Normocalcemia without hyperparathyroidism in vitamin D-deficient rats

Area of Science:

• Nutritional Biochemistry
• Endocrinology
• Animal Models

Background:

• Establishing vitamin D deficiency in rats without confounding hormonal or mineral changes is challenging.
• Accurate investigation of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] roles requires a reliable deficiency model.
• Existing dietary methods fail to isolate vitamin D's effects from parathyroid hormone (PTH), calcium (Ca), and phosphate fluctuations.

Purpose of the Study:

• To develop and validate a novel dietary regimen for inducing vitamin D deficiency in rats.
• To ensure the diet avoids altering plasma calcium, phosphate, and parathyroid hormone levels.
• To facilitate precise research into the physiological functions of vitamin D metabolites in target tissues.

Main Methods:

• Rats were fed one of four diets for six weeks: control (+D3), vitamin D deficient (-D) with standard Ca/P, -D with high Ca/P, or -D with high Ca/P and lactose.
• Plasma levels of calcium, phosphate, N-terminal PTH, 25-hydroxyvitamin D3 (25-OHD3), and 1,25-(OH)2D3 were measured.
• Dietary groups included: A (+D3), B (-D, standard Ca/P), C (-D, high Ca/P), and D (-D, high Ca/P + lactose).

Main Results:

• Rats on the diet with high Ca, high P, and lactose (Group D) maintained normal plasma Ca and phosphate levels.
• Rats on high Ca/P diets without lactose (Group C) or standard diets (Group B) became hypocalcemic and showed elevated PTH.
• All vitamin D deficient groups exhibited significantly reduced plasma 25-OHD3 and 1,25-(OH)2D3 levels.

Conclusions:

• A novel diet combining high calcium, controlled Ca/P ratio, and lactose successfully induces vitamin D deficiency in rats.
• This diet maintains normocalcemia and normophosphatemia, unlike previous methods, and does not elevate PTH.
• This validated model provides a crucial tool for studying vitamin D's specific physiological roles.