Responses of contractile function to ruthenium red in rat heart

Isolated rat hearts exhibited a biphasic contractile response to varying concentrations of ruthenium red. A negative inotropic effect was observed with concentrations of 0.025-0.5 microM, whereas a reversal of these initial changes toward control or even exceeding the predrug values was obtained as ruthenium red concentration was increased to 2.5 or 5.0 microM. High concentrations (12.5-25.0 microM) of ruthenium red caused a sustained contracture. In contrast, isolated frog hearts exhibited only a sustained negative inotropic effect at 0.25-12.5 microM ruthenium red. In studies with rat heart, both negative and positive inotropic effects of 2.5 microM ruthenium red were blocked either by increasing the concentration of Ca2+ (from 1.25 to 5.0 mM) or by decreasing the concentration of Na+ (from 140 to 35 mM) in the perfusion medium. The contracture induced by 12.5 microM ruthenium red was markedly inhibited when Ca2+ in the medium was lowered. The positive inotropic effect and contracture due to ruthenium red were also blocked by 1 microM of verapamil and 1.5 mM of amiloride; however, these interventions did not prevent the initial negative inotropic effect of ruthenium red. These experiments suggest the role of extracellular Ca2+ in the dose- and time-dependent effects of ruthenium red on contractile function of the rat heart. Furthermore, the positive inotropic response to ruthenium red may be related to its actions on the Na+-dependent Ca2+ movements in the cardiac cell.

Defects in sarcolemmal Ca2+ transport in hearts due to induction of calcium paradox

Na+-Ca2+ exchange and Ca2+-pump activities were studied in sarcolemmal vesicles isolated from rat hearts subjected to "calcium paradox" on perfusion with Ca2+-free medium followed by reperfusion with medium containing 1.25 mM Ca2+. Perfusion of hearts with Ca2+-free medium for 5 minutes did not affect the Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake, or Ca2+-stimulated ATPase activities in sarcolemma. Reperfusion of the Ca2+-deprived hearts with medium containing Ca2+ for 1-2 minutes increased Na+-dependent Ca2+ uptake, whereas reperfusion for 5-10 minutes decreased Na+-dependent Ca2+ uptake in sarcolemmal vesicles. Both ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities in sarcolemma were depressed on reperfusion of Ca2+-deprived hearts for 2-10 minutes. Reperfusion of Ca2+-deprived hearts for 5 minutes, which failed to generate contractile force, resulted in contracture without any recovery of the contractile force development. These changes in sarcolemmal Ca2+ transport and contractile function were prevented when hearts were perfused with Ca2+-free medium either in the presence of low sodium (35 mM) or at a low temperature (21 degrees C) before starting the reperfusion. No alterations in the purity of the preparation or permeability of sarcolemmal vesicles with respect to Na+ or Ca2+ were detected in hearts perfused with Ca2+-free medium or on reperfusion with medium containing calcium. The results indicate abnormalities in sarcolemmal Na+-Ca2+ exchange and Ca2+-pump mechanisms on reperfusion of Ca2+-deprived hearts with medium containing Ca2+, and such changes may partly account for the occurrence of intracellular Ca2+ overload during the development of calcium paradox.

Effect of cigarette smoke inhalation on antioxidant enzymes and lipid peroxidation in the rat

Inhalation of cigarette smoke significantly increased glutathione (GSH) content and increased lipid peroxidation without altering the activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-Px) or glutathione reductase (GR) in the lung (six male Wistar rats). Following intratracheal administration of benzo[a]pyrene (BP), an increase in pulmonary GSH-Px activity, GSH content and lipid peroxidation was observed after 12 h. GSH-Px activity and GSH content returned to control values by 7 and 30 days, respectively, whereas lipid peroxidation in the lung remained significantly greater than the control value for up to 7 days of BP administration. Hepatic activity of SOD was increased significantly, whereas the activities of GSH-Px, catalase, GR, and GSH content were not changed by inhalation of cigarette smoke. On administration of BP, a significant increase in the activities of SOD and GSH-Px was observed at 12 h. After 7 and 30 days, the activities of these antioxidant enzymes were comparable to their respective control group values. No change in the activity of catalase or in the level of lipid peroxidation was noted throughout the entire study period.

Phospholipid N-methylation-dependent alterations of cardiac contractile function by L-methionine

Isolated rat, rabbit and guinea pig hearts exhibited an initial negative inotropic (20-30%) effect followed by a positive inotropic response (60-80%) upon perfusion with 300 microM L-methionine. In contrast, frog hearts did not show any delayed positive inotropic effect, whereas initial negative inotropic effect (25%) of L-methionine was seen. In subsequent studies using rat hearts, methionine was found to induce a dose-dependent increase in contractile force which correlated linearly (r = 0.93) with incorporation of methyl groups into tissue N-methylated phospholipids. The presence of adenosine, L-homocysteine thiolactone and erythro-9-(2-hydroxy-3-nonyl) adenine mixture in the perfusion medium inhibited the contractile effects of L-methionine as well as the incorporation of 3H-methyl groups by about 75%. Cycloleucine, an inhibitor of S-adenosylmethionine synthase, and methyl acetimidate, a blocker of the phosphatidylethanolamine polar groups, inhibited phospholipid N-methylation and prevented the contractile changes due to L-methionine. The initial negative inotropic effect of methionine was attenuated by lowering the concentration of Na+, whereas the delayed positive inotropic effect was dependent on the concentration of Ca++ in the perfusion medium. Ryanodine, a blocker of the sarcoplasmic reticular Ca++ release, prevented the positive inotropic effect of methionine whereas verapamil, a well known Ca++ antagonist, blocked the initial depressant effect and reduced the delayed positive inotropic response. Marked alterations in the sarcolemmal and sarcoplasmic reticular calcium transport activities were seen upon perfusing the hearts with methionine.(ABSTRACT TRUNCATED AT 250 WORDS)

Methionine-induced positive inotropic effect in rat heart: possible role of phospholipid N-methylation

Perfusion of isolated rat heart with L-methionine produced a positive inotropic effect that was temporally preceded, as well as accompanied, by an increase of methyl group incorporation into N-methylated phospholipids of the myocardium. Maximal increase in contractile force development was associated with maximal methyl group incorporation. Both parameters showed a dose-related dependence on methionine and correlated positively (r = 0.965) upon regression analysis of the data. The presence of adenosine, L-homocysteine thiolactone and erythro-9-(2-hydroxy-3-nonyl) adenine in the perfusion medium inhibited the positive inotropic effect as well as the incorporation of methyl groups into phospholipids. Cycloleucine, an inhibitor of S-adenosylmethionine synthetase, also reduced the increase in contractility by methionine. Methionine-induced positive inotropic effect could be modulated by varying Ca2+ concentration in the perfusate and was inhibited by ryanodine, a blocker of sarcoplasmic reticular Ca2+ release. These observations indicate that L-methionine may serve as a powerful positive inotropic agent and suggest that phospholipid N-methylation plays an important role in functional activity of rat heart.

Characterization of insulin receptors in cardiac sarcolemmal and sarcoplasmic reticular membranes

Specific insulin binding sites in cardiac sarcolemmal (SL) and sarcoplasmic reticular (SR) membranes were examined. Under in vitro conditions, the specific insulin binding to SL was two to three times greater than that to SR isolated from myocardium of different species. Insulin binding to these membranes was rapid, saturable, and temperature dependent. Scatchard plots were nonlinear and revealed high-affinity sites with K1 of 1.2 +/- 0.1 and 2.3 +/- 0.4 nM and low-affinity sites with K2 of 34.0 +/- 11.6 and 87.7 +/- 18.7 nM for SR and SL membranes, respectively. Unlabeled insulin accelerated the dissociation of previously bound labeled insulin, reflecting negative cooperativity of site-to-site interaction in both membranes; however, the dissociation rate in SR was about twofold higher than that in SL. The optimum binding of insulin to SR showed a plateau between pH 6.5 and 7.5 in comparison with a sharp peak at pH 8.0 for SL. Insulin significantly enhanced ATP-dependent Ca2+ binding to SL and SR membranes by approximately 100 and 40%, respectively. The Na+-dependent Ca2+ uptake in SL and the oxalate-supported Ca2+ uptake in SR were also stimulated by insulin; the maximum increase in Ca2+ accumulation in these vesicles was approximately 150 and 25%, respectively. These studies indicate that specific insulin binding sites in SL are characteristically distinct from those in SR and that insulin is capable of stimulating Ca2+ pumps located in these membranes.

Effect of excessive intake of ascorbic acid on hepatic and extra-hepatic phase I and phase II drug metabolism in rat

Guinea pig is the animal model of choice for studies on effects of ascorbic acid (AA). However, rat is one of the largely used animals for investigations related to chemical carcinogenesis. Therefore, the present study was designed to evaluate the changes induced by high intake of the vitamin in xenobiotic and carcinogen metabolizing status of the organs. Male Wistar rats, dosed daily with 50 mg AA/100 g body weight for 10 weeks, demonstrated a small non-significant increase in hepatic, pulmonary and colon cytochrome P-450 (Cyt. P-450) contents, which was accompanied with a significant increase in hepatic and pulmonary arylhydrocarbon hydroxylase (AHH) activities. Phase II enzymes of drug metabolism responded in different ways to increased intake of AA. UDP-glucuronyltransferase (UDPGT) activity was unaffected in liver and colon, but it was increased (p less than 0.005) in lung. Activities of glutathione S-transferase (GST) were decreased in the three organs. Inducibility of AHH by 3-methylcholanthrene (MCA) or phenobarbital (PB) was largely reduced due to AA feeding. Besides this, MCA and PB had differential effects on enzymatic levels in AA fed rats. When compared with our earlier observations in guinea pig, it was found that rat responded similarly to guinea pig to increased intake of AA with regard to hepatic AHH, Cyt. P-450, UDPGT and GST, pulmonary AHH, Cyt. P-450 and Cyt. b5, and all studied colon enzymes, except GST.

Calcium pump activity of sarcoplasmic reticulum in diabetic rat skeletal muscle

Ca2+ pump activity of skeletal muscle microsomes containing fragments of sarcoplasmic reticulum was examined in rats 8 wk after the induction of chronic diabetes by an intravenous injection of streptozotocin (65 mg/kg). In comparison with the control values, both ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities were increased in the microsomal fraction from diabetic rats. These changes were seen as early as 7 days after streptozotocin injection and were apparent at various times of incubation (1-10 min) as well as at different concentrations of free Ca2+ (10(-7)-5 X 10(-5) M Ca2+). Insulin administration to diabetic animals for 2 wk reversed Ca2+ uptake and ATPase activities to control levels. The increase in microsomal ATPase activity of the diabetic preparation due to cAMP-dependent protein kinase or calmodulin was greater than in the control microsomes and the depression by a specific inhibitor of protein kinase, but not of calmodulin, was greater in diabetic muscle. The enhanced Ca2+ pump activity was associated with altered phospholipid composition and protein profile of the diabetic preparations. The rate of Ca2+ release from microsomal vesicles was unaffected by the diabetic condition. Isometric contractile force development as well as positive dF/dt and negative dF/dt of the skeletal muscle from diabetic animals were higher at different pulse strengths (0.5-100 V) and at different Ca2+ concentrations (0.25-2.5 mM). These results suggest that diabetes is associated with enhanced sarcoplasmic reticular Ca2+ pump activity, and this may account for the hyperfunction of skeletal muscle in this disease.

[Cardiotonically Active Principles from Spigelia anthelmia1.]

From the upper parts of SPIGELIA ANTHELMIA L. besides some widely distributed phenolcarboxylic acids and flavonoids two volatile alkaloids have been isolated and identified as isoquinoline and an iridoid compound of the actinidine type. In the water extract choline, benzoylcholine and 3,3-dimethyl-acryloylcholine could be identified. Preliminary pharmacological investigations revealed that the alkaloids are involved in the cardiotonic activity of the plant.

Effect of large doses of ascorbic acid on the hepatic and extra-hepatic drug-metabolizing enzymes in guinea pig

Water solubility and non-toxic properties of ascorbic acid are taken as criteria for beneficial effects of large doses of the vitamin. In the present study, male guinea pigs, dosed daily with 15, 30 or 50 mg/100g body weight for 10 weeks, demonstrated no differences in effect on liver and lung weights, body growth and microsomal protein contents of liver and lung when compared with controls. When guinea pigs were fed excessive ascorbic acid, there was a small non-significant increase (p less than 0.05) in hepatic and pulmonary cytochrome P-450, and significant increase (p less than 0.05) in hepatic cytochrome b5 which was accompanied with a significant increase in arylhydrocarbon hydroxylase activity in the two organs. Activity of NADPH-dependent cytochrome c-reductase was decreased in liver and remained unaffected in lung and colon. Drug detoxifying enzymes responded in different ways to increased intake of ascorbic acid. Activity of UDP-glucuronyltransferase remained unchanged on feeding excessive ascorbic acid, whereas glutathione S-transferase was decreased significantly in liver and was unaltered in lung and colon. Reduced glutathione was decreased only in the lung. The observed changes in drug activating and detoxifying enzymes appear to be important from drug pharmacokinetics and carcinogenesis point of view.

Stimulation of Na+-Ca2+ exchange in heart sarcolemma by insulin

Insulin was found to stimulate Na+-dependent Ca2+ uptake in dog heart sarcolemma in a concentration dependent manner (0.001 to 1 milliunits/ml). Maximal stimulation (160 to 170%) was seen at 0.1 to 1 milliunits/ml of insulin. Unlike Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake was unaltered by 1 microunit/ml of insulin. However, high concentrations of insulin (0.01 to 1 milliunits/ml) significantly increased the ATP-dependent Ca2+ uptake activity of heart sarcolemma; maximal increase (60%) was observed at 1 milliunit/ml of insulin. The Na+ K+-ATPase activity did not change upon incubating sarcolemma with insulin. The membrane preparation exhibited specific insulin binding characteristics. The Scatchard plot analysis of the data indicated two binding sites for insulin; the association constants for the high and low affinity sites were 2 X 10(9) M-1 and 4.4 X 10(8) M-1, respectively. These results support the view regarding the presence of insulin receptors in the heart cell membrane and indicate a dramatic effect of insulin on the sarcolemmal Ca2+ transport systems.

Differential effects of autonomic blockade on sinus and atrioventricular nodal function in normals and in intrinsic sinus node dysfunction

The effect of pharmacologic total autonomic blockade on sinus and atrioventricular nodes was studied in 10 normals and 21 patients with sick sinus syndrome with abnormal intrinsic corrected sinus node recovery time. In normals the intrinsic heart rate (113.3 +/- 11.6 beats/min) was higher than the resting heart rate (87.3 +/- 12 beats/min; P less than 0.001). The AH interval at an identical paced rate decreased from 119 +/- 36 msec to 93 +/- 17.6 msec after autonomic blockade (P less than 0.05). Mean atrial paced cycle length at AH Wenckebach block was not different during control and after drugs (319 +/- 46 msec vs. 311.5 +/- 39 msec; P = NS). Although sinus cycle length shortened in all cases after autonomic blockade, paced cycle length at AH Wenckebach increased (4) or remained unchanged (3) in 7 cases. Maximum normal "intrinsic" paced cycle length at AH Wenckebach was 390 msec (mean +/- 2 SD). In sick sinus syndrome, resting heart rate (66.3 +/- 18.8 beats/min) and intrinsic heart rate (74.6 +/- 16.4 beats/min) were similar (P = NS); AH at identical paced rate: control 136.6 +/- 54 msec, after drugs 130.5 +/- 35 msec (P = NS); cycle length at AH Wenckebach: control 380.5 +/- 73 msec, after autonomic blockade 383 +/- 49 msec (P = NS). Two of 3 cases with abnormal atrioventricular nodal response to atrial pacing during control normalized after autonomic blockade; 9/21 (42.8%) cases developed AH Wenckebach at cycle length greater than 390 msec after autonomic blockade. The data suggest that the autonomic nervous system has differential effects on sinus and atrioventricular nodes. Patients with sick sinus syndrome frequently have abnormalities of "intrinsic" atrioventricular nodal conduction unmasked by autonomic blockade.

Verapamil in idiopathic ventricular tachycardia of right bundle branch block morphology: observations during electrophysiologic and exercise testing

Electrophysiologic studies before and after administration of verapamil were performed in three young patients with recurrent sustained ventricular tachycardia (VT) of right bundle branch block morphology. VT was not provoked by maximal treadmill testing in any patient. Electrophysiologic findings at induction of VT suggested reentry in the first patient and triggered automaticity in the second. Findings were inconclusive in the third patient. Intravenous verapamil terminated the VT in all the three cases. Oral verapamil prevented laboratory induction of sustained VT in the latter two patients. However, VT could be provoked during exercise in both while on oral verapamil therapy. These findings suggest that different mechanisms may underlie ventricular tachycardia dependent upon slow-response tissue; the role of oral verapamil in the treatment of such VT needs further investigation.

The effect of vitamin A deficiency on the initiation and postinitiation phases of benzo(a)pyrene-induced lung tumourigenesis in rats

The present investigation shows the effect of vitamin A deficiency on the initiation and postinitiation phases of benzo(a)pyrene-induced lung carcinogenesis in male Wistar rats. Lung tumours were induced by giving three intratracheal instillations, one week apart, of 10 mg benzo(a)pyrene per instillation. Maximum tumour incidence (100%) and tumour burden per rat was found in rats which were kept on vitamin A deficient diet for 4 weeks prior to the first administration and 8 weeks after the last administration of benzo(a)pyrene. Rats in which vitamin A deficiency was terminated after the last administration of the carcinogen had 83% tumour incidence, whereas corresponding control pairfed animals had 39% incidence of tumours. These data represent the values obtained 32 weeks after the last administered dose of the carcinogen and indicate the role of vitamin A, both in the initiation as well as in the postinitiation phases of lung carcinogenesis.