A quantitative study of the anticholinergic action of several tricyclic antidepressants on the rat isolated fundal strip

1. Investigations were carried out on the antagonism of the action of carbamylcholine chloride on the isolated fundus of the rat stomach by several tricyclic antidepressants.2. The anticholinergic potency of the compounds was in the order: GP 45437>amitriptyline>protriptyline>desmethylimipramine>opipramol. All of the antagonists were less effective than atropine.3. Statistical analysis was carried out to determine whether the theory of competitive antagonism would fit the data obtained.

The effect of -phenethylamine upon spontaneous motor activity in mice: a dual effect on locomotor activity

The effect of intraperitoneal injections of β-phenethylamine on spontaneous motor activity in mice has been examined. Doses 75 mg/kg and higher produced a biphasic type of activity. A first phase of increased activity occurred about 5 min after injection, and a second about 30 min after injection. Pharmacological examination of these curves showed the first peak to be an indirect effect requiring newly synthesized noradrenaline, while the second peak appeared to be caused by a direct action. Thus it was not affected by reserpine, α-methyldopa, protriptyline, desipramine, disulfiram or α-methyl-p-tyrosine. These results suggest that phenethylamine differs from amphetamine in its effect on spontaneous motor activity.

Central effects of 6-hydroxydopamine on the body temperature of the rat

1. Rats which had been pretreated with intraventricular injections of 6-hydroxydopamine (6-OHDA) to cause a selective depletion of brain noradrenaline (NA) to 20.7% of control brain NA and brain dopamine (DA) to 34.6% of control brain DA retained an unimpaired ability to regulate their body temperatures on exposure to heat or cold. This is discussed in relation to the possible role of brain NA in the central control of body temperature.2. Intraventricular injections of 6-OHDA in normal rats at room temperature caused an acute, dose dependent hypothermia of up to 4.5 degrees C which lasted for 4-5 hours. Depletion of brain NA and DA by prior treatment with 6-OHDA markedly reduced the hypothermic response to a subsequent dose of 6-OHDA. Selective depletion of brain NA without affecting brain DA did not reduce the response to 6-OHDA. The acute hypothermic response to 6-OHDA, may therefore, be related to a release of DA in the brain.

Interactions of inhibitors of noradrenaline uptake and angiotensin on the sympathetic nerves of the isolated rabbit heart

1. The interaction of angiotensin and several inhibitors of the uptake of noradrenaline across the neuronal membrane (cocaine, desipramine, protriptyline. and pronethalol) on the output of noradrenaline produced by sympathetic nerve stimulation has been studied in the isolated perfused rabbit heart.2. Most of these drugs increased noradrenaline outflow-angiotensin, for example, by 175%. Cocaine (10(-4)M) did not change the amine overflow, probably because this very high concentration inhibited not only the re-uptake but also the liberation of noradrenaline.3. Desipramine, protriptyline, and pronethalol, although infused in concentrations which enhanced the noradrenaline output, were not able to impair the angiotensin-induced increase of transmitter overflow. In the presence of cocaine (10(-4)M) the increase elicited by angiotensin was slightly reduced, though lower concentrations of cocaine, as previously described, do not interfere with the effect of angiotensin.4. In contrast to the interaction between uptake inhibitors and angiotensin, the augmented output of noradrenaline caused by an uptake inhibitor could not be increased further by infusion of a second uptake inhibitor.5. It is concluded that the increase of the outflow of noradrenaline during sympathetic nerve stimulation by small doses of angiotensin is not caused by an inhibition of re-uptake. On the contrary, the transmitter liberation seems to be facilitated. This is a novel principle of drug action on the sympathetic nerve terminals.

The interactions of noradnamine and imipramine-like antidepressant drugs

1. The hypothesis of Roberts & Broadley (1965) that noradnamine formation in the brain is responsible for endogenous depression has been investigated in mice.2. Injections of noradnamine given directly into the lateral ventricles caused convulsions and profound hypothermia, but were without effect if given subcutaneously.3. The hypothermia, but not the convulsions, induced by noradnamine was reversed by imipramine-like antidepressant drugs given before or after the injection of noradnamine. The convulsions but not the hypothermia were abolished by phenobarbitone.4. Increasing doses of nortriptyline produced a parallel shift of the hypothermic log dose-response curve for intraventricular injections of noradnamine to the right.5 The minimal effective dose of nortriptyline required to reverse noradnamine hypothermia was the same whether the nortriptyline was injected directly into the lateral ventricle or subcutaneously.6. No evidence was found to substantiate the claim that reserpine hypothermia is mediated by noradnamine formation in the brain.7. Intraventricular, but not intraperitoneal, injection of noradnamine caused a depletion of brain noradrenaline and an increase in brain 5-hydroxytryptamine. These changes did not result from the convulsive activity and were not modified by pretreatment with nortriptyline. No effect on heart noradrenaline levels was recorded.8. Noradrenaline, given subcutaneously, also antagonized the hypothermic response to noradnamine.9. The reversal of noradnamine hypothermia by both noradrenaline given subcutaneously and nortriptyline was blocked by alpha and beta-adrenoceptive receptor blocking agents.10. It is considered that the mode of action of the antagonism of noradnamine hypothermia by imipramine-like antidepressant drugs is a peripheral and not a central mechanism and probably results from a potentiation of the effects of circulating noradrenaline released by noradnamine.