The effect of experimental hyperthyroidism, 150µg/kg/day/42 days, on calcium homeostasis was studied in 14 mongrel cats aging from one to three-year-old. Total thyroxine (T4), free thyroxine (FT4), parathyroid hormone (PTH), total and ionized calcium, phosphorus, bone mineral density were measured. Serum concentrations of PTH of increased from the initial moment (MO), with significant differences to when measured after 14(M1), 28(M2), and 42(M3) days. However, significant differences on serum concentrations were not observed among the values of M1, M2, and M3. The ionized calcium significantly decreased from M0 to M1 and from M1 to M3. Thyroid hormones showed positive correlation with PTH and negative with ionized calcium. Bone mineral density showed negative correlation with PTH from M2 to M3 and with phosphorus on M2, with no correlation with the other variables. Negative correlation of PTH with ionized calcium was observed on M1, M2, and M3. In conclusion, hyperthyroidism in young adult cats is associated to secondary hyperparathyroidism due to increase of PTH and decrease of ionized calcium. The combined effects of thyroid hormones and PTH contributed to the reduction of bone mineral density.
cat; hyperthyroidism; parathyroid hormone; calcium; phosphorus; bone density