SS) rat kidneys produce less nitric oxide (NO) than those of salt-resistant (SR) rats. Thick ascending limb (TAL) NO synthase 3 (NOS3) is a major source of renal NO, and luminal flow enhances its activity. We hypothesized that flow-induced NO is reduced in TALs from SS rats primarily due to NOS uncoupling and diminished NOS3 expression rather than scavenging. Rats were fed normal-salt (NS) or high-salt (HS) diets. We measured flow-induced NO and superoxide in perfused TALs and performed Western blots of renal outer medullas. For rats on NS, flow-induced NO was 35 ± 6 arbitrary units (AU)/min in TALs from SR rats but only 11 ± 2 AU/min in TALs from SS ( < 0.008). The superoxide scavenger tempol decreased the difference in flow-induced NO between strains by about 36% ( < 0.020). The NOS inhibitor -nitro-l-arginine methyl ester (l-NAME) decreased flow-induced superoxide by 36 ± 8% in TALs from SS rats ( < 0.02) but had no effect in TALs from SR rats. NOS3 expression was not different between strains on NS. For rats on HS, the difference in flow-induced NO between strains was enhanced (SR rats: 44 ± 10 vs. SS: 9 ± 2 AU/min, < 0.005). Tempol decreased the difference in flow-induced NO between strains by about 37% ( < 0.012). l-NAME did not significantly reduce flow-induced superoxide in either strain. HS increased NOS3 expression in TALs from SR rats but not in TALs from SS rats ( < 0.003). We conclude that ) on NS, flow-induced NO is diminished in TALs from SS rats mainly due to NOS3 uncoupling such that it produces superoxide and ) on HS, the difference is enhanced due to failure of TALs from SS rats to increase NOS3 expression. The Dahl rat has been used extensively to study the causes and effects of salt-sensitive hypertension. Our study suggests that more complex processes other than simple scavenging of nitric oxide (NO) by superoxide lead to less NO production in thick ascending limbs of the Dahl salt-sensitive rat. The predominant mechanism involved depends on dietary salt. Impaired flow-induced NO production in thick ascending limbs most likely contributes to the Na retention associated with salt-sensitive hypertension.
达勒盐敏感（SS）大鼠肾脏产生的一氧化氮（NO）比盐抵抗（SR）大鼠少。厚升支（TAL）NO 合酶 3（NOS3）是肾脏 NO 的主要来源，管腔流增强其活性。我们假设 SS 大鼠 TAL 中的诱导型 NO 减少主要是由于 NOS 解偶联和 NOS3 表达减少而不是清除。大鼠给予正常盐（NS）或高盐（HS）饮食。我们测量了灌注 TAL 中的诱导型 NO 和超氧化物，并对肾外髓质进行了 Western 印迹分析。对于 NS 饮食的大鼠，SR 大鼠 TAL 中的诱导型 NO 为 35±6 个任意单位（AU）/min，但 SS 大鼠 TAL 中仅为 11±2 AU/min（<0.008）。超氧化物清除剂tempol 使两株大鼠之间的诱导型 NO 差异减少了约 36%（<0.020）。NOS 抑制剂 -硝基-L-精氨酸甲酯（l-NAME）使 SS 大鼠 TAL 中的诱导型超氧化物减少了 36±8%（<0.02），但对 SR 大鼠 TAL 没有影响。NS 饮食下，两株大鼠的 NOS3 表达无差异。对于 HS 饮食的大鼠，两株大鼠之间的诱导型 NO 差异增加（SR 大鼠：44±10 对 SS：9±2 AU/min，<0.005）。Tempol 使两株大鼠之间的诱导型 NO 差异减少了约 37%（<0.012）。l-NAME 并未显著减少两株大鼠的诱导型超氧化物。HS 增加了 SR 大鼠 TAL 中的 NOS3 表达，但未增加 SS 大鼠 TAL 中的 NOS3 表达（<0.003）。我们得出结论，）在 NS 时，SS 大鼠 TAL 中的诱导型 NO 减少主要是由于 NOS3 解偶联，导致其产生超氧化物，）在 HS 时，差异增强是由于 SS 大鼠 TAL 无法增加 NOS3 表达所致。达勒大鼠被广泛用于研究盐敏感性高血压的原因和影响。我们的研究表明，与超氧化物对一氧化氮（NO）的简单清除相比，导致达勒盐敏感大鼠厚升支中 NO 产生减少的过程更为复杂。涉及的主要机制取决于饮食中的盐。厚升支中诱导型 NO 产生受损很可能导致与盐敏感性高血压相关的钠潴留。
