Re‐sensitization of desensitized histamine H1 receptors in the human skin takes more than 18 hours

Abstract

Background: It is known since the time of testing histamine on pieces of guinea pig's jejunum that histamine receptors can develop insensitivity. The aim was to find evidence for desensitization of histamine H1 receptors in the human skin in vivo and, if found, to study the time for such receptors to regain normal sensitivity. Materials and Methods: A skin prick test with histamine (10 mg mL-1) was set in areas where a large histamine wheal was evoked 2, 6, 18, 24 or 72 hours earlier. A skin prick test with histamine (10 mg mL-1) was also set in an area where an allergen wheal was evoked 2 or 6 hours earlier. Heights, diameters and areas were measured on photographs of side views of plaster casts of the evoked skin elevations. Results: Histamine wheals, called test wheals, in areas where large histamine wheals were evoked 2, 6 or 18 hours earlier, were smaller than histamine wheals, called initial wheals, in earlier non-stimulated areas. Test wheals from the 18 hours experiment were smaller than test wheals from the 72 hours experiment. Test wheals evoked in areas where allergen wheals were evoked 2 or 6 hours earlier were smaller than corresponding initial wheals. Conclusion: Histamine-evoked wheals and IgE-mediated allergic wheals reduce the sensitivity of histamine H1 receptors in the human skin. It takes between 18 and 72 hours to restore the sensitivity. Similarities between the development of histamine wheals in the human skin and histaminergic migraine with aura are discussed.

Reduced ability to produce reflex‐evoked neurogenic inflammation, a sign of decreased defense against COVID‐19 infection?

“…The positive casts of the old subjects were photographed from the side and compared to similar photographs of casts of six healthy men (mean age 50) presented in a recent study by the author. 8 The technique to take the casts was the same as in the present study. It was thus possible to compare the results of the old men with three different series of results of the six younger men.…”