Assessment of genomic instability in normal and diabetic rats treated with metformin.

To examine if a single or multiple oral administration of metformin, a member of the biguanide class of anti-diabetic agents, has any genotoxic and cytotoxic potential in normal and diabetic rats, a mammalian model, cytogenetic assays through several endpoints such as induction of micronuclei, chromosome aberrations, mitotic activity of bone marrow cells, sperm-head anomaly and assays of some oxidative stress markers have been conducted by the use of standard techniques. Diabetes was induced by streptozotocin injection. Metformin was administrated to both diabetic and non-diabetic rats in single doses of 100, 500 or 2500 mg/kg along with vehicle control groups for diabetic and non-diabetic rats. The animals were killed by cervical dislocation at 24h after treatment, and then bone marrow cells were sampled. Also, a multiple dose study has done in which diabetic and non-diabetic animals were treated with 100 or 500 mg/kg of metformin daily for 4 or 8 weeks after which the animals were killed by cervical dislocation, and then bone marrow and sperm cells were collected. Concurrent control groups were also included in each experiment. The obtained results revealed that metformin was neither genotoxic nor cytotoxic for the rats in all groups at all tested doses. Moreover, metformin significantly reduced the diabetes-induced genomic instability and cell proliferation changes in somatic and germinal cells in a dose-dependent manner (2500, 500, >100mg/kg). In addition, diabetes induced marked biochemical alterations characteristic of oxidative stress including, enhanced lipid peroxidation and reduction in the reduced glutathione level. Treatment with metformin ameliorated these biochemical markers. In conclusion, metformin is a non-genotoxic or cytotoxic compound and may protect from genomic instability induced by hyperglycemia. Apart from its well-known anti-diabetic effect, the antigenotoxic effect of metformin could be possibly ascribed to its radical scavenger effect that modulated the genomic instability responses and cell proliferation changes induced by hyperglycemia.

Protection of gastric mucosal damage by Coriandrum sativum L. pretreatment in Wistar albino rats.

The effect of Coriander pretreatment on gastric mucosal injuries caused by NaCl, NaOH, ethanol, indomethacin and pylorus ligation accumulated gastric acid secretions was investigated in rats. Pretreatment at oral doses of 250 and 500mg/kg, body weight was found to provide a dose-dependent protection against the (i) ulcerogenic effects of different necrotizing agents; (ii) ethanol-induced histopathological lesions; (iii) pylorus ligated accumulation of gastric acid secretions and ethanol related decrease of Nonprotein Sulfhydryl groups (NP-SH). Results obtained on the study of gastric mucus and indomethacin-induced ulcers demonstrated that the gastro protective activity of Coriander might not be mediated by gastric mucus and/or endogenous stimulation of prostaglandins. The protective effect against ethanol-induced damage of the gastric tissue might be related to the free-radical scavenging property of different antioxidant constituents (linanool, flavonoids, coumarins, catechins, terpenes and polyphenolic compounds) present in Coriander. The inhibition of ulcers might be due to the formation of a protective layer of either one or more than one of these compounds by hydrophobic interactions.

Reduction of elevated arterial blood pressure in obese Zucker rats by inhibition of ganglionic long-term potentiation.

Sustained enhancement of the basal tone of ganglionic transmission is expected to result in an enduring increase in peripheral resistance that would lead to elevated blood pressure. Long-term potentiation of sympathetic ganglia is an activity-dependent long-lasting increase in strength of ganglionic transmission. Therefore, ganglionic long-term potentiation might be involved in the manifestation of neurogenic forms of hypertension. Expression of sympathetic ganglionic long-term potentiation is dependent on activation of 5-HT(3) receptor. We examined the possibility that elevated blood pressure in obese Zucker rat, which is reported to be stress-prone, might be partly due to a neurogenic factor resulting from expression of ganglionic long-term potentiation. Chronic treatment with the 5-HT(3) receptor antagonist ondansetron (0.5 mg/kg/day) caused a significant decrease in blood pressure of the obese Zucker rats without affecting that of normotensive lean Zucker rats. Electropysiological procedures to test for long-term potentiation in isolated ganglia suggest that ganglionic long-term potentiation has been previously expressed in vivo in ganglia from obese Zucker rat but not in those from the normotensive lean Zucker rats. The results indicate that expression of ganglionic long-term potentiation in sympathetic ganglia may be responsible for neurogenic increase in blood pressure, which contributes to the moderate hypertension often seen in the obese Zucker rats.

Effect of short-term use of different non-steroidal anti-inflammatory drugs on renal function during fasting in ramadan.

This study was conducted to determine the combined effect of Ramadan fasting and short-term use of different non-steroidal anti-inflammatory drugs (NSAIDs) on renal function in healthy volunteers. The study subjects were assigned to six different groups, five of whom took different NSAIDs (namely nabumetone, indomethacin, diclofenac, sulindac, tenoxicam) and the sixth was a control group. Data were collected on serum sodium, chloride, potassium, urea, creatinine, bicarbonate and uric acid as well as urinary osmolarity, sodium, potassium, chloride and urea. These measurements were taken before fasting, 10 days into fasting while using NSAIDs, and five days after stopping the use of NSAIDs. The results showed slight changes in serum and urine measurements during fasting while using NSAIDs. These changes, although were significant in some cases, were within the normal range and were noted in all the study groups including the control group. We conclude that short-term use of NSAIDs in healthy subjects during fasting is not associated with any major adverse effects on the renal function.

The quipazine- and TFMPP-increased conditioned avoidance response in rats: role of 5HT1C/5-HT2 receptors.

The role of serotonin (5-HT) in the acquisition of the conditioned avoidance response was investigated. The effects of different serotonin agonists and antagonists, administered prior to learning sessions, were studied in groups of naive rats using the two-way shuttle box. Quipazine, an agonist at 5-HT1B/1C/2 receptors, significantly increased avoidance responding in a dose-dependent manner (1.25-10 mg/kg, s.c.). The putative 5-HT1B/1C receptor agonist TFMPP (1-[m-trifluoromethylphenyl] piperazine) at doses of 1.25 and 2.5 mg/kg (s.c.), increased acquisition of conditioned avoidance but showed no significant difference from control at doses of 5 and 10 mg/kg. The 5-HT1A agonist, buspirone, significantly decreased acquisition of conditioned avoidance. Increased acquisition of conditioned avoidance induced by either quipazine or TFMPP was effectively antagonized by the mixed 5-HT 1C/2 receptor antagonists, ketanserin (0.2 and 2 mg/kg, s.c.) and mianserin (1 mg/kg, s.c.). In contrast, spiperone (5-HT1A/2 receptors antagonist: 0.2 mg/kg, s.c.) only inhibited the increased acquisition induced by TFMPP. On the other hand, the 5-HT1A/1B receptors antagonist, pindolol, failed to antagonize the increase in acquisition of conditioned avoidance caused by quipazine or TFMPP. These results suggest that quipazine increases the conditioned avoidance behaviour by an action that might be mediated through stimulation of 5-HT1C receptors. The acquisition of conditioned avoidance induced by TFMPP, which was blocked by ketanserin, mianserin and spiperone but not by pindolol, suggests the involvement of 5-HT1C/2 receptors in the action of TFMPP.

Intrathecal 5-methoxy-N,N-dimethyltryptamine in mice modulates 5-HT1 and 5-HT3 receptors.

The antinociceptive effects of intrathecally administered 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT), a potent 5-HT receptor agonist, were studied in three behavioral tests in mice: the tail-flick test and the intrathecal substance P and N-methyl-D-aspartic acid (NMDA) assays. Intrathecal administration of 5-MeO-DMT (4.6-92 nmol/mouse) produced a significant prolongation of the tail-flick latency. This action was blocked by 5-HT3 and gamma-aminobutyric acidA (GABAA) receptor antagonists but not by 5-HT2, 5-HT1A, 5-HT1B or 5-HT1S receptor antagonists. Binding studies indicated that 5-MeO-DMT had very low affinity for 5-HT3 receptors. 5-MeO-DMT inhibited biting behavior while increasing scratching behavior induced by intrathecally administered substance P. The inhibition of biting behavior was antagonized by intrathecal co-administration of 5-HT1B and GABAA receptor antagonists while 5-HT1A, 5-HT1S, 5-HT2 and 5-HT3 receptor antagonists had no effect. 5-MeO-DMT-enhanced scratching behavior was inhibited by all the antagonists used except ketanserin and bicuculline, suggesting the involvement of 5-HT1A, 5-HT1B, 5-HT1S, 5-HT3 and GABAA receptors. NMDA-induced biting behavior was inhibited by 5-MeO-DMT pretreatment; this action was antagonized by 5-HT1B, 5-HT3 and GABAA receptor antagonists. The involvement of these receptors in 5-MeO-DMT action suggests that it may promote release of 5-HT (5-hydroxytryptamine, serotonin).

Anticholinergic, antihistaminic and cardiovascular effects of two new congeners of quipazine and trazodone.

Two recently reported analogues of quipazine (CAS 4774-24-7) and trazodone (CAS 19794-93-5) were found to be selective inhibitors of 5-hydroxytryptamine (5-HT) uptake, with an antidepressant profile similar to the atypical antidepressants. In the present work the anticholinergic, antihistamine and cardiovascular effects of the compounds were investigated in experimental animals and compared with imipramine and trazodone. Both compounds have demonstrated weak anticholinergic and antihistamine activities on the guinea-pig ileum and showed weak negative inotropic effects on the isolated rabbit heart as compared to imipramine. The marked bradycardia produced by imipramine and trazodone, and the extrasystoles produced by imipramine were not produced by either compound. Binding studies at 5-HT receptors indicated that the quipazine analogue, compound I, has moderate affinity for the selective 5-HT1D ligand while the trazodone analogue, compound II, binds to 5-HT2 receptors. Structural modifications of these compounds may offer new potent analogues with selective affinity at 5-HT receptor-subtypes.

Differential effects of fluoxetine on isoprenaline-stimulated water intake in ethanol-treated rats: a role for beta-adrenoceptors.

We examined the effects of subchronic (4 days) administration of the 5-hydroxytryptamine (5-HT) re-uptake inhibitors, fluoxetine, fluvoxamine and zimelidine and the noradrenaline-uptake inhibitor, desipramine, on isoprenaline-induced water drinking in rats treated with ethanol. These rats demonstrated significant increases in water drinking as compared to control rats that had received only i.p. injections of distilled water (P < 0.01). Administration of fluoxetine (5-20 mg/kg daily i.p., for 4 days) dose-dependently decreased water intake as compared to that of rats treated with ethanol only. In contrast, fluvoxamine, zimelidine (10 mg/kg i.p.) and desipramine (5 mg/kg i.p.) produced no significant effects on water intake. Pretreatment of animals with spiperone, methysergide, ritanserin, zacopride and BRL 43694A, together with fluoxetine, failed to reverse the inhibitory effect of the latter on isoprenaline-stimulated water intake. The results of the present study indicate that the action of fluoxetine on isoprenaline-stimulated water drinking in ethanol-treated rats may be mediated by an action on beta-adrenoceptors.

Differential roles of 5-hydroxytryptamine1A and 5-hydroxytryptamine1B receptor subtypes in modulating spinal nociceptive transmission in mice.

The modulatory effect of spinal serotonin (5-HT)1 receptors on nociception was studied in mice. 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and buspirone, putative 5-HT1A agonists, m-trifluoromethylphenyl-piperazine (TFMPP) and 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo(1,2-1a)quinoxaline (CGS 12066B), 5-HT1B agonists, and 5-carboxamidotryptamine (5-CT), a mixed 5-HT1A and 5HT1B agonist, were used. Intrathecal administration of 8-OH-DPAT, buspirone and 5-CT (1-12 nmol/mouse) significantly facilitated the tail-flick reflex, whereas TFMPP and CGS 12066B prolonged tail-flick latency. When administered i.t. after s.c. pretreatment (25 min) with morphine sulfate, 8-OH-DPAT, buspirone and 5-CT shifted the morphine sulfate dose-response curve 3- to 5-fold to the right. Spiperone, propranolol and pindolol (mixed 5-HT1A and 5-HT1B antagonists) effectively reversed both the tail-flick facilitation and the antagonistic effect on morphine sulfate-induced antinociception produced by 8-OH-DPAT and 5-CT. In addition, simultaneous i.t. administration of 8-OH-DPAT with substance P or N-methyl-D-aspartic acid decreased biting but increased scratching behavior, an effect which is also blocked by the 5-HT1 antagonists. These results confirm and extend other reports on the facilitory role of 5-HT1A receptor subtype on nociceptive responses and support the involvement of 5-HT1B receptor subtype in the antinociceptive action of serotonin.

New hybrids of quipazine and trazodone as selective inhibitors of uptake of 5-hydroxytryptamine.

Two new congeners, 4-(chloropropyl)-1-(2-quinolyl)piperazine- and 2-[3-[4-[2-(quinolyl)]-1-piperazinyl]propyl]-1,2,4-triazolo] 4,3-a]pyridin-3(2H)-one, of trazodone were synthesized and found to be potent and selective inhibitors of synaptosomal uptake of 5-hydroxytryptamine [5-HT, serotonin; IC50 = norepinephrine greater than 5 microM, 5-HT = 210-890 nM], with minimal effects in antagonizing (-)-apomorphine-induced climbing behavior and suppression of spontaneous locomotor activity in mice (ED50 greater than 50 mg/kg). The two compounds behaved like atypical antidepressants, since they weakly antagonized reserpine-induced hypothermia. The acute toxicity studies have shown that these compounds were less lethal when compared with imipramine or quipazine. Furthermore, chronic treatments (20 mg/kg, daily for 10 and 21 days) significantly decreased the isoprenaline-induced increase in cyclic AMP in the rat brain cortex, suggesting desensitization of beta-adrenoceptors. These findings point to the effects of these compounds as potential antidepressants dealing with specific serotonergic mechanisms.

Spinal 5-HT3 receptor-mediated antinociception: possible release of GABA.

Although 5-HT is clearly involved in spinal analgesia, its mode of action remains obscure, perhaps because it has multiple and often opposing effects mediated by its multiple receptor subtypes. This investigation uses selective agonists and antagonists directed at the most recently defined class of 5-HT receptors (5-HT3 receptors) in behavioral and electrophysiological studies of nociception in the spinal cord of rodents. The results demonstrate uniformly inhibitory effects of a selective 5-HT3 agonist on responses to noxious stimuli. Intrathecally administered 2-methyl 5-HT produced dose-dependent antinociception in the tail-flick test and inhibited behaviors elicited by intrathecally administered agonists for excitatory amino acid and neurokinin receptors, namely NMDA and substance P (SP). All 20 dorsal horn neurons we examined, which projected to the brain and responded to both noxious stimuli and NMDA, were inhibited in a current-related manner by this 5-HT3 agonist applied iontophoretically. Both the behavioral and electrophysiological effects were blocked not only by the 5-HT3 antagonists zacopride and ICS 205-930, but also by antagonists to the inhibitory amino acid GABA. Therefore, 5-HT via an action at 5-HT3 receptors may evoked release of GABA, which may in turn inhibit nociceptive transmission at a site postsynaptic to terminals of primary afferent fibers. If the descending serotonergic analgesic system in humans operates similarly, understanding it may enable the development of new nonopioid, nonaddictive analgesics.

Antinociceptive effect of ketanserin in mice: involvement of supraspinal 5-HT2 receptors in nociceptive transmission.

The involvement of 5-HT2 receptors in pain transmission was investigated in mice. Subcutaneous administration of the selective 5-HT2 receptor antagonist ketanserin produced dose-dependent antinociception in the hot-plate and acetic acid-induced writhing tests with ED50 values (95% confidence limit) of 1.51 (1.13-1.89) and 0.62 (0.10-1.40) mg/kg, respectively, but was without any significant effect on the tail-flick test. Pretreatment with the catecholamine depletors 6-hydroxydopamine (2.5 micrograms, i.c.v.) or alpha-methyl-p-tyrosine (200 mg/kg, s.c.), or the serotonin synthesis inhibitor p-chlorophenylalanine methylester (200 mg/kg, s.c.), resulted in a significant decrease in the antinociceptive effect of ketanserin. Likewise, intrathecal (i.t.) administration of 1 microgram/mouse of idazoxan (an alpha 2-antagonist), methysergide (mixed 5-HT1, and 5-HT2 antagonist) or ketanserin also reversed the antinociceptive effect of s.c. administered ketanserin. The results of this work indicate that 5-HT2 receptors located supraspinally may inhibit descending nociceptive neurotransmission. In addition, these studies suggest that 5-HT2 receptors located at the spinal level modulate nociception.

Enhancement of imipramine-induced rat brain beta-adrenoreceptor desensitization by subacute co-administration of trazodone, zimelidine, quipazine or 5-hydroxytryptophan.

The present work was undertaken to characterize the role of serotonin in the regulation of beta-adrenoceptors utilizing isoprenaline-induced water drinking in the rat. For this purpose, a serotonin precursor, 5-hydroxytryptophan (24.3 mg/kg/day, PO), the serotonin neuronal uptake blockers, trazodone (18.5 mg/kg/day, PO), or zimelidine (14.6 mg/kg/day, PO) or a serotonin agonist, quipazine (12.6 mg/kg/day, PO) were administered either alone or in combination with imipramine for a period of 4 days. While none of these drugs alone showed any significant effect in attenuating the effects of isoprenaline-induced water drinking, their co- administration with imipramine did produce a significant reduction in isoprenaline-induced drinking. Simultaneous injection of the serotonin synthesis inhibitor, p-chlorophenylalanine (200 mg/kg/day, IP), has resulted in blockade of this acceleration of desensitization of beta-adrenoceptors produced by the subacute co-administration of trazodone or quipazine with imipramine. The selective 5HT2 receptor antagonist ketanserin (4 mg/kg/day/ IP) significantly inhibited the attenuation of the isoprenaline-induced drinking attained by the co-administration of quipazine with imipramine, while methysergide (2 mg/kg/day, IP) which blocks both 5HT1 and 5HT2 receptors failed to produce a significant effect on this response. These results indicate that the inhibition of the synaptosomal uptake of serotonin by quipazine seems to be more pertinent than its serotoninergic agonistic effect in the desensitization of central beta-adrenoceptors in the rat. Thus, it can be concluded that noradrenaline and serotonin are both required for the process of the desensitization of central beta-adrenoceptor systems by antidepressants.

Antinociceptive and anti-inflammatory activity of a novel quipazine derivative (AAL-13): a selective inhibitor of 5-hydroxytryptamine reuptake.

The anti-inflammatory and antinociceptive activities of a novel quipazine derivative 2(4-(3-chloropropyl)piperazinyl) quinoline (AAL-13), a selective inhibitor of 5-hydroxytryptamine (5-HT) reuptake, has been examined. Anti-inflammatory activity was assessed by mesuring the inhibition of a cotton pellet granuloma and of carrageenan-induced paw oedema in rats, and of cantharidin-induced topical inflammation in the mouse ear. Antinociceptive activity was studied by using the modified Randall-Selitto method. Indomethacin was used as a reference. AAL-13 slightly inhibited granuloma formation (13%, P less than 0.02) at 100 mg kg-1 day-1 for 7 days, whereas half that dose had no significant effect. There was significant inhibition of carrageenan-induced rat paw oedema (35%, P less than 0.05 and 103%, P less than 0.001) 3 h after single doses of AAL-13 (50 and 100 mg kg-1 p.o., respectively). Three hours after i.p. injection, the oedema inhibition was 58% (P less than 0.05) and 86% (P less than 0.001) for doses of 25 and 50 mg kg-1, respectively. In comparison, indomethacin (3, 6 and 12 mg kg-1 p.o.) inhibited oedema by 59% (P less than 0.02), 65% (P less than 0.01) and 63% (P less than 0.02), respectively. Intraperitoneally, only the 12 mg kg-1 dose produced significant inhibition (82%, 3 h after carrageenan injection, P less than 0.05). AAL-13 (1.5 mg/ear) had a significant anti-inflammatory effect on the mouse ear (52%, inhibition, P less than 0.05), while indomethacin (3 mg/ear) gave 43% inhibition (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of ventricular arrhythmias resulting from acute coronary artery ligation in rat by imipramine.

The potential antiarrhythmic activity of imipramine against ventricular arrhythmias induced by coronary artery ligation in rats has been investigated and compared with procainamide. Imipramide (1 and 5 mg/kg-1) or procainamide (5 and 10 mg/kg-1) or solvent were injected intravenously 30 min before ligation. Imipramine reduced the total number of ventricular ectopic beats as well as the incidence and duration of ventricular tachycardia and ventricular fibrillation. The drug did not significantly affect the blood pressure but reduced the heart rate. The antiarrhythmic activity of imipramine is postulated to be due to a quinidine-like effect and/or alpha-adrenergic blocking activity. The study confirms the potential utility of imipramine as an antiarrhythmic drug.

Acceleration of rat brain beta-adrenoceptor subsensitivity following the coadministration of histamine receptor antagonists with imipramine.

Systemic administration of isoprenaline to rats produced a dose-dependent increase in water drinking which was effectively blocked by propranolol. This dipsogenic effect was significantly inhibited by the subacute (4 days) administration of imipramine (18.1 mg/kg/day) together with either the H1-histamine receptor antagonist, chlorpheniramine (0.1 or 1.32 mg/kg/day), or the H2-histamine antagonist, cimetidine (1.91 mg/kg/day) or ranitidine (0.60 or 1.51 mg/kg/day). The oral subacute administration of imipramine alone had no significant effect on this behavior. However, chronic ingestion of imipramine alone (21 days) caused a significant reduction in the isoprenaline-induced behavior. It is concluded that the desensitization of central beta-adrenoceptors, as evidenced by inhibition of isoprenaline-induced drinking, can be accelerated following the oral subacute co-administration of imipramine with either H1- or H2-histamine receptor antagonists. It is also seems the central histamine receptors may partially contribute towards the mechanism of antidepressant effect of imipramine.

Study on the renal and cardiovascular activities of aminouracil derivatives.

The synthesis of five 4-aminouracil derivatives has been described. These compounds, which are chemically related to xanthines, were tested for possible diuretic activity. The increase in urine output by compounds I, III, and V was comparable to that produced by caffeine in an equimolar dose (5 x 10(-3) M). On the isolated rabbit's heart (Langendorff's preparation), compounds I, III, and V (5 x 10(-5) M) significantly increased the amplitude of contractions without having any significant effect on heart rate. Only these three compounds (4.4 x 10(-8) M) relaxed the isolated rabbit thoracic aorta and rat anococcygeus smooth muscle which were precontracted with norepinephrine (4 x 10(-8) M). This action was not antagonized by atropine, propranolol, or methylene blue, ruling out the involvement of acetylcholine, beta receptors, or endothelium-derived relaxing factor (EDRF). The relaxant effect, however, was reversed by the addition of calcium chloride, suggesting that this relaxation may be due to inhibition of the entry of extracellular calcium into the cells.

Antipsychotic properties of new N-(4-substituted-1-piperazinylethyl)- and N-(4-substituted-1-piperidinylethyl)-phthalimides.

A series of N-(4-phenyl- and 4-pyridyl-1-piperazinylethyl)- and N-(4-phenyl-1-piperidinylethyl)-phthalmides were synthesized and tested for antipsychotic activity. All compounds suppressed the spontaneous motor activity and the apomorphine-induced climbing in mice and pergolide-induced locomotor activity in rats, demonstrating psychotropic properties equal to the corresponding properties of sulpiride. Although the compounds, like sulpiride, were less potent than haloperidol in blocking the locomotor activities, they caused no catalepsy, a major side effect following treatment with conventional antipsychotic agents. It is likely that the new compounds produce their neuroleptic activities through inhibition of limbic dopamine receptors.

Interaction of some atypical antidepressants and adrenoceptor antagonists with imipramine: a behavioural study with isoprenaline-induced drinking.

The systemic administration of isoprenaline to rats produced a dose-dependent increase in drinking which was antagonized by propranolol. While oral administration of the antidepressant, imipramine, alone had no significant effect on this response, the increase was significantly inhibited by administration of imipramine together with each of the following drugs over a period of 4 days: bupropion (21.0 mg/kg/day, p.o.), a selective inhibitor of the uptake of dopamine and nomifensine (10.6 mg/kg/day, p.o.), a relatively selective dopamine and a blocker of the uptake of noradrenaline. Similarly, the combination of the selective alpha 1-adrenoceptor antagonist, prazosin (2.37 mg/kg/day, p.o.); the selective alpha 2-adrenoceptor antagonist, yohimbine (2.38 mg/kg/day, p.o.) or the non-selective alpha-adrenoceptor blocker, phentolamine (4.65 mg/kg/day, p.o.) with imipramine caused a significant inhibition of the isoprenaline-induced drinking. It is concluded that fast desensitization of central beta-adrenoceptors in the rat can be produced after the oral subacute simultaneous administration of imipramine with alpha-adrenoceptor antagonists or atypical antidepressants, such as nomifensine or bupropion.

Desensitization of beta-adrenoceptors following repeated injections of 2-substituted 4-phenylquinolines.

The chronic effects of five 2-substituted 4-phenylquinoline derivatives on the sensitivity of the noradrenergic cyclic AMP-generating system in the rat brain cortex have been determined, and compared with those of the typical and atypical antidepressants imipramine and trazodone, respectively. Acute treatment (single i.p. dose of 20 mg kg-1) and sub-chronic treatment (20 mg kg-1 daily for 10 days) induced no significant desensitization of the beta-adrenoceptors. However, chronic treatment (20 mg kg-1 daily for 3 weeks) significantly decreased the isoprenaline-induced increase in cyclic AMP, suggesting desensitization. This effect, coupled with previous findings, points to a potential role of these compounds as antidepressants.