Histamine response and local cooling in the human skin: involvement of H-1- and H-2-receptors

Aims Histamine may contribute locally to cutaneous blood flow control under normal and pathologic conditions. The objective of this study was to obser ve the influence of skin temperature on histamine vasodilation, and the rol es of HI-and H-2-receptors using novel noninvasive methods. Methods Eleven healthy subjects received, double-blind, single doses of the H-1 receptor antagonist cetirizine (10mg), cetirizine (10mg) plus the H-2- receptor antagonist cimetidine (400 mg), or placebo on separate occasions. Histamine was dosed cumulatively by iontophoresis to the forearm skin at 34 degrees C and 14 degrees C. Laser-Doppler flux (LDF) was measured at the s ame sites using customised probeholder/ iontophoretic chambers with Peltier cooling elements. Finger mean arterial pressure (MAP) was measured and cut aneous vascular conductance calculated as LDF/MAP. Results Histamine vasodilation was reduced in cold skin. Cetirizine shifted the histamine dose-response at both temperatures: statistically significan tly at 14 degrees C only. Combined H-1- and H-2-receptor antagonism shifted the response significantly at both temperatures. Conclusions H-1- and H-2-receptors mediate histamine-induced skin vasodilat ion. The sensitivity of these receptors, particularly the H-1- receptor, is attenuated at low skin temperature. Whether the reduced effect in cold ski n represents specific receptor or postreceptor desensitization, or nonspeci fic attenuation of cutaneous vasodilation remains to be elucidated.