Pathophysiology of grass tetany and other hypomagnesemias. Implications for clinical management.
Level 5 - mechanism / opinion, no new human data
Narrative review and mechanistic physiological modeling of animal data
PubMed 11022344 · doi:10.1016/s0749-0720(15)30109-2
What was done
This narrative review synthesizes in vitro and in vivo physiological studies investigating magnesium homeostasis, epithelial transport across the forestomach wall in ruminants, and the neurological mechanisms underlying grass tetany. It evaluates proposed transport models involving potential difference (PD)-dependent and PD-independent apical uptake, basolateral sodium/magnesium exchange, and the modifying effects of dietary potassium, sodium deficiency, ammonium, and short-chain fatty acids.
What was found
The abstract describes mechanistic relationships rather than clinical trial endpoints. In the proposed model, ruminal magnesium uptake involves both PD-dependent and PD-independent mechanisms alongside basolateral Na/Mg exchange. Elevated ruminal potassium depolarizes the apical membrane potential, reducing PD-dependent magnesium uptake when ruminal magnesium concentrations remain below 2 to 3 mM. When ruminal magnesium exceeds 2 mM, the PD-independent pathway predominates, allowing absorption to occur despite high potassium levels. High ammonium concentrations transiently reduce ruminal magnesium absorption. Hypomagnesemic excitation and muscle spasms correlate directly with decreased magnesium concentrations in the cerebrospinal fluid.
Why it matters
This framework explains the cellular mechanism by which lush pastures high in potassium trigger grass tetany and clarifies why high-dose oral magnesium supplementation provides effective clinical prophylaxis despite elevated dietary potassium.
Limits
The paper is a narrative review without systematic search criteria, meta-analytic pooling, or reported sample sizes. Many underlying transport models rely on in vitro tissue preparations, and specific quantitative thresholds in varied production herds were not evaluated in randomized field trials within the abstract.
Cited by
- supports In cattle, magnesium deficiency from low-magnesium forage causes 'grass staggers' (hypomagnesemic tetany), which manifests as fatal convulsions if untreated.