Studying the influence of TaGW8 and TaGS5-3A genes on the yield of soft spring wheat in arid climate conditions of the Republic of Kazakhstan.

Drought is a primary ecological stress limiting wheat yield in water-deficient regions. Conducting targeted genetic selection of wheat cultivars can expedite the adaptation process of wheat to the climatic conditions of the region, allowing for the identification of high-yielding varieties with stable genetic traits. This study investigated the impact of the TaGW8 and TaGS3A genes, known for their contribution to wheat productivity. The effective productivity genes TaGW8-B1b/B1a and the TaGS5-3A-T genome exert a 32.8% influence on the variability of the 1000 grain weight (TGW) trait. This influence stems from both individual genes and their interactions, with at least 17.5% of TGW variability explained by the gene combinations examined in the study. Notably, the TaGS5-3A-T gene exhibits a significant positive correlation with total yield, exceeding 63%. The integration of these productivity genes, based on field phenotypic data, has resulted in an overall yield increase of selected samples by 0.8 tons/ha compared to the country's average multi-year indicator.

Mercury and selenium concentrations in lanugo of free-ranging California sea lions in the southern Gulf of California, Mexico.

Total mercury ([THg]) and selenium ([TSe]) concentrations were determined in California sea lion (Zalophus californianus) lanugo from the Gulf of California in 2021 and 2022. Relationships with sex, morphometrics, and year were evaluated. Following toxicological thresholds of concern for piscivorous mammals, most pups had a [THg] < 10 ppm, one pup (2021) had a [THg] > 20 ppm, no pups had a [THg] > 30 ppm. Females had significantly higher [TSe] than males; sex did not influence [THg]. [THg] and [TSe] in 2022 were significantly higher in the general population and male cohorts compared to 2021. Significant negative correlations were observed between [THg], [TSe], and morphometrics (2021). These results indicate that, compared to other pinniped species, regional California sea lions may have a decreased likelihood of experiencing Hg-related adverse health effects. Year-related changes in element concentrations suggest continued monitoring of this population to assess pinniped, environmental, and potentially, human health.

Indicators of oxidative stress in leukocytes isolated from bottlenose dolphins (Tursiops truncatus) in response to a proinflammatory challenge.

Few studies have analyzed the indicators of oxidative stress in marine mammals following exposure to lipopolysaccharides (LPS); sex and maturity-related differences have not been explored. The objective of this study was to compare the indicators of oxidative stress following exposure to LPS for 24 and 48 h in isolated Pacific bottlenose dolphin (Tursiops truncatus; N = 12) leukocytes in relation to sex and maturity stage, using spectrophotometry. Following 48 h under experimental conditions (10 µg LPS mL-1), the leukocytes from males (n = 5) produced significantly more superoxide radical (O2•-; F (1, 8) = 13.965, p = 0.006) and displayed significantly greater activities of catalase (CAT; F (1, 8) = 9.465, p = 0.015) and glutathione S-transferase (GST; p = 0.028) compared to the leukocytes from females (n = 7). Following 48 h under experimental conditions, maturity-stage did not significantly influence the indicators of oxidative stress. Mature bottlenose dolphins (n = 7) had a significantly higher average daily dietary intake compared to immature bottlenose dolphins (n = 5; F (1, 10) = 5.825, p = 0.036). These results suggest that sex-related strategies for coping with a proinflammatory challenge may be present within the leukocytes from bottlenose dolphins, while potential maturity stage-related strategies require further investigation.

Genotypic and ecological variability of zinc content in the grain of spring bread wheat varieties in the international nursery KASIB.

Spring bread wheat is the staple crop in Western Siberia and Kazakhstan, a signif icant portion of which goes for export. Wheat breeding with a high level of zinc in wheat grain is the most cost-effective and environmentally friendly way to address zinc def iciency in the diet. The purpose of this work was to evaluate the contribution of the factors 'location' and 'genotype' in the variability of zinc content in wheat grain, and to identify the best varieties as sources of this trait for breeding. The research on screening zinc content in the wheat grain of 49 spring bread wheat varieties from the Kazakhstan- Siberia Spring Wheat Trial (KASIB) nursery was carried out at 4 sites in Russia (Chelyabinsk, Omsk, Tyumen, Novosibirsk) and 2 sites in Kazakhstan (Karabalyk and Shortandy) in 2017-2018. The content of zinc in wheat grain was evaluated at the Ionomic Facility of University of Nottingham in the framework of the EU project European Plant Phenotyping Network-2020. The analysis of variance showed that the main contribution into the general phenotypic variation of the studied trait, 38.7 %, was made by the factor 'location' due to different contents of zinc and moisture in the soil of trial sites; the effect of the factor 'year' was 13.5 %, and the effect of the factor 'genotype' was 8.0 %. The most favorable environmental conditions for accumulation of zinc in wheat grain were observed in the Omsk region. In Omsk, the average zinc content in all studied varieties was 50.4 mg/kg, with 63.7 mg/ kg in the best variety 'OmGAU 100'. These values are higher than the target values of the international program Harvest Plus. 'Novosibirskaya 16' (49.4 mg/kg), 'Silach' (48.4 mg/kg), 'Line 4-10-16' (47.2 mg/ kg), 'Element 22' (46.3 mg/kg) and 'Lutescens 248/01' (46.0 mg/kg) were identif ied as being the best varieties. Signif icant possibilities for the production of wheat grain with high zinc content, which is in demand for the production of bread and pastry products with functional properties, were identif ied in the Western Siberian region.

A physical approach to model occlusions in the retinal microvasculature.

Blood occlusions in the retinal microvasculature contribute to the pathology of many disease states within the eye. These events can cause haemorrhaging and retinal detachment, leading to a loss of vision in the affected patient. Here, we present a physical approach to characterising the collective cell dynamics leading to plug formation, through the use of a bespoke microfluidic device, and through the derivation of a probabilistic model. Our microfluidic device is based on a filtration design that can tune the particle volume fraction of a flowing suspension within a conduit, with sizes similar to arterioles. This allows us to control and reproduce an occlusive event. The formation of the occlusion can be examined through the extracted motion of particles within the channel, which enables the assessment of individual and collective particle dynamics in the time leading to the clogging event. In particular, we observe that at the onset of the occlusion, particles form an arch bridging the channel walls. The data presented here inform the development of our mathematical model, which captures the essential factors promoting occlusions, and notably highlights the central role of adhesion in these processes. Both the physical and probabilistic models rely on significant approximations, and future investigation will seek to assess these approximations, including the deformability and complex flow profiles of the blood constituents. However, we anticipate that the general mechanisms of occlusion may be elucidated from these simple models. As microvascular flows in the eye can now be measured in vivo and non-invasively with single cell resolution, our model will also be compared to the pathophysiological characteristics of the human microcirculation.

Genetic markers and biochemical evaluation in the winter triticale identification and breeding.

Winter hexaploid triticale lines and cultivars were identified by protein (storage and enzyme) and DNA markers. The locus of B-Amy-2 and Adh-1 were characterized by two alleles, Mdh-1 by 3 alleles, B-Amy-1 and Mdh-2 by 4 alleles and the locus controlling cathodic peroxidase isozymes, a-amylase and esterase by 6, 9 and 12 alleles, respectively. Intra-and intervarietal variation, for the enzyme coding loci, gliadin and glutenine were found. According to the isoenzyme analysis and the grain quality lines 28 and 49 (softness, high amylose content: 28.9-25.6, protein: 11,6- 11,2% and albumin 50-43%) could be marked as genotypes suitable for brewing and were characterized by allele b-Amy-1-b. Genotypes 1420 and 1434 are good for bread making with a hardness index between 52 and 62 and a W value (alveograph) of 110- 120. Allele a-Amy-b is positively correlated with amylose content (r = 0.601) and negatively with protein content (r - 0.490), the correlation of the presence of allele 1-Amy-1-b and amylose content is r- 0.549. Three breeding lines had 40% amylose content in grain and flour. Furthermore, the presence of allele Mdh-1 was associated with a high content of glutenin (r = 0.568), and controlled by genes localized in a single linkage group. Also statistically significant correlations for Mdh-1 -a and Prx-D containing albumin to total protein (%) could observed. It was illustrated that the peroxidase activity and free proline content can be used as resistance markers to abiotic factors.

The effect of predator exposure and reproduction on oxidative stress parameters in the Catarina scallop Argopecten ventricosus.

Predation is known to impact growth and reproduction, and the physiological state of the prey, including its susceptibility to oxidative stress. In this study, we investigated how prolonged exposure to predators modulates tissue specific antioxidant defense and oxidative damage in the short-lived epibenthic scallop Argopecten ventricosus (2years maximum lifespan). Scallops that were experimentally exposed to predators had not only lower antioxidant capacities (superoxide dismutase and catalase), but also lower oxidative damage (protein carbonyls and TBARS=thiobarbituric acid reactive substances including lipid peroxides) in gills and mantle compared to individuals not exposed to predators. In contrast, oxidative damage in the swimming muscle was higher in predator-exposed scallops. When predator-exposed scallops were on the verge of spawning, levels of oxidative damage increased in gills and mantle in spite of a parallel increase in antioxidant defense in both tissues. Levels of oxidative damage increased also in the swimming muscle whereas muscle antioxidant capacities decreased. Interestingly, post-spawned scallops restored antioxidant capacities and oxidative damage to immature levels, suggesting they can recover from spawning-related oxidative stress. Our results show that predator exposure and gametogenesis modulate oxidative damage in a tissue specific manner and that high antioxidant capacities do not necessarily coincide with low oxidative damage.

Changes in oxidative stress parameters in relation to age, growth and reproduction in the short-lived catarina scallop Argopecten ventricosus reared in its natural environment.

Increase in oxidative damage and decrease in cellular maintenance is often associated with aging, but, in marine ectotherms, both processes are also strongly influenced by somatic growth, maturation and reproduction. In this study, we used a single cohort of the short-lived catarina scallop Argopecten ventricosus, to investigate the effects of somatic growth, reproduction and aging on oxidative damage parameters (protein carbonyls, TBARS and lipofuscin) and cellular maintenance mechanisms (antioxidant activity and apoptosis) in scallops, caged in their natural environment. The concentrations of protein carbonyls and TBARS increased steeply during the early period of fast growth and during reproduction in one-year-old scallops. However, oxidative damage was transient, and apoptotic cell death played a pivotal role in eliminating damage in gill, mantle and muscle tissues of young scallops. Animals were able to reproduce again in the second year, but the reduced intensity of apoptosis impaired subsequent removal of damaged cells. In late survivors low antioxidant capacity and apoptotic activity together with a fast accumulation of the age pigment lipofuscin was observed. Rates of oxygen consumption and oxidative stress markers were strongly dependent on somatic growth and reproductive state but not on temperature. Compared to longer-lived bivalves, A. ventricosus seems more susceptible to oxidative stress with higher tissue-specific protein carbonyl levels and fast accumulation of lipofuscin in animals surviving the second spawning. Superoxide dismutase activity and apoptotic cell death intensity were however higher in this short-lived scallop than in longer-lived bivalves. The life strategy of this short-lived and intensely predated scallop supports rapid somatic growth and fitness as well as early maturation at young age at the cost of fast cellular degradation in second year scallops.

Hypoxemic and ischemic tolerance in emperor penguins.

Oxygen store depletion and a diving bradycardia in emperor penguins (Aptenodytes forsteri) expose tissues to critical levels of hypoxemia and ischemia. To assess the prevention of re-perfusion injury and reactive oxygen species (ROS) damage in emperor penguins, superoxide radical production, lipid peroxidation (thiobarbituric acid reactive substances (TBARS)), and antioxidant enzyme activity profiles in biopsy samples from muscle and liver were determined and compared to those in the chicken and 8 species of flighted marine birds (non-divers and plunge divers). In muscle of emperor penguins, superoxide production and TBARS levels were not distinctly different from those in the other species; among the antioxidant enzymes, catalase (CAT) and glutathione-S-transferase (GST) activities were significantly elevated above all species. In the liver of emperor penguins, TBARS levels were not significantly different from other species; only CAT activity was significantly elevated, although GST and glutathione peroxidase (GPX) activities were 2-3 times higher than those in other species. The potential for ROS formation and lipid peroxidation is not reduced in the pectoral muscle or liver of the emperor penguin. Scavenging of hydrogen peroxide by CAT and the conjugation of glutathione with reactive intermediates and peroxides by GST and GPX appear to be important in the prevention of ROS damage and re-perfusion injury in these birds.

Diving seals: are they a model for coping with oxidative stress?

The diving lifestyle of seals depends upon cardiovascular adjustments that result in frequent vasoconstriction of numerous organs. With the first post-dive breath, reperfusion allows for eliminating accumulated carbon dioxide (CO(2)) and reloading oxygen (O(2)) stores. Reintroduction of oxygenated blood raises the potential for production of reactive oxygen species (ROS) and the possibility that they may overwhelm the antioxidant defenses. This study addresses the question of possible adaptive responses that allow ringed seal (Phoca hispida) tissues to tolerate repeated cycles of ischemia and reperfusion, and thus protect them from oxidative insult. We obtained samples of ringed seal heart, muscle and kidney through the cooperation of native subsistence hunters at Barrow, Alaska. Samples were subjected to oxidative stress by addition of xanthine oxidase. Production of superoxide radical (O(2)(.-)), lipid peroxidation (as determined by the presence of thiobarbituric acid reactive substances, TBARS) and antioxidant capacity (AOX) were quantified by spectrophotometric analysis. Similarly treated pig tissues were anticipated to be more susceptible to oxidative stress. Contrary to expectations, pig tissues revealed less O(2)(.-) and TBARS compared with ringed seal tissues. These results show that ringed seal muscle, heart and kidney can be induced in vitro to generate ROS, and suggest that the living seal's protective defenses may depend upon O(2)(.-) production, similar to the protective effect of experimental preconditioning, or on enhanced intermediate scavenging, as evidenced by the larger AOX found in ringed seal tissues.

Effects of arginine vasopressin in the heart are mediated by specific intravascular endothelial receptors.

Arginine vasopressin induces vascular, inotropic and arrhythmogenic effects in the heart. Existing evidence, obtained indirectly, suggests that these effects occur through paracrine endothelial mechanisms. To demonstrate this, vasopressin was confined to the intravascular space by covalent coupling to high molecular weight (2x10(6) Da, vasopresin-dextran) dextran. Isolated guinea pig hearts were infused with equivalent concentrations of vasopressin and vasopressin-dextran. The negative inotropic and coronary vasopressor effects of vasopressin-dextran were similar to those evoked by vasopressin; in both cases effects were reversible. Free dextran had no effect on vascular resistance nor in ventricular developed pressure. The inotropic and vascular effects of both vasopressin and vasopressin-dextran were blocked by the vasopressin receptor antagonist [Adamantaneacetyl(1), o-Et-D-Tyr(2), Val(4), Aminobutyryl(6), Arg(8,9)]vasopressin (Adam-vasopressin), indicating that the effects of the two agonists were vasopressin receptor-mediated. To elucidate possible endothelial intermediaries of these effects, isolated guinea pig hearts were infused simultaneously with vasopressin or vasopressin-dextran and several inhibitors either of synthesis or blockers of receptors of possible endothelial mediators. Only reactive blue 2, a P(2y) purinoceptor antagonist, and suramin, a P(2y) and a P(2x) purinoceptor antagonist, caused a total reversal of vascular and inotropic effects of vasopressin and vasopressin-dextran. Pyridoxalphosphate-6-Azophenyl-2'-4'disulphonic acid, a P(2x) purinoceptor antagonist, was without effect. Our results provide direct evidence that the short-term cardiac effects of vasopressin are due to selective activation of intravascular purinoceptors and suggest that an intermediary of these effects is ATP.

Plasma angiotensin II, arginine vasopressin and atrial natriuretic peptide in free ranging and captive seals and sea lions.

We used radioimmunoassay methods to quantify arginine vasopressin (AVP), atrial natriuretic peptide (ANP), and angiotensin II (Ang II) in plasma samples from harbor seals (Phoca vitulina richardsii), Weddell seals (Leptonychotes weddellii), northern elephant seals (Mirounga angustirostris), ringed seals (Phoca hispida), California sea lions (Zalophus californianus), and Steller sea lions (Eumetopias jubatus). Plasma concentrations of AVP, ANP, and Ang II in these pinniped species were within the ranges reported for other vertebrates under resting conditions. However, there were species, geographic and developmental variations in these hormones: Levels of AVP in plasma samples from adult Steller sea lions and harbor seals were higher than in pups of the same species; higher levels of plasma ANP were found in wild captured Alaskan Steller sea lions and in hunted ringed seals; differences in plasma levels of all three hormones were found throughout the geographic distribution of harbor seals and Steller sea lions in Alaska. This is the first report on circulating concentrations of vasoactive hormones in pinnipeds, and demonstrates that further studies are needed to ascertain the natural variability in these levels with the impact of molting, fasting, diving and environmental factors in seals and sea lions.

Changes in the plasma levels of vasoactive hormones during apnea in seals.

Prolonged and repetitive breath-hold periods (apnea) during and sleep are a routine component in the ecological physiology of marine mammals. Seals are among the few mammals in which control of heart rate (HR) can be studied independent of respiration, without pharmacochemical manipulation. We hypothesized that the vasoactive hormones angiotensin II (Ang II), arginine vasopressin (AVP), and atrial natriuretic peptide (ANP) were involved in the control of cardiovascular function in seals, and that the relationship was dependent upon input from the respiratory system. Venous plasma samples were collected and electrocardiograms were recorded from Northern elephant seal (Mirounga angustirostris) and Weddell seal (Leptonychotes weddellii) pups during both spontaneous breathing (eupnea) and apnea. Instantaneous HR and simultaneous plasma levels of ANP, AVP, and Ang II from periods of eupnea and apnea were compared. In these seal pups, apnea was associated with bradycardia, increased ANP, and decreased AVP and Ang II. The results support the hypothesis of a complex involvement between the vasoactive hormones and the control of cardiovascular function, and provide evidence for differential levels of control during periods of eupnea and apnea.

Plasma haptoglobin levels in threatened Alaskan pinniped populations.

We evaluated the plasma concentration of the acute phase protein haptoglobin (Hp) from Steller sea lions (Eumetopias jubatus) and harbor seals (Phoca vitulina) in regions of Alaska (USA) where the populations of these pinnipeds were declining and compared the values with concentrations of Hp from the same species in areas where the populations were stable. Samples were collected from 1992 through 1994 at sites in Southeast Alaska, Prince William Sound, the Gulf of Alaska, and the Aleutian Islands. Significantly higher levels of Hp were found in the samples from the areas of decline compared to those from stable populations. Based on these findings, we propose that one may be able to distinguish these compromised pinniped populations using Hp as a biomedical indicator.

Developmental changes in cardiorespiratory patterns of sleep-associated apnea in northern elephant seals.

The development of heart rate and respiratory patterns related to sleep-associated apnea were studied in northern elephant seal (Mirounga angustirostris) pups and adult males. Heart rate patterns became more refined in conjunction with an age-related increase in apnea duration in pups. That is, older pups showed significant sinus arrhythmia, while breathing and apneic heart rate were both stable and similar in magnitude to the sinus arrhythmia minimum. By contrast, younger pups showed poor or nonexistent sinus arrhythmia and shorter apnea durations with a variable and/or high heart rate during apnea. Apnea duration was positively correlated with the development of sinus arrhythmia and negatively correlated with both eupneic and apneic heart rate. Adult males showed extremely well-developed patterns of sinus arrhythmia and, in all cases, the minimum heart rate during the sinus arrhythmia was lower than the average heart rate recorded during apnea. These results suggest that seal pups are not born with the cardiac control associated with voluntary long duration apnea, but that apnea tolerance increases with refined cardiorespiratory control.

Effect of maternal aging on transgene heritability in transgenic founder mice derived from zygotes microinjected with retroviral long terminal repeat-containing recombinant deoxyribonucleic acid.

To determine the stability of artificially introduced recombinant DNA in the mouse germline throughout the reproductive life, founder mice derived from fertilized eggs injected with retroviral long-terminal-repeat-containing recombinant DNAs were mated with congenic FVB/N mice. Tail DNA of all progeny were screened and restriction fragment patterns of the transgenes were examined. Litter size and percentage of transgene transmission at various reproductive age periods were analyzed. Microinjection of 1737 eggs with four different recombinant DNAs resulted in 12 female and 11 male transgenic mice; 2 males were sterile and the remaining 21 mice served as founders to produce 1087 F1 progeny. With increasing parental age, litter size decreased generally. The percentage of progeny inheriting the transgenes declined markedly with increasing aging of 4 female founders; this aging effect was not observed in male founders (p < 0.005). No apparent change in transgenes was detected in progeny from late reproductive stages.

[Immediate and one-year evaluation of the benefit of aortic valvuloplasty in aortic stenosis with impaired ejection fraction]. / Evaluation immédiate et à un an du bénéfice apporté par la valvuloplastie aortique dans le rétrécissement aortique à fraction d'éjection basse.

Seventy-two consecutive patients with severe aortic stenosis and impaired by left ventricular ejection fractions (EF less than 40%) underwent percutaneous aortic valvuloplasty between September 1985 and November 1987. Forty-five patients had been turned down by the surgeons because of their age (29 patients over 80 years of age), their impaired left ventricular function or associated pathologies. Valvular dilatation with 15 to 23 mm diameter balloons resulted in a reduction of the transvalvular pressure gradient from 63 +/- 21 to 26 +/- 11 mmHg (p less than 0.001) and an increase in valve surface area from 0.48 +/- 0.15 to 0.91 +/- 0.32 cm2 (p less than 0.001) but with large individual variations. No cases of aggravation of associated aortic insufficiency were observed after the procedure. One 98-year old woman died during the dilatation and 4 other patients died during the hospital period. Immediate clinical improvement was observed in 80 per cent of patients. During the one-year follow-up period, 33 patients died, 31 of cardiac causes. Of the 34 survivors at one year, 21 had maintained their clinical improvement. A repeat hemodynamic study was performed in 22 patients 7 months after valvuloplasty. Eleven patients had restenosed and their hemodynamic parameters had practically returned to pre-valvuloplasty values. The left ventricular ejection fractions of the 11 patients without restenosis had increased from 28 +/- 7 to 40 +/- 18 per cent (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A one-step, low background coomassie staining procedure for polyacrylamide gels.

Present Coomassie staining procedures require hours of destaining and/or have high backgrounds. This one-step staining procedure is easier, gives lower background with no loss in sensitivity, uses less chemicals, requires less time, and can be followed by silver stain if increased sensitivity is desired after analyzing the results.

Percutaneous balloon valvuloplasty in patients with severe aortic stenosis and low ejection fraction. Immediate results and 1-year follow-up.

The efficacy, morbidity, and 1-year follow-up of balloon aortic valvuloplasty in patients with low ejection fraction (less than 40%) were studied on a consecutive series of 55 patients (mean age, 77 years) treated from September 1985 to February 1987. Because of their age (20 patients greater than 80 years old), poor left ventricular function, and associated diseases, 45 patients were definitely not surgical candidates. Balloon dilatation with 15-23-mm diameter balloon catheters decreased the transvalvular gradient from 66 +/- 24 to 28 +/- 14 mm Hg (p less than 0.001) and increased the valve area from 0.47 +/- 0.15 to 0.83 +/- 0.27 cm2 (p less than 0.001). Immediately after dilatation, ejection fraction mildly increased from 29 +/- 7% to 34 +/- 9% (p less than 0.001) in 38 patients who had undergone a second left ventricular angiogram after dilatation. No significant change in the degree of aortic regurgitation was found after the procedure. Three patients died in hospital (femoral arterial complications in two, septicemia in one). Immediate clinical improvement was noted in 80% of the patients. During the follow-up (mean, 11 months), 22 patients died (heart failure in 15 patients, sudden death in five patients, myocardial infarction in one patient, cancer in one patient). Thirty patients survived, 21 with persistent clinical improvement. Repeat cardiac catheterization was performed at 6 months in 20 patients, of whom eight had recurrence of symptoms. Nine patients had restenosis: their hemodynamic indexes had returned to prevalvuloplasty values.(ABSTRACT TRUNCATED AT 250 WORDS)

[Systemic and coronary hemodynamic effects of intravenous nicardipine at rest and in ischemia induced by rapid atrial stimulation]. / Effets hémodynamiques généraux et coronariens de la nicardipine intraveineuse au repos et lors de l'ischémie déclenchée par la stimulation auriculaire rapide.

The systemic and coronary haemodynamic effects of intravenous nicardipine were investigated in 10 patients with a more than 70 p. 100 stenosis of the left coronary artery. Two brief atrial pacing tests (ST1 and ST2) were performed. ST2 was performed 30 minutes after an intravenous injection of nicardipine 2.5 mg over 5 minutes. Nicardipine produced a 25 p. 100 decrease in ventricular systolic pressure and a substantial increase in cardiac index (from 2.74 +/- 0.48 to 3.46 +/- 0.35 l/min/m2, p less than 0.001). Measurement of the coronary flow rate by the thermodilution method showed a 40 p. 100 increase in sinus blood flow while coronary resistance decreased not only in territories with normal supply but also in myocardial territories distal to the coronary stenosis (from 2.76 +/- 2.3 to 1.83 +/- 1.5 mmHg/ml, p less than 0.02). With the same paced heart rate the ventricular function parameters were significantly improved during ST2 (cardiac index ST2 3.56 +/- 0.65 vs ST1 2.8 +/- 0.48, p less than 0.001; dp/dt max ST2 2143 +/- 369 vs ST1 1874 +/- 301 mmHg/sec, p less than 0.05), reflecting a lower degree of myocardial ischaemia. This was confirmed by the lower amplitude of electrocardiographic depression and by a higher lactate extraction coefficient (LE ST1 6 +/- 7 p. 100 vs LE ST2 12 +/- 12 p. 100, p less than 0.05). Mean arterial blood pressure and coronary sinus blood flow rate values were identical during the two atrial pacing tests.(ABSTRACT TRUNCATED AT 250 WORDS)