A conceptual approach that relates
vascular headaches, bowel and bladder dysfunction to abnormalities of the "
ammonia potassium axis" is presented.
Hypokalemia alters smooth muscle function of both the bowel and bladder and results in the elaboration of an alkaline urine. The occurrence of an alkaline urine, along with bladder dysfunction and urinary stasis, predisposes to recurrent
urinary tract infections.
Hypokalemia and/or
alkalosis increases the renal return of
ammonia, exposes the brain to chronically higher concentration of
ammonia and facilitates its passage into the central nervous system. Increased levels of blood
ammonia predispose to
hyperventilation which results in a superimposed
respiratory alkalosis on a pre-existing
hypokalemia and/or
alkalosis therefore causing intense cerebral vasoconstriction. Varying degrees of
cerebral ischemia and
hypoxia occur and give rise to higher brain concentrations of
ammonia. Vasodilatation occurs during the
headache phase and may be a consequence of the sudden increase of brain
ammonia and/or due to the release of other vasoactive mediators. As a consequence of increased blood
ammonia, a reduction of
protein intake may result in the alterations of
amino acid precursors for brain uptake and therefore further interferes with the modulation of cerebral blood flow and brain function.