THE RELATIONSHIP BETWEEN VITAMIN D AND PARATHYROID HORMONE

Early changes in enzyme activity during the development of and recovery from vitamin D deficiency in the rat

1. Rats were given a rachitogenic diet with or without vitamin D for 1, 2, 3 or 4 weeks, and vitamin D was administered to a group of rats which had been deprived of vitamin D for 3 weeks. 2. Changes in enzyme activities of some tissues were followed histochemically. In general, changes in parathyroid preceded those in gut and kidney. Leucine aminopeptidase activity rose in the parathyroid, kidney and jejunum of the vitamin D-deficient rat as did the ribonucleic acid content of the parathyroid and the dehydrogenase activity of the gut. In contrast, the phosphatase activity of the gut and kidney fell in the vitamin D-deficient rat. All these changes were reversed during the 1-week recovery period. 3. A slower response of bones to both vitamin D deprivation and vitamin D dosage after deprivation was indicated by the changes in the percentages of ash in the bones and the changes in number and distribution of osteoclasts.

On the relationship between vitamin D action and actinomycin-sensitive processes

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Actinomycin D and the Response to Parathyroid Hormone

Actinomycin D inhibits the effect of parathyroid hormone upon bone, as measured by calcium mobilization, without altering its effects upon the renal excretion of phosphate and calcium.