Dopamine effects on the microcirculation and veins of the skin after local application and their changes by antagonistic drugs.

Dopamine causes reflex erythema, central blanching, and piloerection depending on the dose and the type of application wheal reaction. Intracutaneous application shows from 1.5 gamma/0.1 ml wheal formation, erythema, piloerection, and blanching combined with increased heat radiation from the skin surface (AGA thermovision). Epicutaneous application from 500 ml (occlusive patch test) following horny layer stripping, causes marked blanching with weak piloerection. Iontophoretic application of dopamine 1/1,000 (60 s, 0.5 mA) causes only blanching and weak surrounding erythema; application of dopamine 1/100 additionally causes piloerection. This application shows no changing of infrared radiation. Iontophoretic application of dopamine 1/100 or 50 gamma/0.1 ml i.c. in a blanched area after locally applied corticosteroids (McKenzie test) shows diminution of infrared radiation proved by AGA thermovision thermography. Antihistaminics, applied externally, decrease reddening, wheal development as well as blanching by dopamine. Guanethedine (1% in eucerin) increases the blanching phenomenon (false transmitter effect of dopamine). Phentolamine 1% in W/O emulsion is without effect on dopamine reaction. Caffeine ointment (4%) reduces erythema and accentuates the degree of blanching. Oral haloperidol has no influence on the dopamine skin reaction, but increases the blanching in areas of antihistamine treatment. Skin veins and varices show marked vasoconstriction within 10 min after iontophoretic (1 : 100, 3.5 mA, 60 s) or i.c. application (50 gamma/0.2 ml).