Rapidity of plasma 1,25-dihydroxyvitamin D responses to hypo- and hypercalcemia in steers.
Experiments were designed to study the rapidity of changes in plasma 1,25-dihydroxyvitamin D [1,25-(OH)2D] levels in response to hypercalcemia and hypocalcemia induced by 10-h infusions of CaCl2 or EGTA in steers. In response to CaCl2 infusions, 1,25-(OH)2D was decreased within 4 h (P less than 0.05) and remained lower (P less than 0.05) than preinfusion concentrations for up to 14 h after termination of the infusions. PTH and inorganic phosphate (Pin) transiently decreased in response to the CaCl2 infusions, whereas total magnesium (Mg) continuously fell for up to 24 h after the start of the infusions. In response to infusions with EGTA, on the other hand, 1,25-(OH)2D continuously increased and was raised significantly (P less than 0.05) between 12 and 24 h after the start of the infusions. PTH increased within 2 h (P less than 0.05) and remained elevated (P less than 0.05) for up to 2 h after the end of the EGTA infusions, whereas Pin and Mg were not significantly changed. During and after 10-h control infusions of sodium chloride, the levels of 1,25-(OH)2D, PTH, Ca, Ca++, Pin, and Mg remained unaltered. In conclusion, plasma levels of 1,25-(OH)2D were lowered in response to hypercalcemia within 4 h and increased in response to hypocalcemia within 12 h. After termination of the infusions with CaCl2 or EGTA, levels of 1,25-(OH)2D remained decreased or elevated for at least 14 h, even though Ca, Ca++, and PTH levels were normalized. The slow changes in 1,25-(OH)2D contrast with the rapid responses of PTH to hyper- and hypocalcemia.
D000818:Animals; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood; D002122:Calcium Chloride / Q000494:pharmacology; D002369:Castration; D002417:Cattle; D004533:Egtazic Acid / Q000494:pharmacology; D006934:Hypercalcemia / Q000097:blood*; D007700:Kinetics; D008274:Magnesium / Q000097:blood; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood; D012965:Sodium Chloride / Q000494:pharmacology
D010281:Parathyroid Hormone; D010710:Phosphates; D012965:Sodium Chloride; D004533:Egtazic Acid; D002117:Calcitriol; D008274:Magnesium; D002122:Calcium Chloride; D002118:Calcium