The bioavailability of calcium in spinach and calcium-oxalate to calcium-deficient rats.
We estimated the utilization of calcium in spinach and calcium-oxalate to calcium-deficient rats, and the effect of oxalic acid on absorption of dietary calcium by using calcium-deficient rats. The body weight gain of the calcium-deficient rats for 8 days receiving a calcium-deficient diet supplemented with raw-powdered spinach (R-sp), boiled-powdered spinach (B-sp), or calcium-oxalate (Ca-ox), and a control diet supplemented with oxalic acid (OX-C) were 4.8, 2.8, 4.9, and 5.1 g, respectively. The calcium content in the liver and kidney of the rats receiving R-sp, B-sp, Ca-ox, and OX-C diets significantly increased as compared with the calcium-deficient rats. Significant differences in the liver calcium levels were not observed among the rats receiving various additional diets, though the content in the kidneys of the rats receiving R-sp, B-sp, Ca-ox, and OX-C diets were 28.0, 21.5, 0.11, and 0.59 mg, respectively. An especially large amount of calcium was accumulated in the kidneys of the rats receiving R-sp and B-sp diets. The calcium concentration in the serum of the rats receiving Ca-ox and OX-C diets was higher than the calcium concentration in the serum of the R-sp, B-sp, and calcium-deficient rats. The calcium content in the left tibiae of the rats receiving Ca-ox and OX-C diets was higher than that of the rats receiving R-sp and B-sp diets. The breaking force of the right tibiae of the rats was highest in the OX-C group, and higher in the R-sp and Ca-ox groups than the breaking force of the right tibiae of the rats fed on B-sp diet. The alkaline phosphatase activity in the small intestines of the rats rose in the order of the R-sp, B-sp, and Ca-ox groups, although significant differences of the activity were not observed between the Ca-ox and the OX-C groups. The calcium retention of the rats receiving the calcium-deficient, R-sp, B-sp, Ca-ox, and OX-C diets was -18.5, 35.2, 25.6, 41.6, and 45.8%, respectively. About 35% of the calcium in the spinach was absorbed by the calcium-deficient rats, and oxalic acid depressed the calcium absorption in the rats.
Kikunaga
S
S
Faculty of Home Economics, Notre Dame Seishin University, Okayama, Japan.
Arimori
M
M
Takahashi
M
M
D000042:Absorption; D000818:Animals; D001682:Biological Availability; D001842:Bone and Bones / Q000503:physiopathology; D002118:Calcium / Q000097:blood / Q000172:deficiency / Q000493:pharmacokinetics*; D002129:Calcium Oxalate / Q000493:pharmacokinetics*; D007668:Kidney / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008297:Male; D009929:Organ Size; D010070:Oxalates / Q000494:pharmacology; D019815:Oxalic Acid; D051381:Rats; D011919:Rats, Inbred Strains; D013718:Tensile Strength; D013977:Tibia; D014675:Vegetables; D014886:Weaning
D010070:Oxalates; D002129:Calcium Oxalate; D019815:Oxalic Acid; D002118:Calcium