Low-calcium/high phosphorus rickets in rats. I. Mast cell changes

Area of Science:

• Bone biology
• Cellular biology
• Nutritional science

Background:

• Nutritional deficiencies, specifically low calcium and high phosphorus, can significantly impact bone health.
• Vitamin D plays a crucial role in calcium and phosphorus metabolism and bone integrity.
• Mast cells are immune cells involved in inflammatory and tissue repair processes.

Purpose of the Study:

• To investigate the effect of a low calcium/high phosphorus diet on bone changes and mast cell accumulation in weanling rats.
• To examine the secretory activity of mast cells in response to induced hypocalcemia and rachitic bone changes.
• To determine the potential role of mast cells in bone remodeling under specific dietary conditions.

Main Methods:

• Weanling rats were fed a diet with low calcium (0.003%) and high phosphorus (0.64%), with and without vitamin D, for up to 5 weeks.
• Blood calcium levels, bone morphology (rachitic changes), and bone resorption were assessed.
• Light and electron microscopy were used to study mast cell morphology, distribution, and secretory activity in long bone metaphyses and other tissues.

Main Results:

• The low calcium/high phosphorus diet induced hypocalcemia, rachitic bone changes, and increased bone resorption.
• A significant accumulation of mast cells was observed in the metaphyses of long bones, preceding other observed changes.
• Mast cells exhibited increased secretory activity, indicated by granule alterations and content release, especially in rats with the lowest serum calcium.
• Mast cell increase was specific to metaphyses and not observed in epiphyses or other organs.

Conclusions:

• Diet-induced hypocalcemia and bone resorption in rats are associated with a localized increase in mast cells in long bone metaphyses.
• Mast cells in affected bone regions display enhanced secretory activity, suggesting a role in response to metabolic bone disease.
• The accumulation and activation of mast cells may be linked to maintaining connective tissue integrity during periods of rapid bone remodeling or damage.