Spontaneous histamine release after exposure to hyperosmolar solutions

Since basophils from certain allergic individuals release histamine spontaneously in aqueous or deuteriumoxide-containing buffers, we examined spontaneous release after a brief exposure to hyperosmolar buffers. With leukocytes from 71 normal and allergic volunteers, it was found that 15-minute suspension in 770 mosm/kg Ca⁺⁺-free buffers caused the cells to release 3% to 83% of cellular histamine (mean 29 ± 3) when the cells were resuspended in isosmolar buffers containing Ca⁺⁺. The cells from individuals with a history of food allergy were significantly more easily activated when the cells were compared to cells of normal volunteers (p < 0.005), but cells from other allergic volunteers were more readily activated as well. Activation was maximal at 770 Mosm/kg and occurred in the absence of Ca⁺⁺, whereas subsequent histamine release was partially Ca⁺⁺ dependent. Activation could be observed as early as 30 seconds and was maximal at 15 minutes; histamine release from activated cells was almost as rapid. We conclude that the basophils from certain allergic individuals demonstrate unusual "releasability" and that this responsiveness to osmotic activation could play a role in reactions to hyperosmolar radiocontrast media.