Alterations in serum parathyroid hormone and electrolyte concentrations and urinary excretion of electrolytes in horses with induced endotoxemia.
Authors: Toribio Ramiro E, Kohn Catherine W, Hardy Joanne, Rosol Thomas J
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Endotoxaemia triggers profound electrolyte disturbances in horses through mechanisms that remain incompletely understood, yet carry significant clinical implications for managing septic cases. Toribio and colleagues administered lipopolysaccharide (LPS) to 12 mares and compared their responses to six saline-treated controls, measuring serum electrolytes, parathyroid hormone (PTH), insulin, and urinary electrolyte excretion patterns over a 1-hour infusion period. Within this timeframe, LPS-infused horses developed marked hypocalcaemia (ionised calcium fell from 6.5 to 6.0 mg/dL), hypomagnesaemia (total magnesium from 0.78 to 0.62 mM), hypokalaemia (potassium from 4.3 to 3.0 mEq/L), and hypophosphataemia (phosphate from 3.4 to 1.7 mg/dL), alongside a 76-fold increase in tumour necrosis factor-alpha—whilst PTH increased four-fold despite persistent hypocalcaemia in two animals, and urinary fractional excretion of calcium and magnesium dropped significantly. These findings suggest that endotoxin-mediated inflammation causes both renal conservation and peripheral sequestration of divalent cations, potentially explaining why supplementation alone may prove inadequate in septic horses; clinicians should interpret low serum electrolytes in septic cases as evidence of severe systemic inflammation rather than simple depletion, and recognise that PTH response is variable and cannot be relied upon to restore calcium homoeostasis.
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Practical Takeaways
- •Horses with sepsis/endotoxemia commonly develop hypocalcemia and hypomagnesemia; monitoring serum calcium and magnesium levels is important for managing septic cases
- •PTH elevation in response to hypocalcemia may be blunted in some horses with endotoxemia, suggesting impaired regulatory mechanisms during severe systemic inflammation
- •Electrolyte abnormalities (low Ca, Mg, K, Pi) are consistent findings in endotoxemic horses and should guide supplementation and supportive therapy strategies
Key Findings
- •LPS-induced endotoxemia caused significant decreases in ionized calcium (6.5 to 6.0 mg/dL), ionized magnesium (0.53 to 0.43 mM), total magnesium (0.78 to 0.62 mM), potassium (4.3 to 3.0 mEq/L), and phosphate (3.4 to 1.7 mg/dL)
- •Serum PTH increased significantly from 1.3 to 6.0 pM despite hypocalcemia, though 2 horses failed to mount a PTH response
- •Urinary fractional excretion of calcium, magnesium, and potassium decreased significantly (by 64%, 68%, and 53% respectively), while phosphate and sodium excretion increased
- •Endotoxin administration produced systemic inflammation evidenced by TNF-alpha increase from 6.6 to 507 pg/mL, heart rate increase from 40 to 70 bpm, and WBC decrease from 7570 to 1960 cells/µL