Effects of melittin on adipocyte metabolism unrelated to lysophospholipid accumulation

Melittin addition to rat or hamster adipocytes resulted in inhibition of lipolysis, cyclic AMP accumulation and glucose oxidation. Low concentrations of melittin were not insulin-like with respect to either stimulation of glucose metabolism or inhibition of lipolysis. Higher concentrations of melittin lysed adipocytes. In the presence of melittin, cellular phospholipids were released to the medium and hydrolyzed with little accumulation of lysophospholipids. Only in adipocytes incubated with melittin contaminated with phospholipase A2 was any appreciable accumulation of lysophospholipids seen and this was in the medium. These data suggest that the toxic effects of melittin on adipocytes are not due to the accumulation of lysophospholipids but rather to the loss of membrane phospholipids or alterations in membrane proteins.     

Dose effect of alpha-linolenic acid on lipid metabolism in the hamster

In order to meet dietary requirements, the consumption of alpha-linolenic acid (ALA, 18:3 n-3) must be promoted. However, its effects on triglyceride (TG) and cholesterol metabolism are still controversial, and may be dose-dependent. The effects of increasing dietary ALA intakes (1%, 10%, 20% and 40% of total FA) were investigated in male hamsters. ALA replaced oleic acid while linoleic and saturated FA were kept constant. Triglyceridemia decreased by 45% in response to 10% dietary ALA and was not affected by higher intakes. It was associated with lower hepatic total activities of acetyl-CoA-carboxylase (up to -29%) and malic enzyme (up to -42%), which were negatively correlated to ALA intake (r(2) = 0.33 and r(2) = 0.38, respectively). Adipose tissue lipogenesis was 2-6 fold lower than in the liver and was not affected by dietary treatment. Substitution of 10% ALA for oleic acid increased cholesterolemia by 15% but, as in TG, higher ALA intakes did not amplify the response. The highest ALA intake (40%) dramatically modified the hepatobiliary metabolism of sterols: cholesterol content fell by 45% in the liver and increased by 28% in the faeces. Besides, faecal bile acids decreased by 61%, and contained more hydrophobic and less secondary bile acids. Thus, replacing 10% oleic acid by ALA is sufficient to exert a beneficial hypotriglyceridemic effect, which may be counteracted by the slight increase in cholesterolemia. Higher intakes did not modify these parameters, but a very high dose resulted in adverse effects on sterol metabolism.     

The effect of cigarette smoke on the metabolism of arachidonic acid in isolated hamster lungs

The effects of cigarette smoke on the metabolism of exogenous arachidonic acid (AA) were investigated in isolated hamster lungs. Arachidonate was injected into the pulmonary circulation and the metabolites were analysed from the nonrecirculating perfusion effluent by thin layer chromatography. After the pulmonary injection of 66 nmol of ¹⁴C-AA about 20 % of the injected radioactivity appreated in the perfusion effluent mostly as metabolites in six minutes. When isolated lungs were ventilated with cigarette smoke during the perfusion, the amounts of PGF_2α, PGE₂ and two unidentified metabolite groups increased in the lung effluent. In two other experimental series hamsters were exposed to cigarette smoke before the lung perfusion either once for 30 min or during one hour daily for ten consecutive days. Neither pre-exposures caused any changes in the amounts of arachidonate metabolites in the lung effluent.     

The biological effect of polyamines on heart RNA and histone metabolism

Summary We have observed a close relationship between polyamines (spermine and spermidine) and nucleic acids in connection with myocardial hypertrophy obtained by aortic constriction or by physical exercise. The role of spermine in RNA synthesis has been investigated on perfused heart, and we have observed a rapid increase of ribose-5-³H incorporation into RNA subcellular fractions. With the same experimental conditions we have considered the action of spermine on histone acetylation. The arginine-rich fractions are more acetylated under the action of spermine. This finding indicates a positive action of spermine on gene derepression mechanism.An invited article.     

The effect of lidocaine compared with verapamil on the enhanced ventricular rhythm in the infarcted canine heart

Myocardial ischemia was produced in dogs by the occlusion of the left anterior descending (LAD) coronary artery for 24 or 48 h. After complete atrioventricular block was produced, enhanced ventricular rhythm was observed in all animals. The enhanced ventricular rhythm showed multiple QRS configurations and had spontaneous cycle lengths (SCL) of 397 +/- 18 ms (n = 20) after 24 h of LAD occlusion and 446 +/- 23 ms (n = 20) after 48 h of LAD occlusion. Overdrive pacing did not result in the termination of the enhanced ventricular rhythm in any experiment. Propranolol, as a cumulative dose of 1.5-2.0 mg/kg i.v., also did not abolish the enhanced ventricular rhythm. In 24-h infarcted hearts, lidocaine abolished the enhanced ventricular rhythm in 1 of 11 experiments. In the remaining 10 experiments, the ventricular SCL was increased from 401 +/- 22 to 491 +/- 26 ms after a cumulative dose of 8.8 +/- 0.7 mg/kg of lidocaine. In the presence of verapamil, given as a cumulative dose of 0.60 +/- 0.11 mg/kg, the ventricular SCL was increased from 401 +/- 33 to 482 +/- 64 ms (n = 9). In 48-h infarcted hearts, lidocaine abolished the enhanced ventricular rhythm in 5 of 11 experiments. Both lidocaine and verapamil increased the SCL of hearts in which the enhanced ventricular rhythm persisted. Analysis of variance showed that only the increase in SCL by lidocaine in 48-h infarcted hearts was statistically significant. The atrial and idioventricular rhythms in noninfarcted hearts responded differently to lidocaine and verapamil. The results suggest that some electrophysiological effects of antiarrhythmic drugs in the normal heart may not be applicable to those in the diseased situation.     

The effect of K+ concentration on the energy metabolism in perfused rat heart

From experiments at various perfusion pressures in hemoglobin-free perfused rat hearts, oxygen consumption and redox shift of pyridine nucleotide were found to vary linearly with cardiac work. This relation was used for analysis of the energy metabolism associated with ion pumps. Mechanical activities such as left ventricular pressure and heart rate varied with the extracellular K+ concentration. Ion-pump dependent changes in oxygen consumption and redox state of pyridine nucleotide, estimated as the difference of the values at normal (4.7 mM) and various other extracellular K+ concentrations with corrections for the change due to mechanical work, were found to vary linearly with the K+ concentration. The slope for oxygen consumption was about 0.1 mumol/min/g X wet wt per mM K+. Lactate release changed markedly but transiently, about 1 min after changing the extracellular K+ concentration, and its amount varied linearly with the K+ concentration. In the steady state, however, lactate release was almost independent of the extracellular K+ concentration, although oxidized pyridine nucleotide increased with increasing K+ concentration. Coronary flow increased with the extracellular K+ concentration. Heart rate changed little between 1 and 12 mM K+, but decreased sharply above 12 mM K+. At 20 mM K+, heart beat was arrested and approximately 40% of myoglobin was deoxygenated. The intracellular oxygen concentration was estimated to be about 10 microM even during aerobic perfusion. Similarly, Ca2+-free arrested heart was found to be in a hypoxic state. The results showed that oxygen entry into cardiac tissue is facilitated by the cardiac cycle.     

The effect of fasting on D-3-hydroxybutyrate metabolism in the perfused rat heart

Summary The effects of fasting for 24 h and 48 h on D-3-hydroxybutyrate utilization and acetoacetate, L-lactate and pyruvate production by the isolated non-working perfused rat heart were investigated over a wide range of DL-3-HB concentrations. D-3-HB utilization is concentration dependent and shows saturation kinetics, D-3-HB oxidation is correlated with D-3-HB concentration. Acetoacetate production is proportional to DL-3-HB concentration. L-lactate production is proportional to DL-3-HB concentration up to 5 mM following a 24h fast and up to 10 mM after a 48h fast, but further increase in DL-3-HB concentration decreases the rate of lactate production. Fasting enhances D-3-HB utilization at 16 mM DL-3-HB by 16% and 25% in 24 h and 48 h fast respectively, but has no significant effect at lower concentration. Fasting has no effect on acetoacetate production. Fasting for 48 h doubled the half-saturation concentration (Ku) without significant change in the maximum rate of utilization (Vu) of D-3-HB.     

The effect of cigarette smoke on the metabolism of arachidonic acid to myotropic compounds in rat and hamster isolated lungs

Perfusion effluent from isolated rat and hamster lungs caused a relaxation of superfused strip of bovine coronary artery (BCA). This relaxation was abolished by pulmonary infusion of indomethacin. Pre-exposure of rats and hamsters to cigarette smoke during half an hour before the lung perfusion did not change the degree of this initial relaxation of BCA. Injection of 10 μg of sodium arachidonate (AA) into the pulmonary circulation of isolated hamster lungs caused a contraction of BCA, which was not changed by cigarette smoke pre-exposure. When AA (10 μg) was injected into the pulmonary circulation of isolated hamster lungs during cigarette smoke ventilation the contractions of superfused BCA and rat stomach strip (RSS) were not significantly different from those during the preceding and following air ventilation. In experiments with isolated rat lungs the initial relaxation of superfused BCA was accompanied by a contraction of superfused RSS. AA injection (10 μg) into rat lungs caused a further relaxation of BCA and contraction of RSS, which were abolished by pulmonary infusion of indomethacin. Cigarette smoke ventilation of isolated rat lungs caused a relaxation of superfused BCA, which was not abolished by indomethacin. During cigarette smoke ventilation injection of AA (10 μg) into the pulmonary circulation of rat lungs caused a relaxation of BCA and a contraction of RSS.The present study indicates that neither cigarette smoke ventilation nor pre-exposure to cigarette smoke has a drastic effect on the metabolism of arachidonic acid to myotropic compounds in isolated hamster and rat lungs.     

The effect of osmolarity on metabolism and morphology in adhesion and suspension chinese hamster ovary cells producing tissue plasminogen activator

The effects of constant osmolarity, between 300 and500 mOsm/kg, on the metabolism of Chinese HamsterOvary (CHO) cells producing tissue plasminogenactivator (tPA) were compared between adhesion andsuspension cultures. In both suspension and adhesionculture, the specific rates of glucose consumption(_G), lactate production (q_L), and tPAproduction (q_tPA) increased as osmolarityincreased, while these rates decreased when osmolaritywas higher than the respective critical levels. However, specific growth rate () decreased withincrease in osmolarity and this slope grew steeper inthe osmolarity range higher than the critical level. The decrease in in the adhesion culture was morerapid than that in the suspension culture. Thecritical osmolarity for adhesion culture (400 mOsm/kg)was lower than that for suspension culture (450 mOsm/kg). These results indicated that the adhesionculture was more sensitive to increase of osmolaritythan the suspension culture, while the specific ratesobtained from the adhesion cultures were in general1.5- to 3-fold higher than those obtained from thesuspension cultures. Cell volume increased asosmolarity increased in both the suspension andadhesion cultures, as reported previously forsuspension culture of hybridoma cells, but there wasno morphological change in the suspension culture. Incontrast, cell height decreased and cell adhesion areamarkedly increased as osmolarity increased in theadhesion culture. This morphological change inadhesion cultures may be one reason for the highersensitivity of adherent cells to the increase ofosmolarity than suspended cells.     

The effect of insecticides on Chinese hamster cell cultures

The effect of p,p′-isomers of DDT and its derivatives DDD, DDE and DDA on Chinese hamster cells in culture was studied. At different concentrations and various times of treatment the proliferation rate was inhibited most strongly by DDD and DDT, whereas DDE exhibited a markedly weaker influence. DDA was the least toxic compound of the four. The cytogenetic effects were also different. Again, DDA induced the least damage. Only enhanced gap rates but no chromosome breaks were observed. DDE was more active, and higher break rates occurred. DDD and DDT were by far the most damaging compounds, and they raised the gap and break rates markedly. However, no induction of configuration anomalies was found in any experiment.Chronic treatment of the cells for 3 months with DDT at 8 ppm did not alter the proliferation rate, the sensitivity to acute treatment with higher DDT concentrations or the chromosomal aberration rates.The results are discussed in relation to the relevance of differential pesticide effectivity in organs of higher animals and man.     

The effect of lidocaine on lysophosphatidylcholine-induced cardiac arrhythmias and cellular disturbances

The production of arrhythmias in the isolated heart by perfusion with lysophosphatidylcholine has been well documented. However, the role of the lysophospholipid as a physiological factor in the generation of cardiac arrhythmias is not clear. In this study, a pharmacological approach was used to delineate the physiological significance of lysophosphatidylcholine during this cardiac dysfunction. Lidocaine (5-20 mg/L) was found to be effective in the protection of the isolated rat heart from the lysophospholipid-induced arrhythmias at pharmacological concentrations. The effect of lidocaine in the protection of lysophospholipid-induced membrane dysfunction was studied with red blood cells. Lidocaine (2 mg/mL) protected red blood cells from hemolysis in the presence of lysophosphatidylcholine. Lidocaine did not inhibit the binding of the lysophospholipid to the red cell membrane, but inhibited hemolysis in a manner similar to cholesterol. The results are consistent with the postulate that lysophosphatidylcholine is a physiological factor in the pathogenesis of cardiac arrhythmias during myocardial ischemia.     

The effect of ACTH on HMG-CoA reductase activity in hamster adrenals

Injection to hamsters of various low doses of ACTH resulted in gradual increases in adrenal HMG-CoA reductase activity, in plasma and adrenal corticosteroid concentrations but produced no change in adrenal cholesterol content. These data indicate that under physiological conditions, ACTH could regulate HMG-CoA reductase activity through a mechanism which does no apparently involve a change in the cholesterol content of the gland.