Effect of labetalol and propranolol on human cutaneous vasoconstrictor response to adrenaline

Using half-life disappearance of intradermally injected radioiodine as a parameter for cutaneous blood flow, a study was made of the effects of labetalol and propranolol on the vasoconstrictor response to adrenaline at environmental temperatures of 22 degrees C and 32 degrees C in seven healthy volunteers. Iodine clearance was reduced at 22 degrees C, and at both temperatures by 16 pcg of adrenaline. Orally administered propranolol (20 mg) enhanced these effects at the lower temperature and that of adrenaline at both temperatures. This method unequivocally demonstrates the aggravation of adrenaline-induced cutaneous vasoconstriction caused by oral administration of propranolol and distinguishes it from that caused by labetalol.