Phosphorus and protein restriction and parathyroid function in chronic renal failure

Area of Science:

• Nephrology
• Endocrinology
• Nutritional Science

Background:

• Chronic renal failure (CRF) often leads to phosphorus retention and secondary hyperparathyroidism (HPT II).
• Low-phosphorus, low-protein diets (LPD) are used to manage HPT II in CRF patients.
• The specific impact of LPD on the relationship between calcium and parathyroid hormone (PTH) in advanced CRF needs further elucidation.

Purpose of the Study:

• To assess the effects of a specific LPD on the relationship between ionized calcium (iCa) and PTH concentrations in patients with advanced CRF and HPT II.
• To determine if LPD influences PTH secretion independently of calcitriol levels.

Main Methods:

• Seven patients with advanced CRF and HPT II were placed on a LPD for three months.
• The diet provided 5-7 mg/kg phosphorus, 0.4 g/kg protein, 300 mg calcium, supplemented with amino acids, ketoacids, CaCO3, and vitamin D2.
• Hyper- and hypocalcemia were induced using CaCl2 and Na2-EDTA infusions to analyze the PTH-calcium curve.

Main Results:

• Serum phosphorus and basal PTH levels significantly decreased after three months of LPD.
• The sigmoidal PTH-calcium curve shifted downward, indicating reduced maximal and minimal PTH levels.
• No significant changes were observed in basal iCa, glomerular filtration rate (GFR), or the sensitivity of parathyroid cells to iCa.

Conclusions:

• LPD directly inhibits PTH secretion in patients with advanced CRF and mild HPT II.
• This inhibitory effect on PTH occurs over a wide range of iCa concentrations.
• The observed reduction in PTH secretion by LPD is independent of changes in plasma calcitriol levels.