Imipramine Isoproterenol

In rats deprived of a 5-HT input, via lesions with 5,7-dihydroxytryptamine (5,7-DHT) or by p-chlorophenylalanine (PCPA), chronic administration of DMI failed to down-regulate p-adrenoceptors, although the usual desensitization of NE sensitive adenylate cyclase was still observed.62,63 when NE receptors were desensitized and reduced in number by the DMI treatment, PCPA reversed the decrease of p-receptors without affecting the cyclase.1 These persistent P-receptors may be "uncoupled", since their affinity for isoproterenol is reduced.64 Possibly, the step from uncoupled receptors to actual disappearance of NE receptors is interrupted by the loss of 5-HT input. An interesting corollary is the observation that depressed patients benefiting from either imipramine or tranylcypromine showed... 

The pressor effects of intravenous infusions of noradrenaline were increased four to eightfold, of adrenaline two to fourfold, and of phenylephrine two to threefold in 4 healthy subjects who had been taking imipramine 75 mg daily for 5 days. There were no noticeable or consistent changes in their response to isoprenaline (isoproterenol). However, in a study of possible adverse interactions between imipramine and isoprenaline, although no abnormalities of heart rhythm were seen, one out of the 4 healthy subjects studied showed potentiation of isoprenaline- induced tachycardia. ... 

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