Pathogenesis of hypocalcemia in magnesium depletion. Normal end-organ responsiveness to parathyroid hormone.
Hypocalcemia in the hypomagnesemic state in man is usually attributed to refractoriness of end-organs to the calcemic action of parathyroid hormone. We studied the responsiveness of end-organs to bovine parathyroid extract (PTE) in magnesium-depleted and control dogs by the following three methods after thyroparathyroidectomy: (a) assessment of the calcemic response to a set dose of PTE (0.3 U/kg per hr); (b) assessment of PTE dose required to attain normocalcemia; (c) evaluation of regression lines of plasma calcium concentration on PTE dose. The calcemic response of magnesium-depleted thyroparathyroidectomized puppies to a set dose of PTE was similar to that of control puppies. There was no significant difference in the dose of PTE required to attain normocalcemia nor in the dose-response relations between the plasma calcium concentration and the PTE dose. In a group of magnesium-depleted puppies with intact thyroid and parathyroid glands, the dose of PTE required to attain normocalcemia was similar to that required in thyroparathyroidectomized animals, indicating calcitonin was not a factor contributing to hypocalcemia. We conclude that hypocalcemia in magnesium-depleted puppies is not due to refractoriness of end-organs to the calcium-mobilizing action of parathyroid hormone. Defective synthesis or diminished secretion of parathyroid hormone is suggested as an explanation.
D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D001798:Blood Proteins / Q000032:analysis; D002118:Calcium / Q000097:blood; D004032:Diet; D004285:Dogs; D005215:Fasting; D005260:Female; D006996:Hypocalcemia / Q000209:etiology*; D007275:Injections, Intravenous; D008274:Magnesium / Q000097:blood; D008275:Magnesium Deficiency / Q000150:complications*; D010280:Parathyroid Glands / Q000503:physiopathology; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D010710:Phosphates / Q000097:blood; D013961:Thyroid Gland / Q000503:physiopathology; D013965:Thyroidectomy; D013974:Thyroxine / Q000008:administration & dosage; D013997:Time Factors
D001798:Blood Proteins; D010281:Parathyroid Hormone; D010710:Phosphates; D000469:Alkaline Phosphatase; D008274:Magnesium; D013974:Thyroxine; D002118:Calcium