Calcium administration increases calcium-binding protein regucalcin concentration in the liver of rats

The alteration of regucalcin concentrations in the liver and serum of rats administered orally calcium is investigated. Rats received a single oral administration of calcium chloride solution (25, 50 and 75 mg Ca/100 g body weight). The administration of calcium (50 mg/100 g) produced a significant increase in liver regucalcin concentration between 30 and 180 min after the administration, while serum regucalcin concentration was not altered appreciably. The effect of calcium administration increasing liver regucalcin concentration was also seen with the dose of 25 mg/100 g. When liver cytosol prepared from normal rats was incubated for 6 h in the presence of 10 M Ca²⁺, the cytosolic regucalcin concentration at 3 and 6 h of incubation was decreased about 20% (p<0.05) as compared with the value at zero time point, indicating that the presence of Ca²⁺ does not inhibit the decomposition of liver cytosolic regucalcin. Moreover, serum regucalcin concentration was not significantly altered by the incubation for 6 h at 37°C, indicating a stability of regucalcin in rat serum. This suggests that the calcium administration-induced in liver regucalcin concentration is not based on the inhibition of regucalcin release from liver to serum. The present study demonstrates that regucalcin in the liver is clearly increased by calcium administration, presumably due to stimulating the protein synthesis.