Objectives: To determine the effects of treating canine hyperadrenocorticism (HAC) on parathyroid hormone (PTH), calcium and phosphate concentrations in dogs.

Methods: Serum calcium, phosphate and PTH concentrations were analysed in 22 dogs with HAC before treatment with trilostane and at a median of 210 days after commencing treatment. Pretreatment data were compared with data from an age- and weight-matched group of hospitalised patients, and post-treatment data were compared with pretreatment data.

Results: PTH and phosphate concentrations were significantly higher in dogs with HAC compared with control dogs. PTH concentrations reduced significantly with treatment, such that there was no longer difference between the HAC and control groups. Phosphate concentrations also reduced significantly with treatment but there was still a significant difference between those in dogs with HAC and control dogs. Despite no significant difference between calcium concentrations in the pretreatment HAC and control groups, calcium concentrations increased significantly with treatment.

Clinical Significance: These results show that adrenal secondary hyperparathyroidism resolves with treatment and suggest that increased calcium and phosphate levels have a role in its pathogenesis.