Activation of beta3-adrenoceptors by exogenous dopamine to lower glucose uptake into rat adipocytes.

The effect of dopamine hydrochloride on beta3-adrenoceptors was studied in isolated adipocytes of Wistar rats using uptake of [14C]-deoxy-D-glucose (2-DG) as the indicator. Dopamine induced a concentration-dependent decrease of 2-DG uptake into adipocytes in a manner which was not modified by haloperidol at concentrations sufficient to block dopaminergic receptors. Failure of blockade was also observed in samples receiving the pretreatment with a mixture of SCH23390 and domperidone, the dopaminergic antagonists. Absence of dopaminergic receptors in rat white adipocytes was further supported by the findings that dopaminergic agonists did not modify the glucose uptake and the negative response to receptor antibodies in immunoblotting analysis. Pindolol and propranolol reversed this inhibition of dopamine in a concentration-dependent manner. However, this action of dopamine was not affected by prazosin at concentrations sufficient to block alpha-adrenoceptors. Effect of dopamine was reduced in the presence of Rp-cyclic AMPS triethylamine, the membrane-permeable antagonist of cyclic AMP (cAMP), indicating the mediation of cAMP in this inhibition. Direct effect of exogenous dopamine on beta3-adrenoceptors was identified using the antibody for beta3-adrenoceptors that reversed the inhibition of dopamine. These results suggest that dopamine can activate beta3-adrenoceptors to lower glucose uptake into rat white adipocytes which lack dopaminergic receptors.