Norepinephrine‐Induced Shift in Levels of Adenosine 3′:5′‐monophosphate and ATP Parallel to Increased Respiratory Rate and Lipolysis in Isolated Hamster Brown‐Fat Cells

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Abstract
1 Isolated brown fat cells from hamster respond to added catecholamines with a temporary increase in respiratory rate and an extended lipolysis. 2 From experiments with catecholamines and α and β-blockers, the receptors of these cells are classified as β according to classical definition. 3 Norepinephrine induces a rapid increase in adenosine 3′:5′-monophosphate levels which parallels in time the stimulated respiration. Maximal adenosine 3′:5′-monophosphate levels are reached within 1–3 min and are followed by a continuous decline. 4 Parallel to the catecholamine-induced respiration and lipolysis there is a pronounced drop in ATP levels. This energy depletion could be reversed by addition within 5 min after norepinephrine of the β-blocker propranolol. 5 The nucleotide pattern in isolated hamster brown fat cells after norepinephrine addition was mimicked in experiments with isolated hamster brown fat mitochondria. From these experiments it is concluded that a high ratio of AMP and ADP over ATP decreases the respiratory rate when endogenous free fatty acids are oxidized.