Calcium absorption measurements in normal subjects in determining calcium deposition during prolonged hypokinesia and with and without calcium loading.

Measuring calcium (Ca) absorption, Ca balance and Ca level in serum,feces and urine during HK (hypokinesia) with and without Ca loading, the aim of this study was to disclose if prolonged HK could reduce Ca deposition more with or without Ca load contributing to greater Ca imbalance. Studies were conducted during 30-days pre-HK and 364-days HK. Forty male normal volunteers 23.7+/-6.0 years of age were chosen as subjects. They were divided into four groups: unloaded active control subjects (UACS), unloaded hypokinetic subjects (UHKS), loaded active control subjects (LACS), loaded hypokinetic subjects (LHKS). All hypokinetic subjects were walking average distances of 0.5+/-0.2 km day(-1), and active control subjects were running average distances of 6.6+/-1.2 km day(-1). LACS and LHKS were loaded with 1.3 mmol calcium lactate/kg body wt. Before Ca load, fecal Ca loss, urinary Ca and phosphate (P) losses, Ca imbalance, serum ionized calcium (CaI), P and total Ca (Ca(t)) levels increased significantly. (P < 0.05) with time, and serum intact parathyroid hormone (iPTH), 1.25 dihydroxyvitamin D (1.25(OH)2D3) levels and Ca absorption, decreased significantly (P < 0.05) with time in LHKS and UHKS compared with their pre-HK values and their respective active controls (LACS and UACS). After Ca load, however, Ca absorption, serum iPTH and 1.25 (OH)2D3 levels decreased significantly (P < 0.05) more with time, while fecal Ca loss, urinary Ca and P excretion and Ca imbalance increased significantly (P < 0.05) more with time in LHKS than UHKS. Conversely, before and after Ca load, fecal Ca excretion, urinary P and Ca loss, serum CaI, P, Ca, iPTH and 1.25 (OH)2D3 levels, Ca absorption and Ca balance did not change in LACS and UACS compared with their pre-HK values. The greater Ca losses with than without Ca load have shown that the more Ca is consumed the more Ca is eliminated during HK and Ca imbalance. The significant increase of Ca loss with Ca imbalance demonstrated reduced Ca deposition. Dissociation between Ca loss and Ca imbalance demonstrated reduced Ca deposition as the mechanism of Ca imbalance development during HK.