Chobanian M C, Hammerman M R
Department of pediatrics, University of Wisconsin, Madison 53792.
Am J Physiol. 1988 Nov;255(5 Pt 2):F847-52. doi: 10.1152/ajprenal.1988.255.5.F847.
To determine whether parathyroid hormone (PTH) affects ammoniagenesis in renal proximal tubule, we measured ammonia production in suspensions of canine renal proximal tubular segments incubated with 10 mM L-glutamine in the absence or presence of 10(-7) M PTH. Productions of ammonia were linear functions of time for 120 min and averaged 231 +/- 55 and 311 +/- 67 mumol ammonia/g protein in the absence and presence of PTH, respectively. When measured over the range of 10(-11)-10(-7) M PTH, half-maximal stimulation of ammonia production occurred between 10(-10) and 10(-9) M PTH. Maximal production of ammonia was observed at 10(-8) M PTH. Incubation of proximal tubular segments with PTH increased levels of adenosine 3',5'-cyclic monophosphate (cAMP) in vitro. Ammonia production was significantly enhanced by incubation of segments with the cAMP analogue, 8-bromoadenosine 3',5'-cyclic monophosphate. PTH also increased ammonia production in segments incubated with 1 mM L-glutamine. We conclude that PTH stimulates ammonia production in canine renal proximal tubular segments. This effect appears to be mediated, at least in part, through cAMP in vitro. Such stimulation could reflect a direct action of PTH on the proximal tubule to enhance ammoniagenesis in vivo.
为了确定甲状旁腺激素（PTH）是否影响肾近端小管中的氨生成，我们在不存在或存在10⁻⁷ M PTH的情况下，测量了用10 mM L-谷氨酰胺孵育的犬肾近端小管节段悬浮液中的氨生成。在不存在和存在PTH的情况下，氨生成在120分钟内是时间的线性函数，平均分别为231±55和311±67 μmol氨/克蛋白质。当在10⁻¹¹ - 10⁻⁷ M PTH范围内测量时，氨生成的半数最大刺激发生在10⁻¹⁰和10⁻⁹ M PTH之间。在10⁻⁸ M PTH时观察到氨的最大生成量。在体外，用PTH孵育近端小管节段会增加3',5'-环磷酸腺苷（cAMP）的水平。用cAMP类似物8-溴-3',5'-环磷酸腺苷孵育节段可显著增强氨生成。PTH还增加了用1 mM L-谷氨酰胺孵育的节段中的氨生成。我们得出结论，PTH刺激犬肾近端小管节段中的氨生成。这种作用在体外似乎至少部分是通过cAMP介导的。这种刺激可能反映了PTH对近端小管的直接作用，以增强体内的氨生成。
