| Abstrakt: |
The effects of epinephrine (as low as 0.1 μM) on guanosine 3′:5′-cyclic monophosphate (cGMP) and adenosine 3′:5′-cyclic monophosphate (cAMP) in isolated fat cells were examined. Epinephrine increased both cGMP and cAMP levels, with the elevation of cAMP preceding the rise of cGMP. Maximal elevation was obtained with 1 μM epinephrine for each nucleotide. The increase in content of cGMP and cAMP due to epinephrine was completely blocked by a β-adrenergic antagonist (5 μM propranolol). Phentolamine (10-100 μM), an α-adrenergic antagonist, enhanced the response to epinephrine resulting in elevation of cAMP levels, whereas a high concentration (100 μM) of phentolamine suppressed the elevation of cGMP. The ability of epinephrine to increase cGMP and cAMP levels was markedly diminished by “feedback regulator” partially purified from the incubation mixtures of isolated fat cells exposed to epinephrine [Ho, R.J. & Sutherland, E. W. (1971) J. Biol. Chem.246, 6822-6827], whereas an increase in cGMP, but not cAMP, levels was observed in isolated fat cells incubated with “feedback regulator” alone (without epinephrine). These observations suggest the possibility that the epinephrine-induced elevation of cGMP levels in isolated fat cells might be mediated by an increase in formation of intracellular “feedback regulator” due to an elevation of cAMP by epinephrine. |
