LeBlanc A, Schneider V, Spector E, Evans H, Rowe R, Lane H, Demers L, Lipton A
Department of Medicine, Baylor College of Medicine, Houston, TX, USA.
Bone. 1995 Apr;16(4 Suppl):301S-304S. doi: 10.1016/8756-3282(94)00045-2.
Negative calcium balance is a known consequence of bed rest, and is manifested in elevated urine and fecal calcium (Ca). Elevated fecal Ca can result from either decreased absorption, increased endogenous fecal excretion, or both. We measured the Ca absorption and endogenous fecal excretion in eight healthy male volunteers before and during 4 months of bed rest. Dual isotope (n = 6) or single isotope (n = 2) methods in conjunction with Ca balance were used to calculate true and net Ca absorption and endogenous fecal excretion. Stool Ca increased from 797 mg/day (mean intake 991 mg/day) to 911 mg/day during bed rest, whereas urine Ca excretion increased from 174 to 241 mg/day. True Ca absorption decreased from 31 +/- 7% of Ca intake pre-bed rest to 24 +/- 2% during bed rest, (p < 0.05) and returned toward pre-bed rest values within 5-6 weeks following reambulation. Endogenous fecal excretion did not change significantly, and therefore, most of the increased fecal Ca resulted from changes in absorption. However, in one individual, endogenous fecal Ca excretion was the major contributor to Ca loss. Ionized Ca and pyridinium crosslinks increased and 1,25(OH)2 vitamin D decreased during bed rest, similar to the decrease in Ca absorption; parathyroid hormone (PTH), calcitonin, serum albumin, phosphorus, and total serum Ca were unchanged. Although alkaline phosphatase, osteocalcin, and PTH were unchanged during bed rest, they were elevated during reambulation. These changes accompanied by increased Ca absorption and balance and decreased ionized and total serum Ca suggest a rebound in bone formation following immobilization.
负钙平衡是卧床休息的一个已知后果，表现为尿钙和粪钙升高。粪钙升高可能是由于吸收减少、内源性粪钙排泄增加或两者兼而有之。我们测量了8名健康男性志愿者在卧床休息4个月前后的钙吸收和内源性粪钙排泄。采用双同位素（n = 6）或单同位素（n = 2）方法结合钙平衡来计算真实和净钙吸收以及内源性粪钙排泄。卧床休息期间，粪便钙从797毫克/天（平均摄入量991毫克/天）增加到911毫克/天，而尿钙排泄从174毫克/天增加到241毫克/天。真实钙吸收从卧床休息前占钙摄入量的31±7%降至卧床休息期间的24±2%（p < 0.05），并在重新行走后5 - 6周内恢复到卧床休息前的值。内源性粪钙排泄没有显著变化，因此，粪便钙增加主要是由于吸收变化。然而，在一个个体中，内源性粪钙排泄是钙流失的主要原因。卧床休息期间，离子钙和吡啶交联物增加，1,25(OH)2维生素D减少，与钙吸收减少相似；甲状旁腺激素（PTH）、降钙素、血清白蛋白、磷和总血清钙没有变化。尽管卧床休息期间碱性磷酸酶、骨钙素和PTH没有变化，但在重新行走期间它们升高。这些变化伴随着钙吸收和平衡增加以及离子钙和总血清钙减少，提示固定后骨形成出现反弹。
