The lipolytic effect of cyclic 3′, 5′-adenosine monophosphate (cAMP) is inhibited by the beta-adrenergic blocker propranolol. This is demonstrated on both isolated fat cells and intact epididymal fat pad preparations. A cell-free extract of either rat or human adipose tissue contains a lipase system which can be activated by cAMP. This activation is also prevented by propranolol as well as the alpha-adrenergic blocker, phentolamine, in a dose-related fashion. Because of this nonspecific action, pharmacologic differentiation of alpha- or beta-adrenergic receptor sites should be based upon direct measurements of cyclic nucleotide, adenyl cyclase or phosphodiesterase, and not target enzyme activity.

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