Clearance of iodoantipyrine I 131 (IAP) from the forearm of normal and atopic persons was determined before and after the intracutaneous injection of mecholyl. In both groups, and in normal and delayed blanch reactions, a similar increase in clearance was found following the mecholyl injections. While shifts in the distribution of flow cannot be excluded, these findings indicate that an overall increase in cutaneous blood flow takes place within delayed blanch reactions and suggest that vessels are dilated within these areas. The contrast between augmented blood flow in mecholyl blanch and greatly decreased blood flow in epinephrine blanch is a dramatic example of unreliability of skin color as an index of local blood flow.
Bystryn JC, Freedman RI, Hyman C. Clearance of Iodoantipyrene From Methacholine Blanched Skin in Atopics. Arch Dermatol. 1969;100(2):165-168. doi:10.1001/archderm.1969.01610260041006