Chobanian M C, Julin C M, Molteni K H, Brazy P C
Department of Pediatrics, University of Wisconsin School of Medicine, Madison 53792.
Am J Physiol. 1992 May;262(5 Pt 2):F878-84. doi: 10.1152/ajprenal.1992.262.5.F878.
To determine whether growth hormone (GH) directly affects ammoniagenesis in the renal proximal tubule, ammonia production was measured in suspensions of isolated canine renal proximal tubule segments (IPTs) incubated with 2.5 mM L-glutamine and varying concentrations of human growth hormone (hGH). Ammonia production from IPTs significantly increased by nearly threefold in the presence of hGH (10(-6) M) at 60 min. This increase was dose dependent, with as little as 10(-9) M hGH significantly stimulating ammonia production. In addition, hGH enhanced glucose production when lactate, alanine, and succinate replaced L-glutamine as substrate. hGH significantly stimulated ammonia production when IPTs were incubated at alkalotic and neutral pH. The effect of hGH was lost at acidic pH. When hGH was added to IPTs incubated under Na(+)-equilibrated conditions, ammonia production was not different from control. hGH stimulated ouabain-sensitive Na(+)-K(+)-adenosinetriphosphatase (ATPase) activity by 8.1 +/- 1.1% in basolateral membranes isolated from IPTs. hGH stimulation of proximal tubule ammonia production from L-glutamine occurs at physiological concentrations of hGH and when the extracellular-to-intracellular Na+ gradient favors L-glutamine transport. This effect is associated with an increase in basolateral Na(+)-K(+)-ATPase activity. The data suggest a role for hGH in the regulation of renal acid-base metabolism under physiological conditions in which increased net acid excretion is important.
为了确定生长激素（GH）是否直接影响肾近端小管中的氨生成，在分离的犬肾近端小管节段（IPTs）悬浮液中加入2.5 mM L-谷氨酰胺和不同浓度的人生长激素（hGH），并测定氨的生成量。在60分钟时，hGH（10^(-6) M）存在的情况下，IPTs产生的氨显著增加了近三倍。这种增加呈剂量依赖性，低至10^(-9) M的hGH就能显著刺激氨的生成。此外，当乳酸、丙氨酸和琥珀酸替代L-谷氨酰胺作为底物时，hGH增强了葡萄糖的生成。当IPTs在碱性和中性pH条件下孵育时，hGH显著刺激氨的生成。在酸性pH条件下，hGH的作用消失。当hGH添加到在Na(+)平衡条件下孵育的IPTs中时，氨的生成与对照无差异。hGH刺激从IPTs分离的基底外侧膜中哇巴因敏感的Na(+)-K(+)-三磷酸腺苷酶（ATPase）活性增加8.1±1.1%。hGH在生理浓度下以及细胞外与细胞内Na+梯度有利于L-谷氨酰胺转运时，刺激近端小管从L-谷氨酰胺生成氨。这种作用与基底外侧Na(+)-K(+)-ATPase活性增加有关。数据表明，在净酸排泄增加很重要的生理条件下，hGH在肾酸碱代谢调节中发挥作用。
