ABSTRACT
In order to investigate fractionation of calcium (Ca) isotopes in vertebrates as a diagnostic tool to detect Ca metabolism dysfunction we analyzed the Ca isotopic composition (δ44/40Ca = [(44Ca/40Ca)sample/(44Ca/40Ca)reference]−1) of diet, faeces, blood, bones and urine from Göttingen minipigs, an animal model for human physiology. Samples of three groups were investigated: 1. control group (Con), 2. group with glucocorticosteroid induced osteoporosis (GIO) and 3. group with Ca and vitamin D deficiency induced osteomalacia (−CaD). In contrast to Con and GIO whose average δ44/40Cafaeces values (0.39 ± 0.13‰ and 0.28 ± 0.08‰, respectively) tend to be lower than their diet (0.47 ± 0.02‰), δ44/40Cafaeces of −CaD (−0.27 ± 0.21‰) was significantly lower than their δ44/40Cadiet (0.37 ± 0.03‰), but also lower than δ44/40Cafaeces of Con and GIO. We suggest that the low δ44/40Cafaeces of −CaD might be due to the contribution of isotopically light Ca from gastrointestinal fluids during gut passage. Assuming that this endogenous Ca source is a common physiologic feature, a fractionation during Ca absorption is also required for explaining δ44/40Cafaeces of Con and GIO. The δ44/40Caurine of all groups are high (>2.0‰) reflecting preferential renal reabsorption of light Ca isotopes. In Göttingen minipigs we found a Ca isotope fractionation between blood and bones (Δ44/40Cablood-bone) of 0.68 ± 0.15‰.
Acknowledgements
We thank A. Kolevica for lab support and K. Gonda for her analytical assistance (sample digestions and chemical Ca analyses). J. Kunze, H. Fischer and D. Siewertsen are acknowledged for their thoroughly performed animal care. We are thankful for the constructive and helpful input given by two anonymous reviewers. The editor is thanked for the handling of the manuscript.
Disclosure statement
No potential conflict of interest was reported by the authors.