GFR was stable in most dogs with parathyroidectomy between 12 and 24 months, whereas most dogs without parathyroidectomy experienced progressive decrease in GFR.122 Increases in PTH were prevented when dietary intake of phosphorus was substantially reduced (100 mg/day from 1200 mg/day) even during advanced stages of CKD.123 This was a pivotal study in determining that phosphorus control systems were important in the genesis of renal secondary HPTH. Here, PTH is linked to chronic kidney disease.