Participation of a β-Adrenergic System in Dopamine Stimulation of Respiration in Isolated Rat Brown Adipocytes

Abstract

The characteristics of dopamine- and norepinephrine-stimulation of respiration in isolated rat brown adipocytes were compared. Although both dopamine and norepinephrine rapidly stimulated the respiration and lipolysis of isolated cells, much higher concentrations of dopamine compared to norepinephrine were required to cause the same extent of response. Antagonists of the dopamine receptor (haloperidol) and of the β-adrenoreceptor (propranolol) suppressed respiration that was stimulated by either dopamine (50 μM) or norepinephrine (0.2 μM). Unexpectedly, dopamine-stimulated respiration was completely inhibited by the β-adrenergic blocker at a concentration far lower than that required to inhibit norepinephrine-stimulated respiration. Both catecholamines added at concentrations of a large excess to stimulate respiration overcame the inhibitory action of propranolol but not of haloperidol. An agonist of the dopamine receptor, apomorphine (50 μM), failed to stimulate the respiration of brown adipocytes. These results indicate that dopamine at a high concentration stimulates the respiration of brown adipocytes primarily through interaction with the β-adrenoreceptor, but not with the dopamine receptor.