Abstract

Measuring tissue calcium (Ca²⁺) content, Ca²⁺ absorption, plasma, urinary and fecal Ca²⁺ levels during and after hypokinesia (HK) and Ca²⁺ supplementation was the aim of this study showing if Ca²⁺ deposition could be depressed significantly more with than without Ca²⁺ supplementation, contributing to significantly higher Ca²⁺ losses from the body with tissue Ca²⁺ depletion. Studies were conducted on 408 13-week-old male Wistar rats (370 – 390 g) during nine days pre-HK, 98 days HK and 15 days post-HK periods. Rats were equally divided into four groups: unsupplemented vivarium control rats (UVCR), unsupplemented hypokinetic rats (UHKR), supplemented vivarium control rats (SVCR) and supplemented hypokinetic rats (SHKR). Hypokinetic rats were kept in small individual cages for 98 days which restricted their movements in all directions without hindering food and water intake. Control rats were housed in individual cages for 98 days under vivarium control conditions. All SVCR and SHKR consumed 2.8 mmol calcium lactate per day. Calcium absorption, intact parathyroid hormone (iPTH) levels, and Ca²⁺ levels in muscle, bone, plasma, urine and feces, did not change in SVCR and UVCR compared with their baseline values. During HK, Ca²⁺ absorption, plasma iPTH levels and muscle and bone, Ca²⁺ content decreased significantly (p < 0.05) with time, while plasma Ca²⁺ levels, fecal and urinary Ca²⁺ loss increased significantly (p < 0.05) with time in SHKR and UHKR, compared with their pre-HK values and their respective vivarium controls (SVCR and UVCR). During the initial nine days of post-HK, Ca²⁺ absorption increased significantly (p < 0.05), and plasma, urinary and fecal Ca²⁺ levels decreased significantly (p < 0.05), while muscle and bone Ca²⁺ content and plasma iPTH levels remained significantly (p < 0.05) depressed in SHKR and UHKR compared to their respective vivarium control values; by the 15th day of post-HK period, the measured parameters approached the pre-HK values. During HK and post-HK, Ca²⁺ absorption, iPTH levels and Ca²⁺ levels in muscle, bone, plasma, urine and feces changed significantly (p < 0.05) more with time in SHKR than UHKR. Significantly greater Ca²⁺ loss with significantly lower tissue Ca²⁺ content in SHKR than UHKR showed that Ca²⁺ deposition was decreased more with than without Ca²⁺ supplementation. It was concluded that dissociation between decreased tissue Ca²⁺ content and increased Ca²⁺ losses showed decreased Ca²⁺ deposition as the main mechanism for tissue Ca²⁺ depletion during HK.

Author Details

Authors

• Y.G. Zorbas¹
• V.A. Deogenov¹
• V.J. Kakuris²
• V.L. Yerullis¹,²

Departments

• ¹ European Foundation of Environmental Sciences, and
• ² Institute of Occupational Physiology, Athens, Greece

Address

Dr. V.A. Deogenov
European Foundation of Environmental Sciences, Odos Kerasundos 2, GR-162 32 Athens, Greece
Email: [email protected]

Citation