Effects of phentolamine on dibutyryl cyclic AMP and norepinephrine in rats anesthetized with amobarbital.

In vitro evidence demonstrated that norepinephrine (NE) increased endogenous levels of cyclic AMP in brain tissue. In vivo findings showed that in rats anesthetized with amobarbital, NE certrally administered prolonged narcosis whereas exogenous dibutyryl cyclic AMP shortened it. Phentolamine, an alpha adrenergic receptor inhibitor, administered centrally prolonged narcosis but did block all symptomatology accompanying its administration. Phentolamine added to dibutyryl cyclic AMP dose-relatedly antagonized the shortening of the duration of narcosis. Such ovservations suggest that whereas the inhibitory action of phentolamine affects NE at the alpha adrenergic receptor site, it antagonizes cyclic AMP at other sites as well.