Differential activation of β1‐, β2‐ and β3‐adrenoceptors by catecholamines in white and brown adipocytes

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Abstract
Summary—This review summarizes the experiments performed by various groups to determine how the activation of the different β‐adrenoceptors (β‐ARs) is ordinated when they are present in the same fat cell and involved in the same biological event. When expressed after the transfection of their genes in Chinese hamster ovary cell (CHO cells), β1‐ and β2‐ARs present a higher affinity for catecholamines than β3‐ARs.In vitro, the lipolytic effect induced by low concentrations of catecholamines in dog and rat white fat cells is due to the selective activation of β1‐ and/or β2‐ARs. Higher concentrations only are able to activate β3‐ARs. Similar results have been obtained in rat brown adipocytes. On the other hand, the lipolytic effect of catecholamines in human and primate adipocytes does not involve a β3‐AR component whatever the concentration used.In vivoexperiments in the dog have also shown that lipomobilization induced by low doses of isoprenaline only involved β1‐ and β2‐AR activation, this effect being blocked by β1‐/ β2‐antagonist pretreatment. However, in the same blockade conditions, perfusion of a 10‐fold higher dose of isoprenaline revealed a β3‐AR contribution in the lipomobilizing effect. These data showed that brown and white adipocyte β3‐ARs possess a lower affinity for catecholamines than β1‐ and β2‐ARs and are only recruited by high concentrations of the amines. Thus, even if the β3‐AR plays an indisputable role in the white and brown adipose tissue of some species, its physiological status and its expression are still subject to debate in human white fat cells.