Miles J M, Nissen S L, Rizza R A, Gerich J E, Haymond M W
Diabetes. 1983 Mar;32(3):197-205. doi: 10.2337/diab.32.3.197.
Ketone bodies have been suggested to have a protein-sparing effect, since infusion of Na-beta-hydroxybutyrate in man decreases plasma alanine concentrations and urinary nitrogen (N) excretion. To test this hypothesis, six normal postabsorptive volunteers were infused with Na-beta-hydroxybutyrate for 3 h. Rates of glucose, leucine carbon, and alanine appearance and disappearance from the plasma space were traced with [3-3H]glucose, L-[6,6,6-2H3]leucine, and [2,3,3,3-2H4]alanine. Rates of leucine N appearance and disappearance and the rate of transfer of leucine N to alanine were assessed with [15N]leucine. During ketone body infusion, plasma alanine decreased (P less than 0.05), whereas plasma leucine increased (P less than 0.05). Rates of alanine appearance increased (5.3 +/- 0.3 to 7.8 +/- 0.6 mumol/kg X min), but the increase in its rate of disappearance was slightly greater, accounting for the decrease in plasma alanine concentration. Leucine N flux and the rate and percent of leucine N transferred to alanine increased, whereas leucine carbon flux was unchanged. To determine the effect of the alkalemia induced by Na-beta-hydroxybutyrate, four additional subjects were infused with NaHCO3. Alkalemia had no effect on leucine N or carbon flux or on the rate of appearance of alanine, but increased the rate of alanine disappearance, resulting in a decrease in the plasma alanine concentration. Since the rate of appearance of leucine carbon was unaltered during the infusion of Na-beta-hydroxybutyrate, it is unlikely that hyperketonemia per se decreases proteolysis in postabsorptive man.
有人提出酮体具有节省蛋白质的作用，因为向人体输注β-羟基丁酸钠会降低血浆丙氨酸浓度和尿氮排泄量。为了验证这一假设，对6名正常的吸收后志愿者输注β-羟基丁酸钠3小时。用[3-³H]葡萄糖、L-[6,6,6-²H₃]亮氨酸和[2,3,3,3-²H₄]丙氨酸追踪血浆中葡萄糖、亮氨酸碳和丙氨酸的出现和消失速率。用[¹⁵N]亮氨酸评估亮氨酸氮的出现和消失速率以及亮氨酸氮向丙氨酸的转移速率。在输注酮体期间，血浆丙氨酸减少（P<0.05），而血浆亮氨酸增加（P<0.05）。丙氨酸的出现速率增加（从5.3±0.3增至7.8±0.6μmol/kg·min），但其消失速率的增加略大，这解释了血浆丙氨酸浓度的降低。亮氨酸氮通量以及亮氨酸氮转移至丙氨酸的速率和百分比增加，而亮氨酸碳通量未改变。为了确定β-羟基丁酸钠引起的碱血症的影响，另外4名受试者输注了碳酸氢钠。碱血症对亮氨酸氮或碳通量以及丙氨酸的出现速率没有影响，但增加了丙氨酸的消失速率，导致血浆丙氨酸浓度降低。由于在输注β-羟基丁酸钠期间亮氨酸碳的出现速率未改变，高酮血症本身不太可能降低吸收后人体的蛋白质分解代谢。
