The role of the parathyroids for the adaptation to a low calcium intake. 4. The long-term effect of parathyroidectomy on the adaptation to a low calcium intake in adult rats with special reference to calcium metabolism.
One-year-old selectively parathyroidectomized rats showed, on a normal dietary intake of calcium, phosphorus and vitamin D, a reduction in plasma calcium to below 4.1 mEq./1 in 86 per cent and on restricted calcium intake in 100 per cent. On the normal level of dietary calcium, normalization of plasma calcium occurred 17 per cent within 8 weeks and in another 40 per cent between the 8th and 27th week of observation while on the low level only 10 per cent of the animals normalized their plasma calcium and first after the long-term period of observation. This was most probably accomplished by successively restored parathyroid activity from aberrant parathyroid tissue as deducted from data regarding the metabolism of calcium, magnesium and inorganic phosphate. Adaptation, viz. normalization of plasma calcium, was brought about by mobilization of skeletal calcium with resulting osteoporosis, as reported in our previous study on the same animals. Intestinal net absorption of calcium showed no significant difference between normocalcemic normophosphatemic intact and hypocalcemic hyperphosphatemic parathyroidectomized animals at the respective level of dietary calcium. Thus, parathyroidectomized animals with persistently reduced plasma calcium showed a normal adaptory increase in intestinal calcium absorption upon chronically restricted calcium intake. In the discussion of the regulation of this adaptory system the possible effects of the plasma concentrations of both calcium and inorganic phosphate upon the intracellular Ca22+concentration in the kidney tubules must be considered. Plasma magnesium did not appear to have a primary influence. Intestinal absorption of inorganic phosphate was not dependent upon the presence of the parathyroids but followed that of calcium suggesting a regulation by the action of 1,25-dihydroxycholecalciferol.
D000222:Adaptation, Physiological; D000818:Animals; D002118:Calcium / Q000097:blood / Q000378:metabolism*; D002136:Calcium, Dietary; D004100:Dihydroxycholecalciferols / Q000378:metabolism; D005243:Feces / Q000032:analysis; D007408:Intestinal Absorption; D008274:Magnesium / Q000097:blood / Q000378:metabolism / Q000652:urine; D008297:Male; D010024:Osteoporosis; D010280:Parathyroid Glands / Q000378:metabolism / Q000502:physiology*; D010710:Phosphates / Q000097:blood / Q000378:metabolism / Q000652:urine; D051381:Rats; D013997:Time Factors
D002136:Calcium, Dietary; D004100:Dihydroxycholecalciferols; D010710:Phosphates; D008274:Magnesium; D002118:Calcium