What are the main hormones involved in calcium homeostasis ?
- Parathyroid hormone (PTH)
- Vitamin D
- Calcitonin
What are the role of PTH and target organs ?
PTH ↗︎ eC [Ca2+]
Target organs : bones and kidney
What are the role of vitamin D and target organs ?
1,25(OH)2D or calcitriol (active form of Vitamin D) ↗︎ eC [Ca2+] (more delayed effect than PTH)
Target organs :
* bones
* kidney
* intestine
* ⊖ PTH
From which organ Calcitonin is secreted ?
What are the role of Calcitonin and target organs ?
Calcitonin, from C-cells of thyroid gland, ↘︎ eC [Ca2+]
Main target organ : bone
What are the main sources of Ca2+ excretion ?
- Renal (++)
- Feces
- Sweat (+)
- Milk (++)
Which factor influences [Ca2+] ?
pH
* Acidemia = ↗︎ Ca2+
* Alkalosis = ↘︎ Ca2+
Which factor influences [total Ca] ?
Albumin
Hypo-albuminemia = ↘︎ tCa → pseudo-hypocalcemia
Hyper-proteinemia = ↗︎ tCa
What are the clinical signs of hypercalcemia ?
Horses are very tolerant to hypercalcemia. Clinical signs are often due to the primary disease.
Severe cases (poor prognosis) → neuro. signs, muscle weakness, constipation, polyuria
DDX of hypercalcemia
1- Renal failure (acute and chronic) : ↗︎ Ca and ↘︎ P
2- Hypercalcemia of malignancy : ↗︎ PTHrP → pseudohyperparathyroidism or paraneoplastic syndrome
3- Vitamin D toxicosis (plants) : ↗︎ Ca and ↘︎ P
4- Primary hyperparathyroidism : parathyroid adenoma
5- Hypercalcemia in foals : with asphyxia
What to do with hypercalcemia ?
1- Re-check tCa and Ca2+
2- Evaluate renal function
3- Measure [P]
4- Measure [PTH]
5- Measure vitamin D metabolites
What to do with hypocalcemia ?
1- Re-check tCa and Ca2+
2- Measure [albumin]
3- Evaluate clinical signs
4- Measure [PTH]
TT of hypercalcemia ?
1- Decrease Calcium intake : diet (grass hay rather than alfalfa)
2- Increase renal excretion : fluidotherapy +/- furosemide
Clinical signs of hypocalcemia ?
Depression, tachycardia, tachypnea, profuse sweating, muscle fasciculation, synchronous diaphragmatic flutter
DDX of synchronous diaphragmatic flutter
- Hypocalcemia
- Hypochloremic metabolic alkalosis
- Hypokalemia
DDx of hypocalcemia ?
- Colic : strangulating intestinal lesion
- Acute diarrhea : hypoCa, hypoMg, hyperP, acidosis
- Endotoxemia
- Lactation tetany : rare, during first week of lactation
- Nutritional secondary hyperparathydoidism : due to low Ca or high P in the diet → osteodystrophia fibrosa
- Exhaustion syndrome in exercising horses : loss of Ca2+, K+ and Cl- in sweat → synchronous diaphragmatic flutter
- Cantharidin toxicosis
- Primary hypoparathydoidism (rare) : low Ca with low PTH
What is the most important cause of hypocalcemia in foals ?
Sepsis
TT of hypocalcemia ?
Fluid therapy : calcium borogluconate
Many hypoCa horses are also hypoMg → both supplementation
What are the recommendation for Ca/P ratio diet ?
Ca/P ≧ 2/1
