Effects of lidocaine on sarcolemmal fluidity and cellular cAMP in rat cardiomyocytes

Antiarrhythmic drugs with local anesthetic properties modify the physical state of membrane phospholipids and could change adenylate cyclase activity and, thus, influence cardiac ischemic arrhythmias. Adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in cardiomyocytes cultured from newborn rat and fluorescence anisotropy of sarcolemma-enriched membranes were investigated in the presence of a neutral anesthetic drug benzyl alcohol and of a cationic anesthetic drug lidocaine. Benzyl alcohol increased in a dose-dependent manner both sarcolemma fluidity and isoproterenol- or cholera toxin-stimulated cAMP accumulation. In contrast, benzyl alcohol inhibited cAMP accumulation in forskolin-stimulated cells. Lidocaine induced a dose-related inhibition of isoproterenol-, forskolin-, and cholera toxin-stimulated cAMP accumulation without eliciting any change in sarcolemma fluidity. The inhibitory effect of lidocaine on isoproterenol-stimulated cAMP accumulation was reversed when cells were pretreated with pertussis toxin. These data suggest that the inhibitory effect of lidocaine on cAMP synthesis might involve a polar interaction with the Gi regulatory subunit of adenylate cyclase. Such an effect could contribute, in vivo, to both the antiarrhythmic and the negative inotropic effect of lidocaine.

Adaptation to Pi deprivation of cell Na-dependent Pi uptake: a widespread process

Phosphate enters kidney proximal tubular cells through an apical sodium-phosphate cotransport; this activity (Vmax) increases during phosphate deprivation (Kidney Int. 18: 36-47, 1980). This study investigated the mechanism of phosphate uptake and its adaptation to phosphate deprivation in cultured cells from different origins (kidney, LLC-PK1 and MDCK cells; liver, Fao cells; heart, myocyte primary cultures). All cells exhibited a sodium-dependent phosphate uptake that was reduced (greater than 75%) by external sodium substitution and inhibited by ouabain (35%) and 2,4-dinitrophenol or KCN (80%). Phosphate deprivation (exposure to phosphate-free medium) increased sodium-dependent phosphate uptake by 1.8- to 5.8-fold and decreased cell inorganic phosphate and ATP contents (70-80 and 17-30%, respectively). The stimulation of phosphate uptake resulted from an increase in Vmax without change in Km and was dependent on gene transcription and protein synthesis because it was inhibited by cycloheximide and 3-deoxyadenosine. Thus a deprivation-stimulated, sodium-dependent phosphate transport was demonstrated in cells originating from distal kidney tubules, liver, and heart. The findings suggest that in hypophosphatemic diseases, impairment of renal proximal phosphate reabsorption might be only one expression of a widespread alteration of cell phosphate regulation.

Amiodarone pharmacokinetics in coronary patients: differences between acute and one-month chronic dosing

The pharmacokinetics of amiodarone (A) and its desethylamiodarone metabolite (DEA) were compared in the same coronary patients after a first 1000 mg dose and one-month chronic oral dosing. Terminal half-life (t1/2 el) of amiodarone increased from a mean (SD) 24.1 +/- 19.5 h after the first dose to 20.4 +/- 4.8 days after the last dose. Desethylamiodarone slowly appeared in the plasma after the first oral dose and its apparent t el was 61.6 +/- 26.6 h. After one-month dosing apparent t1/2 el of desethylamiodarone increased to 29.5 +/- 9.7 days. Mean maximal plasma amiodarone/desethylamiodarone concentration ratio decreased from 9.2 +/- 5.0 to 2.0 +/- 0.6 after chronic dosing. This change was mainly related to an increase in the plasma concentration of desethylamiodarone. These data suggest that after long-term treatment with amiodarone, the complete elimination of the drug and its metabolite may need 3-4 months in some patients. The results of this study were presented in part at the meeting of the Societe Francaise de Therapeutique et de Pharmacologie Clinique, Paris, December 1985.

Prostaglandin synthesis and membrane fatty acid composition in the heart of obese Zucker rats

Genetically obese Zucker rats share several abnormalities with obese patients: inheritance of the obesity, hyperinsulinemia, hypertriglyceridemia. Because alterations in membrane fatty acid composition and in prostaglandin synthesis can be involved in the genesis of the cardiovascular complications of obesity, cardiac prostaglandins and phospholipid fatty acid composition were compared in obese and lean animals. Obese cardiac tissues produced smaller amounts of prostacyclin, thromboxane A2 and PGE2 than lean (p less than 0.01). The cyclooxygenase pathway and the activation of phospholipase by the calcium ionophore A 23187 were not altered. Phospholipid fatty acid composition of obese tissues was abnormal: the amount of stearic, arachidonic, docosapentaenoic and cervonic acids was decreased, whereas the amount of linoleic acid, the precursor of arachidonic acid, was doubled. It is concluded that obesity in Zucker rats is associated with alteration of cardiac arachidonic acid metabolism and that the alterations associated with obesity can be studied in this rat strain.

Strial prostaglandins and leukotrienes. Biochemical characteristics and interrelationship with furosemide

Synthesis of prostaglandins (PGs) was characterized in the lateral wall (LW) of guinea-pig cochlea. Basal synthesis at 37 degrees C was about 480 pg/LW (12.8 ng X mg-1 protein) for PGI2 and 85 pg/LW (2.3 ng X mg-1 protein) for PGE2, levelling out after 10 min of incubation. Incubation with arachidonic acid (10(-5) M) increased PGI2 and PGE2 synthesis by 44% and 1020%, respectively, showing that arachidonic acid availability is a synthesis-limiting factor. The stimulating effect of the Ca++ ionophore A23187 (5 X 10(-6) M) on PG synthesis was weak (about +50%) but was enhanced (about +140%) by preincubation with arachidonic acid. Angiotensin II (10(-6) M), vasopressin (5 X 10(-7) M), and furosemide (10(-8) to 10(-3) M) did not alter PG secretion. Neither aspirin nor indomethacin prevented the development of furosemide ototoxicity (endocochlear potential) in the rat. Perfusion with PGI2 influenced the furosemide effect in some instances.

Prostaglandins in the semicircular canal of the frog

The synthesis of prostaglandins by ampulla and duct tissue isolated from the frog posterior semicircular canal was investigated in vitro. Ampulla and duct produced PGE2 (9 and 6 pg/structure, respectively) and prostacyclin (26 and 12 pg/structure). In the ampulla, prostaglandins mostly originated from the part containing dark and sensory cells and was not altered by 10(-3) M streptomycin. Prostaglandin levels were time-dependent and temperature-dependent. Arachidonic acid (3 X 10(-5) M) stimulated PGI2 synthesis by ampulla and duct (by 11.4 and 17 times) and PGE2 synthesis by 50 times in both structures. Ionophore A23187 stimulated ampulla and duct PGI2 synthesis (by 4.8 and 5.6 times) and PGE2 synthesis (by 2.4 and 1.8 times). Subcutaneous 100 mg/kg aspirin reduced PGI2 and PGE2 synthesis (ampulla: -87%, -33%; duct: -100%, -33%). Indomethacin (10(-6) M), in vitro, decreased PGI2 and PGE2 synthesis (ampulla: -47%, -47%; duct; -22%, -77%). Within 3 h, aspirin (5 X 10(-6) M) or arachidonic acid (2 X 10(-5) M) did not change Na and K concentrations in endolymph. It is concluded that frog inner ear produces PGI2 and PGE2, mostly from the part containing the dark cells, and that prostaglandins could be involved in the physiology of inner ear.

Calcium antagonists stimulate prostaglandin synthesis by cultured rat cardiac myocytes and prevent the effects of hypoxia

The effect of three calcium antagonists on the synthesis of prostacyclin (PGI2, assayed as 6-Keto-PGF1 alpha) and PGE2 by cultured rat cardiac myocytes and fibroblasts was investigated. In myocytes only, bepridil, diltiazem and verapamil (10(-9) to 10(-7) M) stimulated PGs synthesis by two- to three-fold, dose-dependently. At a concentration of 10(-6) or 10(-5) M the intensity of the stimulation of PGI2 and PGE2 decreased. Cobalt chloride (2 X 10(-3) M) did not change PGs synthesis (pg/mg of protein/30 min; means +/- SE, N = 10; PGE2: 365 +/- 59 and 463 +/- 89 treated vs controls; PGI2: 824 +/- 214 and 799 +/- 143 treated vs controls). After 30 min exposure of myocytes to hypoxic conditions (glucose-free medium and low PO2), the glycogen content was half that of the controls (P less than 0.001), ATP content did not change and PGI2 and PGE2 synthesis increased (X1.5, P less than 0.05). When applied to myocytes 30 min before inducing hypoxia, the three calcium antagonists stimulated PGs synthesis by three- to seven-fold at maximal effect, and bepridil (10(-8) M) or diltiazem (10(-7) M) prevented the hypoxia-induced decrease in glycogen content. With 10(-5) M drug concentration, the effect on PGs was not significant, except for the effect of bepridil on PGI2 (P less than 0.05). It is concluded that therapeutic concentrations of calcium antagonists simultaneously prevent the decrease in myocyte glycogen induced by hypoxia and stimulate PGs synthesis by myocytes.

Verapamil depresses the synthesis of lipoxygenase products by hypoxic cardiac rat fibroblasts in culture

Lipoxygenase metabolites of arachidonic acid are potent chemotactic and vasoconstrictive agents and their local production in the myocardium induces the migration of polymorphonuclear cells into ischemic myocardium. These cells have been shown to play a role in the development of ischemic myocardial lesions. In the present study, the synthesis of arachidonic acid lipoxygenase metabolites by rat cardiac cells in culture and the effect of verapamil were investigated under normal and hypoxic conditions. Myocytes and fibroblasts metabolized exogenous arachidonic acid into 12-HETE and an unidentified metabolite (X). Fibroblasts synthesized significantly greater amounts of 12-HETE than myocytes (P less than 0.01). Hypoxia (glucose-free medium and low PO2) and verapamil (10(-7) M) under normal conditions, did not change metabolite synthesis by either type of cells. Under hypoxia, verapamil decreased significantly 12-HETE and X production by fibroblasts (P less than 0.01 and P less than 0.05), whereas the synthesis in myocytes was not changed. It is concluded that the decrease in lipoxygenase product synthesis under hypoxia by verapamil may contribute to its therapeutic effects on the ischemic heart.

Comparison of four beta-blockers as assessed by 24-hour ECG recording

beta-Blockers are used as if they were equivalent. With ECG recordings in 42 patients we investigated the effect on sinus heart rate of four beta-blockers given at three successive daily doses. Heart rate was dose-dependently decreased by all drugs except acebutolol, the effect of which decreased at a higher dosage. The maximal effects of metoprolol, nadolol, and propranolol were similar but the drugs differed in potency (dosage producing 50% of maximal effect, calculated from the dose-effect relationships; nadolol, 0.3 mg/day; metoprolol, 120 mg/day; propranolol, 47 mg/day). Similar relationships were found with drug plasma concentrations (concentration producing 50% of maximal effect: nadolol, 3.5 ng/ml; metoprolol, 21 ng/ml; propranolol, 36 ng/ml) and with supine or upright heart rates and blood pressures. However, the drugs were not equivalent: In addition to its greater potency, nadolol differed from propranolol and metoprolol in the slope of its dose-response curve. We conclude that beta-blockers can be compared by ECG recordings and that nadolol is different from the other beta-blockers without intrinsic sympathomimetic activity.

Amiodarone and N-desethylamiodarone concentrations in plasma, red blood cells, and myocardium after a single oral dose: relation to hemodynamic effects in surgical patients

In an attempt to assess their respective values for purposes of drug monitoring, plasma, red blood cell, atrial, and ventricular concentrations of amiodarone and N-desethylamiodarone (NDA) were measured, in 50 surgical patients, after a single oral dose (30 mg/kg); hemodynamic changes were assessed also. Amiodarone concentration was lower in red blood cells than in plasma and in myocardium. A relationship was found between the red blood cell concentration and plasma or myocardial concentrations of amiodarone (r = 0.79 and r = 0.68, p less than 0.00001). Hemodynamic studies were available in 17 treated patients and 13 control subjects before and at the time of surgery. In control subjects, hemodynamics did not change with time and general anesthesia. Oral amiodarone decreased the cardiac index (p less than 0.05) and heart rate (p less than 0.001) without significant changes in arterial pressure, systemic vascular resistance, or stroke volume index. The increase in capillary wedge pressure was related to amiodarone or NDA plasma, myocardial, and red blood cell concentrations (for amiodarone: r = 0.61, p = 0.006; r = 0.69, p less than 0.001; and r = 0.53, p = 0.02, respectively). We concluded that oral amiodarone impairs hemodynamics and that measurement of the amiodarone plasma concentration rather than the red blood cell concentration is the easiest method of monitoring the drug. However, establishment of the clinical utility of drug monitoring during chronic administration of amiodarone needs further investigation.

[Anti-arrhythmic effect of amiodarone in the 24 hours following a single oral loading dose. Clinical and pharmacological study]

This study demonstrated the rapid antiarrhythmic effects of oral amiodarone (Am). A single 30 mg/kg dose was given to 67 patients, 18 with supraventricular arrhythmias (atrial extrasystoles: 11 cases, reciprocating tachycardia: 4 cases, intraatrial reentrant tachycardia: 2 cases, paroxysmal atrial fibrillation, AF: 1 case). Eighteen patients had permanent AF. Thirty-one patients had ventricular arrhythmias (ventricular extrasystoles, VES, isolated or in salvos: 22 cases, and ventricular tachycardia, VT: 19 cases). The effect on atrial extrasystoles was significant 4 to 13 hours after AM and maximal (-98% +/- 3.6%) at 7.7 +/- 1 hours. They recurred in 3 cases at the 18th hour. No significant effects were observed on the other supraventricular tachycardias. The effect on the atrioventricular node (AVN) assessed by the ventricular response to permanent AF, was significant after the 3rd hour and maximal ( = 38 +/- 6 bpm) at the 7th hour. The reduction in the frequency of VES was significant from the 5th to the 19th hour of treatment. Control of VT was obtained in 5 cases between the 3rd and 8th hours. The treatment was well tolerated as no side effects were reported. The plasma concentration (PC) of amiodarone (54 patients) and of N-desethylamiodarone (NDA) (36 patients) were measured; the maximal values were 2.53 +/- 1.5 mg/l for Am and 0.22 +/- 0.1 mg/l for NDA. A 60% decrease in the number of VES was observed with PC of Am of 1.90 +/- 0.3 mg/l and a 20% reduction in the ventricular response to AF at PC of Am of 1.50 +/- 0.33 mg/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin synthesis by the cochlea of the guinea pig. Influence of aspirin, gentamicin, and acoustic stimulation

This study describes the synthesis of prostaglandins (PGs) by the vascular structures of the inner ear (lateral wall = stria vascularis and spiral ligament) in vitro. The main PGs produced were PGI2, PGF2 alpha and PGE2. PGI2 and PGF2 alpha were also found in the perilymph. A 350 mg/kg ip injection of aspirin decreased PG synthesis by the lateral wall and PG levels in perilymph. This effect was reversed after 3 days. Gentamicin (10(-9) to 10(-5) M) decreased significantly and reversibly PG synthesis in vitro, as did 100 mg/kg ip injection. Acoustic stimulation increased ex vivo PGI2 and PGE2 synthesis without modifying PG levels in perilymph. Results suggest that PGs could be one humoral mediator of the cochlear microcirculation homeostasis, and, possibly, of the circulatory disturbances reported after acoustic stimulation. The decreased PG synthesis after gentamicin treatment could account for the angiotoxic component observed in aminoglycoside ototoxicity.

Suppression of arrhythmias within hours after a single oral dose of amiodarone and relation to plasma and myocardial concentrations

In 65 patients a single oral dose of amiodarone (30 mg/kg) produced an antiarrhythmic effect on supraventricular or ventricular arrhythmias within 3 to 8 hours and lasted for 17 to 19 hours. On the second day a 15-mg/kg dose reproduced this effect within 3 to 9 hours. Plasma concentration of amiodarone increased to a maximum (2.2 +/- 1.7 mg/liter) mean +/- standard deviation) at 6 +/- 3.5 hours and plasma levels of N-desethylamiodarone (NDA) rose to 0.2 +/- 0.08 mg/liter at 12 +/- 6.4 hours. Sixty-one other patients were given a single 30-mg/kg dose 7 hours to 4 days before open heart surgery. Biopsies of the right atrial and left ventricular walls were taken during surgery. Myocardial concentration of amiodarone was maximal in the atrium after 7 hours (13 +/- 8 mg/kg) and in the ventricle after 24 hours (17 +/- 11 mg/kg). NDA myocardial concentration increased progressively until 24 hours and then remained stable over 4 days (1.5 mg/kg). The amiodarone myocardial to plasma concentration ratio was similar in the atrium and in the ventricle and averaged 22 and 10 for amiodarone and NDA, respectively. A significant relation existed between amiodarone concentration and the effect on ventricular premature complexes (r = 0.74, p less than 0.001) and between amiodarone plasma concentration and the effect on the atrioventricular conduction (r = 0.58, p less than 0.001). The plasma concentration of amiodarone corresponding to a 60% decrease in arrhythmias averaged 1.5 to 2 mg/liter.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-blocking therapy in atrial and ventricular tachyarrhythmias: experience with nadolol

The effects of nadolol (N) and propranolol (P) were studied in atrial and ventricular tachyarrhythmias. Interpretation of the results should take into account the dependence of the arrhythmia on the sympathetic tone, and the drug effect on the sinus node frequency. The day/night ratio of the sinus rate is too sensitive a marker of beta blockade to evidence a difference between the two drugs at usual dosages. In contrast, even slight differences (2 to 4 bpm/24 hr) in the absolute value of cardiac frequency may be significant in homogeneous groups of patients treated with high, moderate or low dosages of P or N and, for the latter, on a short- or long-term basis. In 22 of 23 cases of idiopathic adrenergic-dependent atrial tachycardia or fibrillation that were resistant to P (160 mg/day), N (160 mg/day) was effective on a short-term basis, whereas 11 cases of vagally induced atrial flutter-fibrillation were more aggravated by N than by P. However, after 2 weeks to 2 months, 15 of 22 adrenergic-dependent atrial tachyarrhythmias escaped from the initial control, and type I antiarrhythmic agents had to be combined with N. The absence or loss of efficacy of the beta-blocking treatment coincides with the different short-term effects of P and N on the sinus rate and with the different short-term and long-term effects of N. Better efficacy of N over P was also found at the ventricular level when two groups of adrenergic-dependent (nine patients) or nonadrenergic-dependent (10 patients) ventricular tachyarrhythmias of nonischemic origin were compared. At this level, no escape phenomenon was observed. In conclusion, the antiarrhythmic effect of beta blockers essentially depends on the mechanism of the arrhythmia itself. The changes in the sinus rate values reflect the degree of beta blockade, and the antiarrhythmic efficacy depends not only on the dosage but also on the nature of the drug used.

Metabolism of Adenosine Diphosphate by Cultured Umbilical Endothelial Cells

Vascular endothelium has been considered to be responsible for the clearance of circulating adenylnucleotides. Endothelial cells were collected from human umbilical veins and as Pnmary cultures. The cells were incubated in Medium 199 pH 7.4, with 8[14C]-ADP 10-5M and the metabolites were separated by thin-layer chromatography from the supernatant and from the cellular perchloric extract.

ADP was degraded as an exponential function of time into AMP and then into adenosine, which was the main catabolite found in the medium at 30 min. Adenosine was taken up by the cells at a constant low rate and then transformed into ATP. The rate of ADP degradation depended upon the physical state of the cells and was increased by cell dissociation The half life of ADP was S min in presence of adherent cells and 3 min in presence of col 1agenase-dissociated cells. The ADP clearance increased as an exponential function of cell density but decreased with the culture age (5 up to 13 days).

These results suggest that endothelium may control the formation of circulating adenosine, which contributes to local blood flow regulation and to the non-thromboqenic properties of endothelium.