Abstract
Summary
The relationships of parathyroid hormone and calcitonin to plasma and liver phosphate concentrations were studied in rats. While parathyroid hormone affected plasma phosphate levels, it did not control the daily fluctuations in rats adapted to standard feeding and light conditions. The endogenous presence of this hormone did prevent the additional rise in plasma phosphate concentrations which occurs in its absence following an overnight fast.
Inorganic phosphate concentrations of liver were always higher than plasma phosphate and were surprisingly constant despite almost fourfold variation in plasma concentrations. They remained relatively constant even 3 weeks after the rats were placed on a low phosphate diet and after extended thy-roparathyroidectomy. Only minor differences were seen in liver inorganic phosphate levels in fed and fasted rats. It is concluded that this phosphate pool is under some type of homeostatic control.
The organically bound phosphate in the acid-soluble pool of liver increases rapidly after feeding, decreasing just as rapidly on fasting. These changes were not influenced by the phosphate level of plasma nor the presence or absence of either endogenous parathyroid hormone or calcitonin and occurred while the rats were on a low phosphate diet. It is concluded that neither parathyroid hormone nor calcitonin directly affects these two acid soluble phosphate pools in liver.
The authors appreciate the fine technical assistance of Ms. Dorothy B. Raneri and Ms. Blanche P. Hollo-way. Thanks are expressed to Ms. Merlene Moore for clerical assistance.
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