Beta-3 adrenoceptor-mediated increase in cutaneous blood flow in the dog

Beta-3 adrenergic agonist administration decreases arterial blood pressure in the dog as previously shown. The putative presence of beta-3 adrenoceptors in peripheral microvascular muscle was studied in dogs through measurement of cutaneous blood flow and skin temperature changes. Experiments were carried out in normal and sinoaortic denervated dogs (i.e., animals deprived of baroreceptor pathways). In normal dogs, the infusion of 0.4 nmol/kg/min of 4-[-[(2-hydroxy-(3-chlorophenyl)ethyl)-amino]propyl] phenoxyacetate (BRL 37344) or (R,R-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3- benzodioxole-2,2-dicarboxylate (CL 316243) (two selective beta-3 adrenoceptor agonists), or 8 nmol/kg/min of 4-[3-t-butylamino-2-hydroxypropoxy]benzimidazol-2-one (CGP 12177) (a beta-1/beta-2 adrenergic antagonist also reported to act as an agonist for the beta-3 adrenoceptor) induced an increase in heart rate and cutaneous blood flow (evaluated in the internal part of the ear) and a decrease in blood pressure. The skin and the buccal mucous membrane became purplish. The infusion of (-)-isoproterenol (0.4 nmol/g/min), a dose known to stimulate preferentially beta-1/beta-2 adrenoceptors, or sodium nitroprusside (12 micrograms/kg/min) increased heart rate and decreased blood pressure, but reduced cutaneous blood flow. In sinoaortic denervated dogs, similar effects on cutaneous blood flow and blood pressure were observed. However, in these animals, heart rate remained unchanged whatever the infused drug. BRL 37344 (but not isoproterenol) increased cutaneous temperature in normal dogs. This study suggests that beta-3 adrenoceptors exist in canine cutaneous vascular smooth muscles and that their stimulation induces vasodilatation.