Low blood pressure causing lightheadedness or fainting is a classic manifestation of mast cell disease with as many as 22-55% of patients having experienced it at least one. For comparison, the control group demonstrated a frequency of 5%. Some patients experience this symptom often while others only rarely experience it or never do.
A staggering amount of mast cell mediators can induce low blood pressure; indeed, this is the reason why low blood pressure is the hallmark sign of severe allergic reaction and anaphylaxis. Histamine can induce hypotension through the H1 receptor. Heparin makes histamine and tryptase less susceptible to degradation, allowing longer action.
Many mediators are vasodilating, widening the blood vessels. Vasoactive intestinal peptide (VIP) is a vasodilator. PGD2 is also a very potent in this capacity. PGE2 is not released in large amounts by mast cells, but has the same effect. Platelet activating factor decreases blood pressure in multiple ways: by decreasing the force of heart muscle contraction, by slowing heart rate and by widening blood vessels. IL-6 and nitric oxide are also vasodilating.
Some mediators lower blood pressure by their participation in the bradykinin pathway. Bradykinin is a potent stimulator of fluid loss from the blood to the tissues, causing low blood pressure and angioedema. Heparin can serve as an initiator for the production of bradykinin. Tryptase and chymase both participate in bradykinin formation.
Mast cell medications can be very effective in increasing blood pressure by decreasing fluid loss from the blood to the tissues. As PGD2 can be a strong vasodilator, COX inhibitors like NSAIDs that interfere with prostaglandin production can help to increase blood pressure. Aspirin, 81-325mg once or twice daily, is sometimes recommended for adults that are not sensitive to the medication. Early data on the use of omalizumab (Xolair) in SM patients indicates that it may prevent episodes of sudden onset low blood pressure.
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