The effect of oxytocin on contractile responses and 45Ca movements in rat isolated aortic strips.

The effects of oxytocin (Oxt) on contractile responses and transmembrane Ca fluxes were studied in rat isolated aortic strips. Oxt (50-1000 mu ml-1) induced a dose-dependent contractile response and spontaneous myogenic activity. The Oxt-induced contractile response was not inhibited by pretreatment of aortic strips with phentolamine plus practolol, atropine, diphenhydramine plus cimetidine or indomethacin, but was significantly reduced by verapamil or deamino-ethyl-Oxt. The dose-response curve for Oxt was shifted upwards and to the left by increasing the Ca concentration of the medium from 1.8 to 4 mM. Oxt also shifted upwards the dose-response curve to Ca (1 to 5 mM) in aortic strips incubated in K depolarizing Ca-free media. Oxt increased the La3+-resistant 45Ca content without altering 45Ca efflux. The present results suggest that in rat isolated aortic strips Oxt produces a contractile response which, as previously found with other neurotransmitters, can be partly attributed to an increase of Ca influx through receptor-operated channels and to the release of Ca from intracellular stores.

The mechanism of the positive inotropic action of ketamine on isolated atria of the rat.

1 The effect of ketamine (10-7 M-5 X10-4 M) on electrical and mechanical properties of isolated atria of the rat was investigated. 2. On spontaneously beating right atria, ketamine produced a dose-dependent positive inotropic effect which was accompanied by a progressive reduction in atrial rate. 3 In electrically driven left atria, ketamine produced a dose-dependent positive inotropic effect which was accompanied by a parallel increase in df/dtmax and by a prolongation in the time to peak tension and in the time for total concentration. The positive inotropic effect occurred concomitantly with an increase in the height and duration of the plateau phase of the action potential of atrial fibres. 4 The positive inotropic effect of ketamine varied with the concentration of Ca and Na in the bathing media and the rate of stimulation. 5 Ketamine decreased post-extrasystolic potentiation and the amplitude-interval relationship. 6 The positive inotropic effect of ketamine was inhibited by verapamil (10-6 M) and by caffeine (4 X10-3 M). 7 Ketamine, 5 X10-5M and 10-4M, increased 45Ca uptake in electrically driven left atria. At 10-4M and 5 X10-4M, ketamine also increased 45Ca efflux. 8 These results suggest that ketamine produces its positive inotropic effect by two possible mechanisms. One of these is presumed to be an effect on the cell membrane with leads to an increased Ca influx into atrial fibres; the other is probably related to the inhibition of Ca sequestration by the sarcoplasmic reticulum.

Protective effects of dazmegrel on the PAF potential of ouabain-induced cardiac arrhythmias.

The ouabain threshold to induce cardiac arrhythmias in urethane-anaesthetized guinea-pigs was not modified by the administration of either dazmegrel, 4 mg/kg i.v., or lysine-acetylsalicylate, 13.5 mg/kg i.v., 5 min before the infusion of ouabain,10g/kg per min i.v. The previous administration of platelet-activating factor (PAF), 0.01 to 1 nmol/animal i.v., 2 min prior to ouabain, caused a significant, dose-dependent decrease of the ouabain threshold for the cardiac rhythm disturbances. Lysine-acetylsalicylate lacked any effect on this PAF potentiation. Pretreatment with dazmegrel 5 min before PAF, 0.05 nmol/animal i.v., abolished the PAF potentiation of the digitalis-induced arrhythmias. These results suggest that thromboxane synthesis is involved in this PAF effect and indicate an ability of PAF to induce thromboxane generation even in the case of cyclooxygenase inhibition.

Comparison of three beta-amino anilides: IQB-M-81, lidocaine and tocainide, on isolated rat atria.

The effects of a new beta-amino anilide, IQB-M-81, on electrical and mechanical activity of isolated rat atria were studied and compared with those of lidocaine and tocainide. In spontaneously beating right atria IQB-M-81 produced a dose-dependent decrease in rate, contractile force and maximum following frequency and prolonged the sinus node recovery time and the effective refractory period of atrial fibers. The negative inotropic effect was not modified by pretreating the atria with atropine or practolol. In isolated right atria IQB-M-81 did not block the positive chronotropic and inotropic responses to isoprenaline but shifted the dose-response curve to the right. IQB-M-81 and lidocaine, but not tocainide, reduced in a dose-dependent manner the slow contractions induced by isoprenaline in K-depolarized right atria. These results suggest that in contrast to other beta-amino anilides, IQB-M-81 exerted a negative chronotropic effect and that it presented a class I antiarrhythmic effect on isolated rat atria. A possible class IV antiarrhythmic effect is also discussed.

Electrophysiological effects of platelet-activating factor (PAF-acether) in guinea-pig papillary muscles.

The effects of PAF-acether (10(-11) to 10(-7) M) were studied on the electrical and mechanical activity of guinea-pig papillary muscles. At 10(-11) M PAF-acether did not modify the amplitude and Vmax of the upstroke or the resting membrane potential. At higher concentrations PAF-acether produced a dose-dependent increase in the amplitude and Vmax of the upstroke, shortened the action potential duration and hyperpolarized the resting membrane potential. These effects were accompanied by a biphasic effect on ventricular contractile force. The shortening of the APD was inhibited in muscles pretreated with tetraethylammonium or verapamil. In papillary muscles depolarized by 27 mM K Tyrode solution PAF-acether induced slow action potentials which were blocked by verapamil. PAF-acether produced a dose-dependent increase in amplitude and Vmax of the upstroke on the slow action potentials elicited by isoproterenol, prolonged the action potential duration and hyperpolarized the resting membrane potential. These results suggest that in guinea-pig papillary muscles PAF-acether increased Ca influx via the slow inward current.

Effects of pincainide on contractile responses and 45Ca movements in rat isolated vascular smooth muscle.

The effects of pincainide, a new beta-amino anilide, on contractile responses and 45Ca fluxes were studied in rat aorta and on spontaneous mechanical activity in rat portal veins. Pincainide (10(-5) to 10(-2) M) produced a dose-dependent inhibition of noradrenaline (NA) and high K+ -induced contractions. These inhibitory effects were observed with pincainide added either before or after the induced contractions. The Ca2+ -induced contractions of K+ -depolarized aorta as well as the spontaneous mechanical activity of portal veins were also inhibited by pincainide. Pincainide (5 X 10(-3) M) inhibited the 45Ca influx stimulated by 10(-6) M NA and increased 45Ca efflux. It was concluded that in isolated rat aorta, pincainide not only inhibited the influx of Ca2+ reducing the contractile responses to NA and high K+ but it also inhibited other effects related to NA-induced release of intracellular Ca2+ stores.

Lack of platelet-activating factor release on acute myocardial ischemia in the isolated interventricular septum of rabbit heart.

The effects of platelet-activating factor (PAF) on myocardial injury after 1 h global ischemia-30 min reperfusion were investigated in isolated arterially perfused interventricular septum of rabbit heart. PAF did not significantly affect developed tension, +/- dT/dtmax, resting tension and the times of active state in non-ischemic septa. The recovery of developed tension was significantly reduced by PAF (100 nM), after an ischemia-reperfusion challenge, from the control value of 20.9 +/- 3.5% to 10.5 +/- 1.8%, without a change in the resting tension (15.7 +/- 2.8 vs. 15.6 +/- 1.3 g). BN 52021 (20 microM), alone did not modify either parameter of ischemic damage, but antagonized the aggravating effect of PAF. Evidence of PAF activity was not found in any of the samples of the effluent perfusate obtained from ischemic control experiments. On the basis of the present results, we suggest a direct role for PAF in aggravating the myocardial damage induced by ischemia, and discard heart cells as the source of PAF in this state.

Negative inotropic effect induced by diethylamiloride (DEA) in rabbit myocardium.

The effects of the Na+/H+ exchange blocking drug diethylamiloride (DEA) on mechanical function have been studied in the rabbit isolated, arterially perfused interventricular septum. At concentrations of 10(-6)-10(-5) M, DEA induced a significant, dose-dependent, negative inotropic effect (a 54% decrease from control values at the highest concentration), which was slow to develop. After a 45 min washout, recovery was almost complete (95 +/- 3.4%). At concentrations greater than 5 x 10(-5) M, DEA induced a rapid and marked decrease in developed tension, associated with a progressive decrease in excitability and incomplete recovery. Resting tension was not significantly modified at any of the concentrations tested. At greater than 10(-6) M DEA enhanced significantly the transient negative inotropic effect of the brief intracellular acidosis induced by removal of NH4Cl perfusion, both by decreasing the minimal value of developed tension and by increasing the time required to produce this effect. These effects suggest that the dose-dependent DEA negative inotropic effect could be mediated by a progressive intracellular acidosis produced by inhibition of the Na+/H+ exchange system.

Effects of chlorbutol on 45Ca movements and contractile responses of rat aorta and its relevance to the actions of Syntocinon.

The effects of chlorbutol (0.7, 1.4 and 2.8 mM) on the contractile responses induced by KCl and noradrenaline (NA) and on 45Ca movements have been studied on rat isolated thoracic aorta. Chlorbutol decreased, in a dose-dependent manner, contractions induced by KCl and NA and this effect was observed whether it was added before or after the induced contractions. Preincubation with chlorbutol inhibited the contractile responses elicited by addition of Ca (1-5 mM) to Ca-free high-potassium solution. It also inhibited in a dose-dependent manner the 45Ca influx but increased 45Ca efflux in rat aortic strips. These results suggest that chlorbutol decreases peripheral resistance by reducing the availability of intracellular Ca to the contractile machinery in vascular smooth muscle cells. The effects of synthetic oxytocin (Syntocinon) at concentrations containing the same chlorbutol concentration were quantitatively similar from those produced by chlorbutol alone. Therefore, the inhibitory cardiovascular effects ascribed previously to synthetic oxytocin may be attributed to its preservative, chlorbutol, and not to oxytocin itself.

[Spanish research in international pharmacy and pharmacology journals from 1980 to 1989]. / La investigación española en revistas internacionales de farmacia y farmacología durante el período 1980-1989.

BACKGROUND: During the last years, the usefulness and validity of bibliometric analyses in complementing other types of indicators has been put forward. Especially interesting is the performance of this type of studies in the pharmacological area, due to the important medical and economic repercusions of the research in this field. METHODS: Documents of Spanish authors published in international pharmacological journals covered by the database Science Citation Index (1980-1989) were downloaded. Geographical and institutional distribution of the production, main publication journals and the basic or applied character of the research are some of the parameters analysed. The Expected Impact Factor (FIE) is used as an indicator of the potential influence of the research on the international scientific community. RESULTS: An exponential growth was detected for the number of Spanish publications in international journals of Pharmacy & Pharmacology during the period of 1980-1989. Universities were the most productive institutions, followed by hospitals, the Consejo Superior de Investigaciones Científicas, and industry, with only a small activity from private centers. Geographical distribution of production was very irregular, with Madrid, Barcelona and Valencia as the main productive cities. The increase in productivity was associated with a decrease over time in the FIE, although relatively high FIE journals were mainly used. Research in Pharmacy & Pharmacology showed as a mainly basic field, with a more clinical character for hospitals than for the remaining institutions. An increase in collaboration was observed, as supported by the increase in the coauthorship index, number of institutions per document and collaboration rate. CONCLUSIONS: The international visibility of the Spanish pharmacological research showed and important growth during this period. It was mainly a quantitative growth, since a higher impact or potential influence of the Spanish research over the international scientific community was not detected.

[Scientific activity of the most productive Spanish research teams in pharmacology and pharmacy during the period 1986-1993 as covered by the Science Citation Index (SCI)]. / Actividad científica de los grupos españoles más productivos en farmacología y farmacia durante el período 1986-1993 a través del Science Citation Index (SCI).

BACKGROUND: Bibliometric analyses at the research team level in the pharmacology and pharmacy (F&F) subfield allow in-depth analysis of the findings obtained at higher aggregation levels. MATERIAL AND METHODS: Publications of Spanish authors in pharmacological journals covered by the Science Citation Index (SCI) are studied and the most productive Spanish teams during 1986-1989 and 1990-1993 are identified through in-house programmes based on co-authorship analysis. Team composition is defined and team size, scientific output, productivity, expected impact factor and collaboration pattern of the most productive teams are analysed as well as its evolution over time. RESULTS: The observed annual increasing rate in the number of publications and authors in the field (11%) was similar to that of the number of researchers in the Spanish scientific system (8%). The number of highly productive teams doubled from the first to the second period (28 and 61 teams, respectively). The average team size was 8 researchers, showing an average scientific output of 3 documents/year and an average, productivity of 1.7 publications per author and team in each period. Over the years, an increase in the expected impact factor (EIF) of the publication journals and significant changes in the team composition were observed. A total of 13 stable teams were identified, with a greater size and output than the rest of the groups, and showing an upward trend in their expected impact factor and international collaboration rate. Stable teams did not show the negative correlation between team size and productivity observed for the total of the highly productive teams. CONCLUSIONS: The F&F subfield is in a very dynamic stage, with a great increase in the number of researchers, starting of new teams and consolidation of others. A trend was observed towards the concentration of activity in the most productive teams, that are the most visible internationally both in number of publications in the SCI and in the impact factor of the publication journals.

Protective effects of cyclopiazonic acid on ischemia-reperfusion injury in rabbit hearts.

The cardioprotective effects on myocardial ischemia of the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA) inhibitor, cyclopiazonic acid (CPA), were studied. We used the isolated arterially perfused interventricular septum of the rabbit heart submitted to 30-min global ischemia/30-min reperfusion. Mechanical [maximal increase in resting tension (MIRT), and the recovery of developed tension (RDT)], and biochemical parameters [creatine phosphokinase activity (CPK) in the effluent] were analyzed. CPA, 1 microM, perfused 30 min before the ischemia intervention significantly increased RDT by 54% and lessened MIRT by 66%. CPA also decreased CPK in the perfusate by 67.7 and 71.4% at 0-2 and 5-7 min of reperfusion, respectively. No additional benefits were shown either when the drug was perfused, both during ischemia and reperfusion, or with higher CPA concentrations (10-30 microM). The CPA cardioprotection was lost when the drug was present only during the reperfusion period. CPA exhibits functional and biochemical cardioprotective effects on myocardial ischemia. We postulated a decreased SR calcium contribution to the initial cytoplasmic calcium overload as the most probable mechanism involved.

Ultrastructural evidence of the protective effect of Na+/H+ exchange inhibition on the in vitro damage induced by ischaemia reperfusion in the interventricular septum of the rabbit heart.

We investigated the effects of the Na+/H+ antiporter inhibitor, dimethylamiloride, on myocardial injury after 1 h global ischaemia and 30 min. reperfusion in the isolated arterially perfused interventricular septum of the rabbit heart. After ischaemia and reperfusion challenge, dimethylamiloride significantly increased the recovery of developed tension in a dose-dependent manner, and significantly decreased the maximal increase in resting tension. Ultrastructural analysis of myocytes submitted to the experimental in vitro model supported functional maintenance of physiologically-like conditions. Where myocardial portions were submitted to ischaemic conditions and reperfusion, myocyte cell damage reached usual characteristics of infarct-like induced lesions. Intracellular oedema, severe disruption of myofibrils with loss of muscle striation and both swelling and fragmentation of mitochondria were the main characteristics observed. Dimethylamiloride treatment clearly modifies ultrastructural findings towards the normalization of cell shape and structure, only a slight-middle intracellular oedema and contraction bands were found. On the basis of the present results, we suggest that the protective effects exhibited by dimethylamiloride on the ischaemic myocardium are compatible with its Na+/H+ antiporter inhibition properties, they diminish Na+ accumulation and then either Ca2+ overload or non-exocytotic noradrenaline release during the ischaemia and reperfusion challenge.

Interaction of cocaine and bunaphtide on the 3H-norepinephrine uptake mechanism on isolated left atrium of guinea-pig.

Bunaphtide induces a blockade in the 3H-norepinephrine uptake and retention in the isolated guinea-pig left atrium. However, this blockade does not seem to be related with the cardiodepressant effect of the drug.

Effects of bunaphtine on 45Ca movements in rat aortic smooth muscle.

The effect of bunaphtine (BNA, 5 X 10(-5)M) on La3+ -resistant 45Ca content and 45Ca efflux was studied on rat aortic smooth muscle. BNA decreased both control and norepinephrine-stimulated La3+-resistant 45Ca content and increased the 45Ca efflux. These effects could explain the inhibition of the contractile responses induced by BNA.

Characterization of the calcium overload in cultured neonatal rat cardiomyocytes under metabolic inhibition.

We studied the calcium compartmentation of the Ca overload induced by 50 min of metabolic inhibition (MI) in cultured neonatal rat cardiomyocytes. MI was achieved by application of 1 mM iodoacetic acid (IAA) and 10 mM 2-deoxyglucose (2-DOG) with omission of glucose in the perfusate. MI per se abolished spontaneous beating, but 10 mM caffeine pulses at 15, 30 and 45 min were able to induce contractile responses. The contractile responses were abolished in the presence of Thg. After 20 min of MI, cells began to accumulate Ca. After 50 min of MI, the Ca exchanged via Na/Ca exchange (Na/Ca exchange-dependent Ca content) was increased by 3.21 +/- 0.15 mmol/kg dry weight (n = 5). The net increase remaining exchangeable via Na/Ca exchange represents 80% of the global net 45Ca uptake after 50 min in MI which was 3.98 mmol/kg dry weight, obtained in the "on-line" experiments. The release of this component of Ca is completed within 150s via Na/Ca exchange. There also was a 50% increase in the Ca content of the so-called "slow" compartment, 0.44 +/- 0.08 mmol/kg dry weight (n = 10) after 50 min under MI. The t1/2 of this compartment was 24.8 +/- 3.8 min typical of a mitochondrial origin in these cells. Thus 92% of the net Ca increase after 50 min MI remains exchangeable-80% of this is completed within 150s via Na/Ca exchange and 20% more slowly, t1/2 about 25 min. Cell ATP content, 27.35 +/- 2.07 nmoles/mg protein, was decreased after 10 min of MI to 2.25 +/- 0.29 nmoles/mg protein (n = 10) and remained close to this level after 20 min of MI (2.11 +/- 0.17 nmoles/mg protein; n = 6). It is to be noted that our results indicate no compromise of the Na/Ca exchange system after 50 min of MI although the global ATP is depleted in these cells.

Presence of a nitric oxide synthase inhibitor in the graft efflux during reperfusion in human liver transplantation.

Involvement of the nitric oxide (NO) system in complications following human orthotopic liver transplants (OLT) has been reported, but the contribution of the graft to the modulation of the NO system during reperfusion in normal OLT has not been characterized. We have studied the contribution of the graft efflux to the modulation of the NO system in 20 consecutive OLT. We evaluated its effects on isolated vascular reactivity of the rabbit and on rat cultured macrophages stimulated with lipopolysaccharide (LPS). In none of the donor liver biopsies was expression of inducible NO synthase (iNOS) activity by Northern or Western blot analysis found. Graft efflux after the onset of liver reperfusion, but not pre-transplant patient plasma, reversibly inhibited the acetylcholine-induced relaxation of norepinephrine-contracted rabbit aortic rings. Moreover, graft efflux reversibly inhibited NO production in rat macrophages treated with LPS, as evidenced by both a decrease in nitrite plus nitrate formation and a decrease in the production of [14C]citrulline from [14C]arginine. Addition of a 10% dilution of graft efflux to cultured rat macrophages incubated with LPS increased iNOS mRNA levels, suggesting direct inhibition of the enzyme but not of its expression. These results cannot be ascribed to the depletion of arginine the iNOS substrate since they can be reproduced even in the presence of an excess (10 mM) of exogenously added arginine. No correlation was found between the iNOS inhibitory activity in each sample and the corresponding clinical parameters related to either the graft function after the OLT or the existence of post-reperfusion syndrome. Our results indicate the existence of a soluble factor in the graft efflux from human OLT that reversibly and unspecifically inhibits NOS activity. Its involvement in the physiology and/or pathology of human liver diseases deserves further study.