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To determine effects of exercise on blood ionized calcium (Ca2+) and plasma parathyroid hormone (PTH) concentrations in horses and to compare the effects of exercise-induced and EDTA-induced hypocalcemia on PTH secretion.


17 horses entered in a show jumping competition and 5 horses given EDTA.


Blood Ca2+ and plasma PTH concentrations were measured before and after exercise in the 17 horses entered in the jumping competition. In the other 5 horses, concentrations were measured during infusion of EDTA IV.


Exercise resulted in a significant decrease in blood Ca2+ concentration and a significant increase in plasma PTH concentration, and blood Ca2+ concentration was correlated with plasma PTH concentration. Administration of EDTA resulted in hypocalcemia and an increase in PTH concentration. For the same decrease in Ca2+ concentration, magnitude of the exercise-induced increase in PTH concentration was similar to magnitude of the EDTA-induced increase.

Conclusions and Clinical Relevance

Results suggest that the increase in plasma PTH concentration in horses after exercise is secondary to hypocalcemia and that the increase in PTH concentration seems to be commensurate with the decrease in Ca2+ concentration. (Am J Vet Res 1998;59:1605-1607)

Free access
in American Journal of Veterinary Research


The ability of ectopic parathyroid tissue to support calcium homeostasis was evaluated by measuring serum concentrations of calcium, phosphorus, albumin, magnesium, and parathyroid hormone before and for 12 weeks after bilateral thyroparathyroidectomy in 14 cats. During the immediate postoperative period, significant decrease was observed in serum calcium, magnesium, and parathyroid hormone (pth) concentrations. Serum pth concentration remained subnormal and did not significantly increase during the 12-week observation period. Despite persistent hypoparathyroidism, serum calcium and magnesium concentrations gradually increased. Ectopic parathyroid tissue is not capable of maintaining normal serum calcium concentration immediately after thyroparathyroidectomy. Serum calcium concentration gradually normalizes after thyroparathyroidectomy, apparently by means of a pth-independent mechanism.

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in American Journal of Veterinary Research

. Compliance was calculated by use of the following equation: C = (Vth − V0)/(Pth − P0), where C is compliance, Vth is threshold volume, Pth is threshold pressure, and V0 and P0 are the intravesicular volume and pressure, respectively, at the start of

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in American Journal of Veterinary Research