Series Of Acute Experiments Research Articles

Long-Term Conditioning of a Donor Heart by Autoperfusion

The aim of research was to study parameters of homeostasis and conditions for stable operation of the autoperfused heart-lung complex ex vivo.Materials and methods. A series of acute experiments (n-3) was carried out to create a functioning heart-lung complex and study parameters of homeostasis ex vivo. A large mammal (mini-pig weighed 20-30 kg) was used as an experimental model. During the experiment, invasive blood pressure in the aortic root, pulmonary artery, central venous pressure, temperature of the left ventricle of the heart, gas composition of arterial blood (in the aortic root) and venous blood flowing from the coronary sinus was monitored.Results. The series of experiments evidenced the fundamental possibility of an isolated heart-lung complex ex vivo stable functioning. During 4-hours autoperfusion of the "heart-lung" complex, the parameters of hemodynamics, gas and biochemical blood composition remained within the reference values.Conclusion. The analysis of literature data and the results of experiments on laboratory animals allow us to state that the autoperfusion can be successfully used as an option of safe and long-term conditioning of a donor heart. This technique can be used to improve the results of heart transplantation with prolonged ischemia of the donor organ. Extending the survival of a donor heart ex vivo functioning will significantly expand the geography of donor bases, reducing the ischemic period to a minimum.

Test Procedure for a New Type of a Ventricular Assist Device Based on a Viscous Friction Pump

Introduction. Currently, the possibility of effective correction of multiple organ failure and increasing the life expectancy of patients with critical heart failure using the ventricular assist devices (VAD) is absolutely evidenced. The development of alternative analogues of such devices produced within the country has been an urgent problem for many decades. The design of this machine requires the development of a protocol for carrying out complex biomedical studies on the biocompatibility and safety of the new device.The aim of the study was to develop a protocol for testing and conducting comprehensive biomedical biocompatibility studies of a new ventricular assist device in an acute animal experiment.Materials and methods. The study to develop a technique for implanting a left-ventricular assist device (LVAD) in an acute experiment included female mini-pigs, weighed 40-60 kg. In a series of acute experiments, 5 implantations of a disk pump as a LVAD were performed with a maximum observation period equal 6 hours.Results. In the series of acute experiments, an implantation technique was developed and the fundamental possibility of a viscous friction pump application as a ventricular assist device was evidenced. In all experiments (n = 5), the average level of free hemoglobin did not exceed 2.6 mg%, which supports safety of performance of the viscous friction pump regarding blood erythrocytes. None of the experiments recorded episodes of pump shut-off or breakdown.Conclusions. The series of acute experiments on mini-pigs helped reveal a number of anatomical and physiological features of this animal species that significantly complicated implementation of persistent observation. However, the developed experimental LVAD test methodology can be recommended for use in further chronic experiments on large laboratory animals (calves).

Hydrodynamics in the intact and denervated aorta in experiment

Aim. As neurogenic processes affect the cardiovascular system and change its function throughout the whole life, the study aims to simulate and study the hydrodynamics of blood flow in an intact and denervated aorta.Methods. A pulse wave going through an intact segment of a dog’s thoracic aorta, a denervated autograft, and a donor dog’s thoracic aorta allograft was assessed by using equipment for blood pressure measurement and tensiometry of longitudinal and diametrical deformations of blood vessels at the point of pressure measuring. The experiments were performed under general endotracheal anesthesia. Two series of acute experiments on replacement of the thoracic aorta by an autograft and an allograft were carried out. Each series had eight dogs. The approach was thoracotomy in the IV intercostal space on the left. A required segment was replaced after heparin infusion while using subclavian-femoral bypass and retrograde autoperfusion.Results. It was found out experimentally that the formation and propagation of a normal isolated pulse wave with preservation of a viscous laminar blood flow were impossible without preserved innervation of the aorta. The experiments showed that in an intact aorta, its diameter tends to increase (by 400–500 μm), with simultaneous shortening of the segment (by 250 μm), and this process keeps being ahead of the pressure wave by 0.02–0.04 s. The rate of aortic dilatation is faster than that of systolic pressure elevation. However, in contrast to the intact aorta, the autograft, on the contrary, becomes longer and narrows, as pressure rises.Conclusion. To create optimal hydrodynamics of aortic blood flow, there should be a neuroreflectory system to control each pulse wave, which must determine its solitonic nature and provide antiflatter stabilization of blood flow.Received 16 April 2018. Revised 3 June 2018. Accepted 7 June 2018.Funding: The study did not have sponsorship.Conflict of interest: The authors declare no conflict of interest.

Acute Toxicity of Ammonia and Nitrite to Sea Bream, Sparus aurata (Linnaeus, 1758), in Relation to Salinity

AbstractSea bream, Sparus aurata, is one of the most important fish species that is commonly cultured in the Mediterranean and the eastern coasts of the Atlantic Ocean. The life cycle of sea bream in its natural habitat passes through hyposaline and hypersaline lagoons. It is important to determine the tolerance of the fish to nitrogenous compounds for aquaculture at maximum stocking densities. In the present study, a series of acute experiments were performed to evaluate the effect of salinity on ammonia and nitrite toxicity to sea bream. The fish were exposed to different ammonia and nitrite concentrations according to the static renewal methodology at three different salinities (10, 20, and 30 ppt) and at a temperature of 20 C and a pH of 8.2. The toxic effect of total ammonia nitrogen (TAN) and nitrite nitrogen (NO2‐N) decreased with increasing salinity levels (P < 0.001). Acute toxicity (96‐h lethal concentration 50 [LC50]) values of TAN were determined to be 5.93, 11.72, and 19.38 mg/L at 10, 20, and 30 ppt salinity, respectively. The 96‐h LC50 values of NO2‐N were determined to be 370.80, 619.47, and 806.33 mg/L at 10, 20, and 30 ppt salinity, respectively. Results indicate that sea bream is less tolerant to ammonia but more tolerant to nitrite compared with some other fish species.

Effects of N-methyl-d-aspartate receptor antagonism on neuroleptic-induced orofacial dyskinesias

Tardive dyskinesia is a syndrome of abnormal, involuntary movements, which occurs as a complication of long-term neuroleptic therapy. The pathophysiology of this potentially irreversible syndrome is still an enigma. The objective of the present study was to elucidate the role of N-methyl-D-aspartate (NMDA) receptor involvement in neuroleptic-induced orofacial dyskinesia in rats. Animals chronically treated with haloperidol for a period of 40 weeks exhibited significantly more vacuous chewing movements (VCMs), as compared to vehicle-treated controls. In a series of acute experiments, rats received: amantadine (10, 20, and 40 mg/kg i.p.), a low-affinity, uncompetitive NMDA-receptor antagonist (open channel blocker); dextrorphan (5, 10, and 20 mg/kg i.p.), an NMDA receptor channel antagonist; ifenprodil (2.5, 5, and 10 mg/kg i.p.), a noncompetitive allosteric NMDA receptor antagonist acting at the polyamine site; and Ro 25-6981 (2.5, 5, and 10 mg/kg i.p.), a potent and selective blocker of NMDA receptors which contain the NR2B subunit. All the drugs tested, except dextrorphan, reduced VCMs and tongue protrusions with varying efficacies and side effects profiles. Ro 25-6981 was found significantly more potent than amantadine and ifenprodil in reducing VCMs and tongue protrusions at all doses tested, and at the higher dose, it completely eliminated orofacial dyskinesia (p<0.05). These results suggest that NMDA receptors may play a significant role in the pathophysiology of tardive dyskinesia. Furthermore, antagonists showing selectivity for NMDA receptors containing the NR2B subunit may be particularly efficacious as novel therapeutic agents for the treatment of tardive dyskinesia and deserve further testing.

Role of stomach regions and duodenum in the formation of electrical activity of gastroduodenal complex.

Functional activity of components of the gastroduodenal complex (gastric cardia, gastric corpus, pylorus, and duodenal bulb) was studied in 4 series of acute experiments. One of these regions was subjected to electrical stimulation in each series. Our results suggest that the cardia possesses rhythm-forming properties, the corpus plays a system-organizing role, the pylorus plays a trigger role, and the duodenal bulb produce synchronizing effects.

Atrial fibrillation: a new explanation of the old phenomenon.

We propose a new mechanism of atrial fibrillation basing on the results of 30 series of acute experiments on anesthetized cats. In brief, combination of two or more arrhythmogenic factors shortens the interval between the inward and outward ionic currents in cardiomyocytes to a critical value. Under these conditions repolarization of cardiomyocyte membrane reaches the excitation threshold before complete inactivation of the depolarizing currents. This inevitably results in autoexcitation of myocytes (or extrasystole), that in turn promotes repolarization. Once occurred, autoexcitation turns into self-triggering activity resembling tachyarrhythmia paroxysm.

Effect of stimulation of the nucleus entopeduncularis on neurons of thalamic motor nuclei under normal conditions and after injury of the nigrostriatal dopaminergic system by the neurotoxin mptp

In two series of acute experiments on cats anesthetized with ketamine and immobilized with succinylcholine chloride, we investigated the reactions of neurons of the ventral anterior (VA) and ventral lateral (VL) motor nuclei of the thalamus to stimulation of the nucleus entopeduncularis (nEp) in intact animals and in animals administered the neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). It was established that in intact animals 28.0% of the investigated VA-VL neurons reacted to stimulation of nEp by inhibition with a latent period of less than 7 msec. In half of the inhibited neurons the first phase of inhibition, lasting 18 ± 2 msec on average, was followed by a second inhibitory wave lasting 25 ± 4 msec. In cats treated with MPTP the number of neurons inhibited after stimulating nEp practically did not change (24.5%). A tendency toward shortening of the first phase of inhibition and a statistically significant increase of the duration of its second phase (50 ± 11 msec) were noted. The changes in inhibitory processes in VA-VL neurons receiving afferents from nEp in cats with injury of the nitrostriatal dopaminergic system are explained by the more pronounced hyperplarization of the membrane of these neurons than in intact animals due to intensification of pallidothalamic inhibitory influences, which leads to weakening of Cl−-and strengthening of Ca2+-dependent K+ phase of postsynapic inhibition.

The effect of thromboxane inhibition on vulnerability to ventricular fibrillation in the acute and chronic feline infarction models

Inhibition of the enzyme that synthesizes thromboxanes may protect against the development of ventricular fibrillation (VF) during acute myocardial ischemia. This study was carried out to test this hypothesis with a new thromboxane synthetase inhibitor, and to extend the studies to alternative animal models of myocardial infarction. In a series of acute experiments, 19 cats were pretreated with 10 mg/kg of U-63557A (a dose that produced >75% reduction in thromboxane B 2 [TxB 2] levels) or saline before abrupt left anterior descending coronary artery occlusion. Seven of the nine control animals suffered spontaneous VF associated with a 77% fall in VF threshold compared with the treated animals, of which 2 of 10 had spontaneous VF and in which VF threshold fell by only 45% ( p < 0.025). Despite a similar extent of TxB 2 inhibition in another set of nine animals, U-63557A failed to protect against a fall in VF threshold during coronary reperfusion. Finally, chronic changes in VF threshold and inducibility of sustained ventricular tachycardia by programmed stimulation were assessed in a group of eight animals. The lowering of VF threshold and inducibility of ventricular tachycardia seen in the control state were not influenced by treatment with U-63557A. Thus protection against infarct-related VF by TxB 2 inhibition is a property shared by more than one pharmacologic agent. Arrhythmias generated by reperfusion or induced in a more chronic setting may not be thromboxane-dependent. These results have important implications for the planning of studies designed to assess the antiarrhythmic potential of drugs that inhibit thromboxane synthesis.

Identification of muscle spindles by direct and indirect electrical stimulation of intrafusal muscle fibers.

In two series of acute experiments on 25 anesthetized cats methods of rapid identification of muscle spindles based on electrical stimulation either of fusimotor nerve fibers or directly of the intrafusal muscle fibers were tested. The methods used are more reliable tests for the identification of muscle spindles than the generally accepted method of investigating the velocity of conduction of excitation along a single afferent fiber, for receptors both of the joints and of the deep tissues may also be innervated by fibers of the same diameter.

Modification of motor activity, passive avoidance conditioning and evoked potentials by microinjections of picrotoxin in both caudate nuclei in cats

Inhibition of movements is the result of the caudate nucleus (CN) activity. This action seems to be necessary for passive avoidance conditioning (PAC). Much data indicates that GABA has inhibitory effects in the CN. The present report provides further evidence for GABA inhibition in the CN. In cats, the acquisition session of a PAC response was carried out following the bilateral administration of 6 μg of picrotoxin or saline in the CN. Twenty four hours later (1st test session) the animals were placed in the security compartment and remained there during 600 sec. In the second test, the cats injected with picrotoxin crossed to the other compartment while the subjects injected with saline did not move. Another series of acute experiments were also carried out. Evoked potentials (EP) were recorded in the CN produced by nucleus centralis medialis electrical stimulation. After picrotoxin application the first and second peaks, which could represent EPSPs, increased while the third peak, which could represent IPSPs, decreased. In conclusion, it seems that GABAergic intracaudate transmission maintains a lower level of neuronal discharges and probably participates in the maintenance of a PAC but not in its acquisition.

Loss and recovery processes operative at the level of the cochlear microphonic during intermittent stimulation.

It has become increasingly apparent that the ear's behavior in response to intermittent stimulation is complex. In order to study the loss processes operative at the most peripheral level, CM sensitivity at the round window was monitored in a series of acute experiments on 150 cat ears as they were exposed to intermittent or continuous 5.0-kHz pure-tone stimulation. Stimuli were delivered at a SPL either 10 or 30 dB above that intensity necessary to produce a maximum CM output. Stimuli were on a 20% duty cycle with on-times varying from 10 msec to 2 min. Recovery processes taking place between stimuli were also measured. At all but the shortest on-times, loss was bimodally distributed, i.e., ears lost either much more or much less sensitivity than ears exposed to equivalent amounts of continuous stimulation. The shortest on-times, in contrast, tended to produce predominantly large losses. An early recovery process at the level of the CM was explored and found to have the following properties: it proceeded in log-time and the amount of recovery was proportional to the log of the on-time but was unrelated to the amount of residual sensitivity shift. The data were interpreted as showing the possibility that large losses to intermittent stimuli were likely to result when successive stimuli in the intermittent train interrupted the early recovery process before it has run to completion. These data were compared with TTS data from the human ear and parallels noted.

The induction of arrhythmias by sympathetic activity before and after occlusion of a coronary artery in the canine heart

Summary Stimulation of the left ansa subclavia before and after occlusion of the anterior descending artery of the dog's heart has produced significantly greater ventricular arrhythmia responses in the post-occlusion trials than in trials before occlusion. Data are presented from two series of acute experiments, Series 1 and Series 2 which include findings from 11 and 16 dogs, respectively. The experiments of the two series differed in types of electrical stimuli used and in elapsed time between occlusion of the artery and the first post-occlusion stimulation. All stimulations were applied when sinus rhythm was complete and no premature beats had occurred within a specified preceding duration. The arrhythmia responses in Series 1 were more intense (except that ventricular fibrillations were equal) and more prolonged than in Series 2. Reasons are discussed but not yet clear. The increased ventricular arrhythmia response persists strongly 5 days after occlusion. Propranolol, 0.5 mg/kg, blocked the arrhythmia response to sympathetic nerve stimulation completely during a period of 45–60 min after injection, but no blockade was apparent after 80 min. Possible mechanisms of origin of the induced arrhythmias were considered and evidence presented to indicate that individually generated discharges in ectopic pacemakers produced the arrhythmia in parts of the records and that reentry was the mechanism in other parts, particularly during approach to onset of ventricular fibrillation. The demonstration that brief periods of stimulation of sympathetic nerve strands to dog's hearts after coronary occlusion can produce ventricular arrhythmias of all degrees of severity including ventricular fibrillation suggests that emotional excitation of a myocardial infarction patient may induce similar ventricular arrhythmias and thereby place life in jeopardy.

The absorption of lactic acid from the reticulo-rumen of the sheep.

A series of acute experiments has been carried out on sheep to study some of the factors which influence the rate of absorption of lactic acid from the ligated washed�out forestomachs.

Elastase activity in human pancreatic secretions.

IN 1949, Balo and Banga1 first reported the isolation of the pancreatic enzyme elastase, which was unique in its ability to render soluble elastin (an important structural component of arteries, veins, skin and lung). This enzyme was first believed to be mucolytic in action, but it is now established that it is also a potent proteolytic agent2. Kokas, Foldes and Banga3, in a series of acute experiments, cannulated the main pancreatic duct of dogs and reported demonstrable elastolytic activity in canine pancreatic secretions. Grant and Robbins4 in a similar experiment reported that elastase in the pancreas is inactive. They hypothesize that the inactive ‘proelastase’ must be activated (by small amounts of crystalline trypsin or enterokinase) before elastolytic activity can be demonstrated.

The effects of whole bile and bile salts on the innervated and the denervated heart

The effects of the intravenous administration of whole bile and bile salts on the blood pressure and the electrocardiogram were studied in a series of acute experiments, under pentobarbital sodium (nembutal) anesthesia, on normal dogs and on dogs with denervated hearts; the same methods and technical procedures were employed in both cases. Similar observations were made over a period of several weeks on normal, trained dogs, and on one trained dog with a denervated heart; this permitted us to make repeated observations which could not have been influenced by anesthesia, operative trauma, or an accumulative effect of successive injections of bile. There were no detectable electrocardiographic differences between the effects of whole bile and bile salts on the innervated and the denervated heart; the irregularities and slowing of the rate of the heart were similar. During the period of gradual recovery from the hypotensive effect brought about by the first injections of bile constituents, the blood pressure of the dogs with denervated hearts usually did not return to its previous level, but the blood pressure of the dogs with innervated hearts, usually tended to do so. In both the normal animals and those with denervated hearts, approximately the same, gradual, hypotensive effect was produced by the intravenous administration of repeated doses of whole bile or bile salts. The injections finally led to failure of the heart, fall of blood pressure, and death of the animal. Our observations on the innervated heart differed so slightly from those on the denervated hearts of otherwise intact dogs to which whole bile or bile salts were administered intravenously, that it appears justifiable to conclude that whole bile and bile salts can produce practically the same hypotensive effect and cardiac changes, such as bradycardia and disturbances in rhythm, in the absence, as well as in the presence, of the cardiac autonomic nerves.