Sympathetic nervous system response in acute cardiovascular toxicity induced by amitriptyline in conscious rabbits

Plasma versus bone marrow desipramine: a comparative study

Correlation between plasma and bone marrow tricyclic antidepressants has not been studied before. Two groups of rabbits were given 10 and 20 mg of desipramine/kg body weight, respectively. Desipramine was administered to the animals once daily by mouth for 5 days. On the fifth day the animals were sacrificed and blood and bone marrow samples were collected and analyzed using a high performance liquid chromatographic (HPLC) method. Data showed that a correlation exists between bone marrow and blood desipramine. The bone marrow desipramine concentration increased as its blood levels increased. The average ratio of bone marrow to blood desipramine +/- S.D. (standard deviation) in both dosage groups was 37.2 +/- 4.46 with a range of 30.99-44.82. This investigation is promising and shows that bone marrow could be used as an alternative tissue in the absence of a suitable blood sample.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants: II

This survey continues a second series of compilations of data regarding changes in body temperature induced by drugs and related agents. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on the presence of special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent. Most of the papers were published from 1980 to 1984 but data from many earlier papers are also tabulated.

Tricyclic antidepressant poisoning. Management of arrhythmias

Deaths from tricyclic antidepressant (TCA) overdose are usually due to arrhythmias and/or hypotension. Tricyclic antidepressant toxicity is due mainly to the quinidine-like actions of these drugs on cardiac tissues. Slowing of phase 0 depolarisation of the action potential results in slowing of conduction through the His-Purkinje system and myocardium. Slowed impulse conduction is responsible for QRS prolongation and atrioventricular block, and contributes to ventricular arrhythmias and hypotension. Therapies that improve conduction, e.g. hypertonic sodium bicarbonate, are useful in treating these toxic effects. Other mechanisms contributing to arrhythmias include abnormal repolarisation, impaired automaticity, cholinergic blockade and inhibition of neuronal catecholamine uptake. Toxicity may be worsened by acidaemia, hypotension or hyperthermia. Sinus tachycardia is due to the anticholinergic effects of the tricyclic antidepressants as well as blockade of neuronal catecholamine reuptake. Sinus tachycardia is generally well-tolerated and requires no therapy. Sinus tachycardia with QRS prolongation may be difficult to distinguish from ventricular tachycardia. Electrocardiograms obtained using oesophageal or atrial electrodes may be useful in determining the relationship of atrial and ventricular activity. Although QRS prolongation alone is not compromising, it is a marker for patients at highest risk of developing seizures, arrhythmias or hypotension. Ventricular tachycardia (monomorphic) is a consequence of impaired myocardial depolarisation and impulse conduction. Hypertonic sodium bicarbonate may partially correct impaired conduction and be of benefit in treating ventricular tachycardia. Since hypertonic sodium bicarbonate appears to act by increasing the extracellular sodium concentration as well as by increasing extracellular pH, hyperventilation may be less effective. Hypertonic sodium bicarbonate is of particular benefit in patients who are acidotic, since acidosis aggravates cardiac toxicity. However, administration of hypertonic sodium bicarbonate is beneficial even when blood pH is normal. Lignocaine (lidocaine) may be useful in treating ventricular tachycardia but should be administered cautiously to avoid precipitating seizures. Ventricular bradyarrhythmias are due to impaired automaticity or depressed atrioventricular conduction and can be treated by placement of a temporary pacemaker, or with a chronotropic agent, e.g. isoprenaline (isoproterenol), with or without concomitant vasoconstrictors.(ABSTRACT TRUNCATED AT 400 WORDS)

Relative acute cardiovascular toxicity induced by maprotiline, mianserin and nomifensine in conscious rabbits

The relative acute cardiovascular toxicity among three novel antidepressants: maprotiline, mianserin and nomifensine, has been assessed in conscious rabbits ip injected at 50 mg/kg, throughout a 150 min observation period. No death was observed in mianserin rabbits (n = 6), but 3 in the maprotiline rabbits (n = 8) and 1 death in the nomifensine group (n = 8), within the 2 hours. Cardiac output and renal blood flow were determined by the radioactive Sephadex microspheres method. Cardiac output values were significantly lowered (-29%) at 120 min only in mianserin rabbits, whereas renal blood flow values were reduced by 46.8% (mianserin, 35.8% (maprotiline) and 28% (nomifensine) at 120 min. In mianserin and maprotiline rabbits left ventricular pressure and mean arterial pressure fell significantly, but remained unchanged in nomifensine group. ECG disturbances consisting of ventricular and supraventricular extrasystoles were seen in all the injected rabbits, but QRS widening and right bundle branch block were solely observed after maprotiline and mianserin. Nomifensine rabbits experienced severe seizures with hypocapnia and metabolic acidosis. The drug myocardial/plasma ratio ranged between 59.3 (maprotiline) 13.25 (mianserin) and 0.92 (nomifensine). A rise in plasma catecholamines (epinephrine) was documented after mianserin but not after nomifensin and maprotiline. Nomifensine exhibited much lesser cardiotoxicity than mianserin and maprotiline at this dose (50 mg/kg), but induced more convulsions.

Protective effects of clonidine and verapamil in experimental amitriptyline poisoning in rabbits

The effects of various agents on acute amitriptyline-induced cardiotoxicity were investigated in conscious rabbits. Amitriptyline (50 mg/kg, IP) regularly produced consistent and reproducible electrocardiographic changes such as lengthening of Q-T intervals, widening of the QRS complex, arrhythmias of various types, convulsion, and severe hypotension. Prevention of these toxic manifestations by the use of various agents alone or in combination was explored. Clonidine (50 micrograms/kg, IV) and verapamil (0.25 mg/kg, IV) alone or in combination at lower doses (25 micrograms/kg plus 0.125 mg/kg, respectively) significantly reduced the lengthening of the QRS and Q-T intervals, restored sinus rhythm, maintained blood pressure at a constant level, and protected against a lethal dose of amitriptyline (75 mg/kg). These results suggest that verapamil, clonidine, and their combination appear to be promising antidotal agents in restoring cardiac function under these conditions.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants

This survey, the third in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of adrenergic and serotonergic agonists and their antagonists including ergot alkaloids, amphetamines, tryptamines, monoamine oxidase inhibitors, tricyclic and other antidepressants, a variety of other agents which alter presynaptic aminergic mechanisms including reserpine, 6-hydroxydopamine, p-chlorophenylalanine, alpha-methyltyrosines, cocaine, guanethidine and bretylium. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.