Brain levels of imipramine and desipramine after combined treatment with these drugs in rats

A Comparative Study on Desipramine Pharmacokinetics in the Rat Brain after Administration of Desipramine or Imipramine

Chronic intraperitoneal administration of desipramine led to an extensive cumulation of the drug in brain and blood compared with that after a single dose treatment, while chronic treatment with desipramine by the oral route produced a brain concentration comparable with its level after a single oral dose. Comparison of the present results with the corresponding data of published imipramine pharmacokinetics indicated that the cumulation of desipramine in the rat brain was nearly the same when rats received desipramine or imipramine twice a day for two weeks at a dose of 10 mg kg−1 orally, or imipramine, twice a day for two weeks at a dose of 10 mg kg−1 intraperitoneally. It is suggested that these three experimental paradigms may be used as models for differentiation of the pharmacological effects of imipramine and desipramine in-vivo.

Studies on the preparation, characterization and pharmacological evaluation of tolterodine PLGA microspheres

In this study, poly(d,l-lactide-co-glycolide) (PLGA) microspheres of tolterodine depot formulation were prepared using oil in water (o/w) method to investigate their potential pharmacokinetic and pharmacodynamic advantages over tolterodine l-tartrate tablets. Morphological studies of the microspheres showed a spherical shape and smooth surface with mean size of 50.69-83.01 microm, and the encapsulation efficiency was improved from 62.55 to 79.10% when the polymer concentration increased from 180 to 230 mg/ml. The addition of stearic or palmitic acids could significantly raise the drug entrapment efficiency but only slightly affected the in vitro release. A low initial burst followed by a proximately constant release of tolterodine was noticed in the in vitro release profiles. The in vivo study was carried out by intramuscular (i.m.) administration of tolterodine-loaded microspheres on beagle dogs, and a sustained release of drug from the PLGA microspheres was achieved until the 18th day with a low initial burst. Since the absence of hepatic first pass metabolism, only a single active compound-tolterodine was detected in the plasma. This avoided the coexistence of two active compounds in plasma in the case of oral administration of tolterodine, which may lead to a difficulty in dose control due to the different metabolic capacity of patients. In the pharmacodynamic study, the influence of tolterodine PLGA microspheres on the inhibition of carbachol-induced rat urinary bladder contraction was more significant than that of tolterodine l-tartrate tablets. There were invisible changes in rat bladder slices between tolterodine-loaded PLGA microspheres group and tolterodine l-tartrate tablets group. These results indicate that the continuous inhibition of muscarinic receptor may offer an alternative therapy of urge incontinence.

Opioid peptides and receptors in relation to affective illness. Effects of desipramine and lithium on opioid receptors in rat brain

A brief review is given of clinical and experimental evidence supporting the notion that opioid peptides and opioid receptors play a role for the regulation of mood and activity, and that they could be involved in the pathophysiology of affective illness and the action of antimanic and antidepressant treatment modalities. We have carried out in vitro and in vivo studies on the effects of desipramine and lithium on opioid receptors in rat brain. In vitro desipramine inhibited the binding of 3H-enkephalinamide to neuronal membranes (P2-fractions) through mechanisms not yet known. Treatment with desipramine in vivo (10 mg/kg body weight/day) caused a down-regulation of 3H-enkephalinamide binding in the basal ganglia and the hippocampus, while no effects could be observed in the cerebral cortex and the rest of the forebrain. In vitro addition of lithium inhibited enkephalin binding to opioid receptors through a reduction in the number of binding sites, while the affinity remained unchanged or was changed only slightly. Treatment with lithium in vivo for three weeks with lithium doses providing serum lithium concentrations of about 1 mM also caused a down-regulation in the number of opioid binding sites in the cerebral cortex, the hippocampus, and the basal ganglia, while no changes could be observed in affinity. The studies suggest that desipramine and lithium, both effective in the treatment of manic-depressive illness, may share certain actions on opioid receptors in the brain.

Design of a desipramine dosing regimen for the rapid induction and maintenance of maximal cortical beta-adrenoceptor downregulation

Chronic administration of desipramine to rats causes a gradual reduction in cortical beta-adrenoceptor density. We examined the relationship between the duration of treatment with desipramine, and the rate and intensity of cortical beta-adrenoceptor downregulation. Male Sprague-Dawley rats were administered a 3.75 mg/kg/12 hr dose of desipramine for 4, 8 or 16 days. After 4 and 8 days of treatment, cortical beta-adrenoceptor density was reduced by 14 and 26% respectively. After 16 days of treatment, cortical beta-adrenoceptor density was maximally reduced by 36%. In our next series of experiments, we tested the hypothesis that the dose of desipramine required to rapidly induce maximal beta-adrenoceptor downregulation was higher than the dose required to maintain maximal beta-adrenoceptor downregulation. Initially, cortical beta-adrenoceptors were rapidly, and maximally downregulated with a four day, 10 mg/kg/12 hr induction regimen of desipramine. Trough, steady-state brain/cortical concentrations of desipramine plus desmethyldesipramine at the end of this regimen were approx 4000 ng/gm. Subsequently, maintenance desipramine regimens of 3.75 mg/kg/12 hr and 1.87 mg/kg/12 hr or vehicle were initiated for the next four days. Inspite of a 20-fold drop in brain/cortical concentrations of desipramine plus its metabolite, the 3.75 mg/kg maintenance regimen sustained maximal cortical beta-adrenoceptor downregulation. The 1.87 mg/kg maintenance regimen did result in a marked (25%) but non-significant recovery in the density of beta-adrenoceptors. Animals administered a vehicle maintenance regimen showed a large (50%) and statistically significant recovery of cortical beta-adrenoceptor density.

Opioid receptors in the brain of the rat following chronic treatment with desipramine and electroconvulsive shock

The effect of chronic administration of electroconvulsive shock and the antidepressant drug desipramine on binding to opioid receptors was studied in the cerebral cortex, the basal ganglia and the hippocampus of the forebrain of the rat. In vitro, desipramine inhibited the binding of enkephalinamide to opioid receptors through a reduction in the number of binding sites, whereas the affinity was unchanged or only slightly decreased. In vivo desipramine, injected daily (10 mg/kg) for three weeks, did not change the number of opioid binding sites in the forebrain of the rat. Chronic electroconvulsive shock, given twice a week for three weeks, had no effect on the number of opioid binding sites in the forebrain of the rat. The data do not support the hypothesis of shared effects of lithium, tricyclic antidepressants and electroconvulsive shock on the opioid peptide-opioid receptor systems.

Potentiation of the action of adenosine on cerebral cortical neurones by the tricyclic antidepressants

The effects of four tricyclic antidepressants, nortriptyline, iprindole, chlorimipramine and desipramine on adenosine-evoked depressions of the firings of rat cerebral cortical neurones has been studied. When applied iontophoretically, all four substances enhanced the depressant actions of iontophoretically applied adenosine but did not affect the depressant actions of the uptake-resistant analogue, adenosine 5'-N-ethylcarboxamide (NECA). Nortriptyline and iprindole administered intravenously (1 mg kg-1) enhanced the depressant actions of iontophoretically applied adenosine. When applied by larger iontophoretic currents, all four antidepressants inhibited the firing of cerebral cortical neurones. Chlorimipramine- and desimipramine-elicited depressions were antagonized by intravenously administered caffeine, an adenosine antagonist. Earlier studies showed the tricyclic antidepressants inhibit the uptake of adenosine by rat brain cerebral cortical synaptosomes. The present results demonstrate that four antidepressants are able to potentiate the action of adenosine and that this occurs when these compounds are given in behaviourally meaningful doses. The specificity of the potentiation is demonstrated by the failure of these compounds to potentiate the depressant actions of an uptake-resistant analogue of adenosine, NECA. Antagonism of the inhibitory effects of the antidepressants on neuronal firings by caffeine, indicates that these compounds can enhance the extracellular levels of endogenously released adenosine sufficiently to depress cell firing.

Artefactual inhibition of dopamine uptake by psychotropic drugs on striatal synaptosomal preparation

On striatal synaptosomal preparations, using a double labelling test, numerous antidepressant drugs demonstrated an inhibitory effect on [3H]DA uptake at the same high concentrations producing a [14C]DA release. This releasing effect was also shared by non-antidepressant agents and was observed on synaptosomes preloaded with [3H]5HT. The imipramine-induced release of DA was not modified by increasing concentration of K+, by decreasing concentration of Na+, by deleting Ca2+ from the incubation medium, or by blocking the catecholamine uptake systems with nomifensine or cocaine. The imipramine effect was reversible and was possibly initiated by a transient physico-chemical modification of the synaptosomal membrane. It was concluded that the DA uptake carrier is probably not involved in the effect of these drugs.

Dopamine and depression: a review of recent evidence. III. The effects of antidepressant treatments

This paper reviews the effects of antidepressants on brain dopamine (DA) function in people and animals. Acute antidepressant treatments have no consistent effect on DA. Chronic treatment does not appear to change DA synthesis or turnover, or to affect post-synaptic DA receptors. However, there is considerable evidence of increased DA function following chronic antidepressant treatments; the site of these effects is at present unclear, but appears to be beyond the DA receptors. There is also evidence for decreased sensitivity of pre-synaptic DA autoreceptors, though this effect is less well established.

Relationships between brain concentrations of desipramine and paradoxical sleep inhibition in the rat

Desipramine (DMI), like many antidepressant drugs, inhibit the production of paradoxical sleep (PS). In the present experiment, we have investigated the relationships between brain level of DMI and PS inhibition. Groups of rats had their sleep monitored after 1, 2 or 4 mg/kg of DMI. In other animals, the brain concentration of DMI was assayed at various times after the same treatments. The results indicate that a critical threshold concentration of 300 ng/g DMI in the brain is necessary for complete PS inhibition. This stage reappears only when the DMI level falls below this value, and its production resumes at a normal rate, provided the DMI level reached initially was not largely in excess of the threshold concentration. The results are discussed with regard to the present knowledge of specific binding of tricyclics in brain and their "ex vivo" action on norepinephrine uptake resulting in enhancement of collateral inhibiton of noradrenergic cells.

Inhibition of (3H)-dopamine uptake into rat brain synaptosomes by the new non-tricyclic antidepressants, FS32 and FS97

The effects of new non-tricyclic antidepressants, FS32 and its desmethylated compound (FS97), on the uptake of (3H)-dopamine (DA) by rat purified whole brain synaptosomes and the striatal synaptosomes were studied. The uptake into synaptosomes was time- and temperature-dependent and was saturable with a Km value of 9.1 X 10(-8) M. The inhibiting activities of both compounds were comparable to those of amitriptyline, nortriptyline and iprindole, and were nearly twice the activity of imipramine and desipramine. The kinetic constants indicated that both FS32 and FS97 were competitive inhibitors of (3H)-DA uptake. Neither drug caused a significant release of (3H)-DA from the synaptosomes.

The in vivo distribution of an antidepressant drug (DMI) in male and female rats

The accumulation of IP injected 3H-desipramine (DMI) in the brain and in the liver has been studied in both male and female rats. The total amount of DMI in the brains of females is 2 to 4 times that found in the brains of males. In females the amount of DMI is highest on the day of estrus and lowest on proestrus. This sex difference was not found following the injections of another psychoactive drug, 3H-chlorpromazine. In both males and females the level of DMI in the cortex and caudate is slightyl higher than in the hippocampus, septum and hypothalamus. The pharmaco-kinetics and dose dependence of the accumulation of DMI are also similar in males and females. Maximal levels are reached in the liver in less than 15 min, whereas in the brain it takes 30 min. The decline of radioactivity in the liver is faster than in brain. There is no saturation in the amount of DMI taken in brain. There is no saturation in the amount of DMI taken up in brain or liver in the dose range up to 40 mg/kg. The sex difference in the amount of 3H-DMI in brain, which may be the result of sex-dependent metabolism in liver microsomes, may explain the male-female differences in reaction to antidepressants.

Metabolism of 5-hydroxytryptamine and levels of tricyclic antidepressant drugs in rat brain after acute and chronic treatment

Because tricyclic antidepressants (TAD) are usually given chronically to patients, both their acute and their chronic effects on 5-hydroxytryptamine (5-HT) metabolism were studied. The probenecid method was used and, in addition to 5-hydroxy-indoleacetic acid (5-HIAA), some other indole compounds in brain were measured. Simultaneously, TAD levels in brain and plasma were determined. Dimethylated as well as monomethylated TADs were administered, both at 10 and 25 mg/kg i.p. Treatment with either 10 mg/kg during 14 days or 25 mg/kg given acutely resulted in a similar brain level of TAD, so any differences found could be attributed to differences in administration schedule. Drug levels in brain and plasma differed considerably after chronic and acute treatments but no major differences in the effect on 5-HIAA level in the brain were found, although accumulation of 5-HIAA following probenecid treatment was mostly lowered after treatment with dimethylated TAD. The TAD level in rat brain was not decisive for the effect on central 5-HT turnover. The monomethylated TAD affected the 5-HT turnover very little, not only acutely but also chronically.

Blood and brain concentrations of imipramine, clomipramine and their monomethylated metabolites after oral and intramuscular administration in rats

Imipramine and clomipramine were administered to rats by the oral and intramuscular routes as single and multiple doses. The concentrations of both drugs and their active demethylated metabolites desipramine and desmethylclomipramine were measured in blood plasma, blood cells and brain. The concentrations of the metabolites were higher and the concentrations of the parent substances lower after oral than after parenteral administration, both in blood and in brain. In brain imipramine, despiramine and clomipramine during continuous treatment exceeded their plasma concentrations by six to ten times. The corresponding figure for desmethylclomipramine was 1-7. The extent of accumulation of the investigated substances in the brain was independent of the route of administration.