Lack of involution of hyperplastic parathyroid glands in dogs: adaptation via a decrease in the calcium stimulation...

Area of Science:

• Endocrinology
• Veterinary Medicine
• Nutritional Science

Background:

• Parathyroid hormone (PTH) plays a crucial role in calcium and phosphate homeostasis.
• Dietary deficiencies in calcium and vitamin D are known to impact parathyroid gland function.
• Understanding the long-term effects of such deficiencies and the recovery process is vital for animal health.

Purpose of the Study:

• To analyze the impact of a prolonged low-calcium, high-sodium, vitamin D-deficient diet on parathyroid function in dogs.
• To evaluate the recovery of parathyroid function following dietary correction and vitamin D supplementation.
• To assess changes in the molecular forms of immunoreactive parathyroid hormone (iPTH) during deficiency and recovery.

Main Methods:

• Four dogs were subjected to a 2-year diet low in calcium and vitamin D.
• Parathyroid function was assessed via intravenous infusions of calcium chloride (CaCl2) and disodium EDTA (Na2 EDTA).
• Intact (I) and carboxyl-terminal (C) iPTH levels were measured, and the C-iPTH/I-iPTH ratio was calculated to analyze iPTH molecular forms.

Main Results:

• The deficiency diet significantly lowered ionized calcium and 25-hydroxyvitamin D (25-OHD) levels.
• Basal and stimulated levels of both I-iPTH and C-iPTH increased approximately eightfold and fivefold, respectively.
• A decreased C-iPTH/I-iPTH ratio was observed, indicating a shift in circulating iPTH molecular forms.

Conclusions:

• Prolonged calcium and vitamin D deficiency severely impacts canine parathyroid function, leading to elevated iPTH levels.
• Dietary correction and vitamin D supplementation can reverse these effects, restoring parathyroid function.
• The study highlights the dynamic changes in iPTH molecular forms in response to nutritional status and treatment.