Harrington J T, Hulter H N, Cohen J J, Madias N E
Kidney Int. 1986 Jul;30(1):43-8. doi: 10.1038/ki.1986.148.
Recent in vitro studies of isolated distal nephron segments have demonstrated that mineralocorticoid hormone stimulates H+ secretion by both Na+-dependent and Na+-independent mechanisms, and the Na+-independent acidification mechanism has a greater capacity. These in vitro data suggest that mineralocorticoid administration in vivo might increase renal acid excretion when an augmentation in distal Na+ reabsorption is precluded by rigid restriction of dietary Na+; under these circumstances, virtually all Na+ delivered to the distal nephron is reabsorbed in the basal state. In the present studies, prolonged (12 days) administration of DOC (15 mg/day) was undertaken in both Na+-fed and rigidly Na+-restricted dogs with chronic HCl acidosis. Na+-fed animals responded to DOC administration with a large increment in net acid excretion and complete correction of metabolic acidosis. Marked hypokalemia and significant kaliuresis also occurred. Na+-restricted dogs experienced no changes in renal acid excretion, systemic acid-base equilibrium, plasma [K+] or K+ balance. These results suggest that both renal H+ and K+ excretory responses to prolonged mineralocorticoid hormone administration in vivo are critically dependent on the availability for reabsorption of surplus Na+ within the distal nephron; this requirement is met when the diet, and hence the final urine, contains Na+ but cannot be satisfied when dietary Na+ is rigidly restricted.
近期对离体远端肾单位节段的体外研究表明，盐皮质激素可通过依赖钠和不依赖钠的机制刺激氢离子分泌，且不依赖钠的酸化机制能力更强。这些体外数据提示，当饮食中钠的严格限制阻止远端钠重吸收增加时，体内给予盐皮质激素可能会增加肾酸排泄；在这种情况下，输送到远端肾单位的几乎所有钠在基础状态下都会被重吸收。在本研究中，对患有慢性盐酸酸中毒的钠喂养和严格钠限制的犬，均进行了为期12天的去氧皮质酮（DOC，15毫克/天）给药。钠喂养的动物对DOC给药的反应是净酸排泄大幅增加，代谢性酸中毒完全纠正。还出现了明显的低钾血症和显著的尿钾增多。钠限制的犬在肾酸排泄、全身酸碱平衡、血浆[钾离子]或钾平衡方面没有变化。这些结果表明，体内长期给予盐皮质激素时，肾脏对氢离子和钾离子的排泄反应严重依赖于远端肾单位内多余钠重吸收的可利用性；当饮食以及最终尿液中含有钠时，这一需求能够得到满足，但当饮食中钠被严格限制时则无法满足。
