Cardiac vagal and sympathetic nerve responses to baroreceptor stimulation in the dog

The effects of ascending stepwise pressure changes in the isolated carotid sinuses on cardiac vagal and sympathetic nerve activities were studied in anesthetized, open chest dogs. The steady state responses of the cardiac vagal and the sympathetic nerve activity and arterial blood pressure were plotted against the sinus pressure and the relations were approximated by the normal distribution function (response curve). The sinus pressure- vs. reflex gain relations (reflex gain curve) were approximated by the normal density function. The maximum gain and the range of change were found to be greater for the vagal than for the sympathetic and arterial pressure responses. The sinus pressure values derived from response curves and reflex gain curves for vagal and sympathetic nerve responses were close to each other, while these values and those obtained from arterial pressure responses were considerably apart. It was concluded that: (1) The cardiac vagal neurons are more sensitive to the baroreceptor input than the sympathetic neurons; (2) The similar type of baroreceptor afferent inputs reach the cardiac vagal and the sympathetic structures which are controlling the autonomic outflows.     

Effect of posture on arterial baroreflex control of heart rate in humans

Summary Altered baroreflex function may contribute to the cardiovascular changes associated with weightlessness. Since central blood volume (CBV) increases during simulated weightlessness, we have examined the possibility that acute changes in CBV may modify baroreceptor function. We used graded head-up tilt (HUT) and head-down tilt (HDT) to induce changes in CBV, and neck suction to stimulte carotid baroreceptors, in 6 subjects. The increase in pulse interval induced by a negative pressure of 8.2 kPa (62 mm Hg) imposed for 10 s while supine was compared with the increase while tilted for 8 min at ± 15, ± 30 and ± 45. During HDT at 15 the pulse interval over the first 5 cardiac cycles following suction onset was 51 ± (SEM) 18 ms longer (p<0.05), at 30 it was 61±20 ms longer (p<0.05), and at 45 it was 74±35 ms longer (p<0.01), compared with supine. During HUT at 15 the pulse interval was 25±9 ms shorter (p<0.05) than when supine, but was not significantly different at 30 and 45. These responses occurred independently of changes in brachial blood pressure. Attenuation was also observed after 5 min (56±17 ms; <0.05), and after 40 min (25±9 ms; p<0.05) of 60 HUT compared with supine. We conclude that posture does modify arterial baroreflex control of heart rate. If this occurs primarily as a result of a change in CBV, then the acute effect of weightlessness may be an accentuation, not an attenuation, of baroreflex function.M. H. Harrison was a National Research Council postdoctoral research fellow on leave from the Ministry of Defence, UK     

Acute adaptation and resetting of the baroreflex control of vascular resistance in the canine hindquarters and mesentery

To determine whether acute adaptation and resetting occur in the baroreflex control of regional vascular resistance, experiments were conducted in anesthetized and vagotomized dogs. The carotid sinuses were vascularly isolated to regulate the carotid sinus pressure (CSP) in an open-loop fashion. The hindquarters (n= 12) and mesenteric (n=10) beds were perfused with constant flow and arterial perfusion pressures (HPP and MPP) were used to reflect changes in hindquarters and mesenteric resistance respectively. We first observed alterations in HPP and MPP during the course of CSP holding (conditioning pressure) at various levels for 15 min. Thereafter, the CSP was lowered to 50 mm Hg and increased stepwise to obtain the CSP-HPP and CSP-MPP baroreflex function curves. In experiments in the hindquarters bed, HPP stabilized at an average of 104.7 mm Hg during the initial conditioning pressure at 100 mm Hg. When conditioning pressure decreased to 50 mm Hg, the HPP increased to 125.5 mm Hg and then gradually declined to a steady level (115.6 mm Hg) in 5 min. An increase in conditioning pressure from 100 to 150 mm Hg caused HPP to decrease to 54.8 mm Hg followed by an upward adaptation to a steady level (80.2 mm Hg) in 5 min. The CSP/HPP curves constructed from the CSP step protocol were also affected by conditioning pressure. There were significant increases in the threshold and saturation pressures as conditioning pressure was elevated. However, the resetting was characterized by a parallel shift of the CSP/HPP curves without significant changes in baroreflex gain or sensitivity. Although the changes in mesenteric resistance in response to CSP changes were relatively weaker (lower gain), the phenomena of acute adaptation (MPP changes during 15-min conditioning pressure) and resetting (curve shift following different conditioning pressures) were still observed. In addition to the demonstration of adaptation and resetting of baroreflex control on the resistance in these two vascular beds, a graphical analysis is used to indicate that acute adaptation of the baroreflex responses is part of the resetting process. It is not necessarily associated with a decrease in sensitivity. Adaptation occurs as the baroreceptors recognize a new pressure in minutes and results from a shift of the HPP or MPP to a new level along the newly reset function curve.     

Über die Alterswandlung der elastischen Eigenschaften des Aorta-Iliaca-Rohres beim Menschen

Zussammenfassung Bei ca. 2500 Normo-, Hypound Hypertonikern wurde die Pulswellengeschwindigkeit (PWG) im Aorta-Iliaca-Rohr untersucht.Da die PWG vom Alter und vom Blutdruck beeinflußt wird, bezogen wir die PWG-Alterskurve der jeweils untersuchten Mitteldruckhöhe auf Blutdruckwerte, die von einem Dezennium zum anderen möglichst gleich waren. Dadurch wurden reine PWG-Alterskurven erreicht.Die bisher häufig beschriebene S-Form der PWG-Alterskurve stellt nach unseren Ergebnissen einen Überlagerungseffekt aus Alterund Blutdruck dar.Mit dem Blutdruck nimmt die Anstiegssteilheit der PWG-Alterskurven zu. Dies ist ein Hinweis für das schnellere Altern der Hochdruckaorten im Vergleich zu den Normaldruckaorten. Bei niederem Blutdruck ist der Altersgang langsamer als im Normaldruckbereich.Bei hohem Blutdruck nimmt ab dem 55. Lebensjahr die Anstiegssteilheit der PWG-Altersgruppe gegenüber den vorhergehenden Lebensjahren ab. Dies wird als Ausdruck einer Absterbeauslese der Hypertoniker gedeutet.Ein Wirksamwerden einer kollagenen Jacke ist innerhalb der von uns untersuchten Alters- und Druckgrenzen nicht feststellbar.

---

Summary The pulse wave velocity (PWV) was studied in the, aortic iliac vessel of approximately 2500 persons with normal, too high or too low blood pressure.Since the PWV is influenced by age and blood pressure we related the PWV age curve of the mean pressure value established to blood pressure values which remained as equal as possible from one decade to the next. We thus obtained pure PWV age age curves.The so frequently described S-shape of the PWV age curve according to our results represents a superimposed effect of ageand blood pressure. The steepness in rise of the PWV age curves increases with blood pressure. This points to the more rapid ageing of the high pressure aortas as compared to aortas with normal pressure values. In hypotension the age curve is less steep than in normal pressure ranges.In hypertension the steepness in rise decreases beyond the 55th year of life as compared to preceding years. This is explained by the mortality selection of the hypertensives.The collagenous jacket could not be determined within the ranges of age and pressure examined.

     

Effect of adrenoblockers of vascular responses during carotid sinus pressure reflexes

In acute experiments on cats using local anesthesia, listhenon, and artificial respiration, the blood pressure was recorded in the common carotid artery and the tone of the cerebral and femoral vessels was measured by a resistographic method. An increase in pressure in the isolated carotid sinuses was accompanied by a decrease in arterial pressure and tone of the femoral and cerebral vessels. When the pressure in the carotid sinuses fell, the arterial pressure and tone of the femoral and cerebral vessels rose. In both cases the response of the cerebral vessels was less marked than that of the femoral vessels. Blocking -adrenoreceptors with phenatolamine considerably weakened or completely abolished these responses; they were not affected by -adrenergic blockade with obsidan. The role of the carotid baroreceptors in the regulation of the cerebral circulation during orthostatic collapse is discussed.Department of Pharmacology, Pyatigorsk Pharmaceutical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 7, pp. 40–42, July, 1979.     

Characteristics of brachiocephalic and carotid sinus baroreceptors with non-medullated afferents in rabbit

The characteristics of brachiocephalic and carotid sinus baroreceptors with non-medullated afferents have been studied in rabbits. The conduction velocities of 18 non-medullated fibers arising from the brachiocephalic baroreceptors were 0.4-0.8 m/s (0.59 +/- 0.03 m/s, mean +/- SE) and their thresholds were 74-104 mmHg (84 +/- 2 mmHg). 29 non-medullated carotid sinus baroreceptor afferents had thresholds ranging from 60 to 125 mmHg (92 +/- 3 mmHg). Their conduction velocities were 0.5-1.1 m/s (0.65 +/- 0.05 m/s). Blood pressure-baroreceptor response curves of both the brachiocephalic and the carotid sinus baroreceptors were constructed. As the aortic arch non-medullated baroreceptor afferents, the brachiocephalic and the carotid sinus baroreceptors with non-medullated afferents exhibited thresholds about 30 mmHg higher than the medullated ones, considerably lower firing rates, comparatively rapid adaptation and remarkable irregular discharge pattern. It is suggested that the non-medullated baroreceptor afferents are of little importance for the cardiovascular regulation under normal conditions but are likely to play an important role during a sudden rise in arterial pressure.     

Two Mouse Lines Selected for Differential Sensitivities to β-Carboline-Induced Seizures Are Also differentially Sensitive to Various Pharmacological Effects of Other GABAA Receptor Ligands

Two mouse lines were selectively bred according to their sensitivity (BS line) or resistance (BR line) to seizures induced by a single i.p. injection of methyl -carboline-3-carboxylate (-CCM), an inverse agonist of the GABA_A receptor benzodiazepine site. Our aim was to characterize both lines' sensitivities to various physiological effects of other ligands of the GABA_A receptor. We measured diazepam-induced anxiolysis with the elevated plus-maze test, diazepam-induced sedation by recording the vigilance states, and picrotoxin- and pentylenetetrazol-induced seizures after i.p. injections. Results presented here show that the differential sensitivities of BS and BR lines to -CCM can be extended to diazepam, picrotoxin, and pentylenetetrazol, suggesting a genetic selection of a general sensitivity and resistance to several ligands of the GABA_A receptor.Personnalité et conduites adaptatives,     

Rate of decrease of myocardial O2 consumption due to cardiac arrest in anesthetized goats

The isolated and combined influence of cardiopulmonary and sinoaortic denervation on long-term blood pressure (MAP), heart rate (HR), plasma renin activity (PRA) and plasmavolume (PV) was studied in 11 conscious, chronically instrumented foxhounds receiving a normal sodium diet. MAP, HR, PV and PRA remained unchanged in the 5 dogs after bilateral thoracic vagal stripping, which eliminates the cardiopulmonary afferents. After sino-aortic denervation in another 5 dogs there was equally little change when compared to the control group. Only total baroreceptor and cardiopulmonary denervation (7 dogs) revealed significantly higher levels of MAP (119.6±4.6 vs. 100.4±1.5,P<0.01), HR (118.2±3.7; vs. 84.1±3.5;P<0.0001), and PRA (3.6±0.9 vs. 0.9±0.2;P<0.05). In conclusion, the function of either arterial baroreceptors or cardiopulmonary receptors is sufficient for normal circulatory control. When both groups of receptor afferents are interrupted, MAP, HR, and PRA rise to significantly higher levels. Thus, both systems interact in a sense of a nonadditive attenuation on cardiovascular centres. This may clarify previous disputes concerning neurogenic hypertension, and supplies information for the role of the renin-angiotensin system in blood pressure control.This study was supported by the German Research Foundation within the SFB 320, Heidelberg     

Sleep changes induced by the local application of 5,7-dihydroxytryptamine into the nodose ganglia and aortic denervation in the rat

The effects of a bilateral microinjection of 5,7-dihydroxytryptamine (5,7-DHT) into the nodose ganglia and aortic denervation on the daily amounts of sleep/wake states were studied in rats. Both lesions produced an increase in paradoxical sleep and provoked the onset of paradoxical sleep episodes without slow-wave-sleep transition (narcolepsy-like paradoxical sleep episodes). The increase in paradoxical sleep observed after 5,7-DHT injection was more important than that of the aortic denervation. In addition, both 5,7-DHT-treated and aortic-denervated animals exhibited a delayed decrease in slow-wave sleep associated with an increase in wakefulness. These results show that the peripheral messages coming from aortic serotonergic afferent fibres to the nucleus tractus soltarius play a modulatory role in the daily expression of paradoxical sleep in rats.     

Action ofγ-aminobutyric acid and its phenyl derivative on central links of vascular reflexes from aortic-carotid chemo- and mechanoreptors

Experiments on decerebrate cats revealed an inhibitory effect of -aminobutyric acid (GABA; 100–200 g/kg) and its phenyl derivative, phenyl-GABA (20 mg/kg), on depressor responses of the systemic arterial pressure and on inhibition of spontaneous electrical activity in the renal nerve arising in response to excitation of the carotid sinus mechanoreceptors and afferent fibers on the sinus and depressor nerves carrying impulses from mechanoreceptors. Pressor responses of the systemic arterial pressure and electrical activity evoked in the renal nerve by stimulation of the carotid sinus chemoreceptors were intensified after administration of the same doses of GABA and phenyl-GABA. The results are interpreted from the standpoint of the depriming action of GABA and its phenyl derivative on the paramedian reticular nuclei of the medulla.Paper read at the March, 1974 Meeting of the Volgograd Scientific Society of Pharmacologists.Department of Pharmacology, Volgograd Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 79, No. 4, pp. 71–75, April, 1975.     

Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non-pulsatile pressures in the dog

1. In the anaesthetized dog the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. When the vasosensory areas were perfused at non-pulsatile pressures within the normal physiological range of mean pressures, the reflex reduction in systemic vascular resistance produced by a given rise in mean carotid sinus pressure was significantly greater than that resulting from the same rise of aortic arch pressure.3. On the other hand, when the vasosensory areas were perfused at normal pulsatile pressures and within the normal physiological range of mean pressures, there was no difference in the size of the reflex vascular responses elicited by the same rise in mean pressure in the carotid sinuses and in the aortic arch.4. Whereas the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in pulse pressure, those evoked by the aortic arch baroreceptors through changes of mean pressure are only weakly affected by modifications in pulse pressure. Evidence for this was obtained from single stepwise changes of mean pressure in each vasosensory area during pulsatile and non-pulsatile perfusion, and from curves relating the mean pressure in the carotid sinuses or aortic arch and systemic arterial perfusion pressure.5. The vasomotor response elicited by combined stimulation of the carotid sinus and aortic arch baroreceptors was greater than either response resulting from their separate stimulation.6. When the mean perfusion pressures in the two vasosensory areas are changed together, the curve relating mean pressure to systemic arterial pressure during pulsatile perfusion of the areas is considerably flatter than that for non-pulsatile perfusion.7. Increasing the pulse pressure in the carotid sinuses or aortic arch caused a decrease in systemic vascular resistance, the response elicited from the carotid sinuses being the larger.8. Altering the phase angle between the pulse pressure waves in the carotid sinuses and aortic arch had no effect on systemic vascular resistance.9. In both vasosensory areas, increasing the pulse frequency caused a reduction in systemic vascular resistance.     

Studies on blood-pressure regulation by the use of a baroreceptor analog

Summary In rabbits anesthetized with urethane the aortic and carotid sinus nerves were stimulated by an electric baroreceptor analog. In closed loop experiments the analog buffered blood pressure alterations and alterations of heart rate following the blockade of aortic nerves and clamping the common carotid arteries. The carotid sinus nerves appeared to be not more sensitive to baropacing by the analog than the aortic nerves. Blood pressure and heart rate oscillations induced by vagal stimulation with the analog were damped and finally disappeared when the electric receptor analog was used to stimulate simultaneously the depressor nerves. Analysis of the baroreceptor analog in open loop experiments gave the same results as obtained on natural baroreceptors: pulse pressure sensitivity changed with mean pressure, amplitude, and pulse rate. The transfer function of the analog is the same as transfer functions of carotid sinus nerves are. It is concluded, that the baroreceptor analog may be useful for closed loop baropacing treatment of hypertension.This work was supported by the Deutsche Forschungsgemeinschaft (Ze 67/1).     

Analysis of hemodynamic responses to hypothalamic stimulation in waking animals

Experiments on waking cats showed that electrical stimulation of protective zones of the hypothalamus leads to development of hypertension and inhibits baroreceptor reflexes. In animals with divided carotid sinus and aortic nerves, threshold hypothalamic stimulation leads to the appearance of depressor responses, whereas above-threshold stimulation evoked depressor-pressor responses. It is suggested that depression of baroreceptor reflexes is one of the mechanisms of the development of hypertension in response to hypothalamic stimulation.Department of Experimental Physiology and Pharmacology, Central Research Laboratory, I. P. Pavlov First Medical Institute, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the SSSR N. P. Bekhtereva.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 9, pp. 281–283, September, 1979.     

Effects of sleep deprivation on the activity of selected metabolic enzymes in skeletal muscle

Summary The present study gives the results of a comparison of the recorded and true tibia-calcaneal angles in 17 normal subjects and in 14 patients with abnormally hypoextensible non contracting triceps. 1. For a minimal passive torque, the difference between true and recorded angles varied considerably from one individual to another. The means and ranges for the two groups were respectively: –8 (+7, –21) and –7 (+5, –20). 2. When the passive torque increased as a result of slow passive lengthening of the muscle, the true curve was steeper than the recorded one, owing to differences between the two angle measurements. For each of the two groups the differences in means and ranges were respectively: 6 (0, +13.5) and 8 (3, 12). 3. Subjects made isometric voluntary contractions of the triceps surae at fixed angles which corresponded to step by step muscle lengthening. The resulting true curve was much steeper than the recorded curve. The differences in means and ranges were: 7 (1.5, +15) in children of the two groups and respectively 3 (0, +9) and 12 (10, 14) in adults of the two groups. The present results show that this methodology was the only reliable way of correctly obtaining passive and active torque-angle curves, measuring differences between subjects, appreciating the effects of treatments and these by ascertaining whether or not trophic muscle regulation was defective.     

The autoregulation of the heart work by the coronary perfusion pressure

Summary In 9 dog hearts (coronary arteries cannulated, aortic blood pressure allowed to change) an increase in coronary perfusion pressure raised the peak pressure in the left ventricle and the maximum ofdp/dt, while the left ventricular enddiastolic pressure decreased.An enhancement of coronary perfusion pressure in 6 dog hearts (coronary arteries cannulated, aortic blood pressure kept constant) increased the peak pressure in the left ventricle and the maximum ofdp/dt; the left ventricular enddiastolic filling pressure decreased.This coronary perfusion pressure-induced increase in heart performance can also be shown by ventricular function curves. These are relatively flat at low coronary pressures. Therefore, even large changes in left ventricular enddiastolic pressure bring about only a small increase in stroke work. Heart failure could not be observed at low coronary perfusion pressures. An increase in coronary perfusion pressure shifted the ventricular function curves to the left, so that even a small change in enddiastolic filling pressure had a great effect on strokework.The homeometric autoregulation of the heart can be explained to a certain part by the coronary perfusion pressure.There is no explanation of the effect of the coronary perfusion pressure on heart performance. Based on our findings it must be concluded that an increased coronary perfusion pressure distends the coronary arteries (garden-hose-effect), which increases myocardial fiber tension and heart performance.Supported by the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich Cardiologie Düsseldorf).     

Effects of calcium channel blockers on isolated carotid baroreceptors and baroreflex

Our study determined the effects of the calcium antagonists, nifedipine and verapamil, on the carotid sinus baroreceptors and baroreflex. The left carotid sinus region in dogs was vascularly isolated and filled with oxygenated physiological salt solution. Steady-state multiunit activity was recorded from the carotid sinus nerve for sinus pressures of 50-200 mmHg after bathing the carotid sinus region in a solution containing no drug, 10 micrograms/ml nifedipine (n = 6), or 5 micrograms/ml verapamil (n = 5). The slopes of the curves relating carotid sinus nerve activity (% of maximum control) to carotid sinus pressure were control, 0.81 +/- 0.06; nifedipine, 1.29 +/- 0.14; and verapamil, 0.48 +/- 0.06%/mmHg, indicating that nifedipine increased and verapamil decreased the sensitivity of the carotid sinus baroreceptors. Additional studies with bilateral carotid sinus isolation (carotid sinus nerves intact) indicated that nifedipine enhanced and verapamil attenuated carotid baroreflex control of renal sympathetic nerve activity. Pressure-volume curves generated in the isolated carotid sinus showed that effects on smooth muscle do not account for the opposing effects of the two Ca2+ antagonists. Omitting Ca2+ from the physiological solution resulted in increased carotid sinus nerve activity, an effect blocked by verapamil but not nifedipine. Verapamil, but not nifedipine, inhibited veratrine-induced (Na+-dependent) excitation of carotid baroreceptors. Thus the excitatory effects of nifedipine on the carotid sinus baroreceptors are dependent on Ca2+ mechanisms, whereas the inhibitory effects of verapamil may be due mainly to interference with the inward Na+ current.     

Production of tumor necrosis factors by human T cell lines infected with HTLV-1 may cause their high susceptibility to human immunodeficiency virus infection

The production of tumor necrosis factor (TNF)- and TNF- by various human hematopoietic cell lines was quantitatively examined using a highly sensitive radioimmunoassay specific to TNF- or a cytolytic assay performed with mouse L929 cells. It was found that the HTLV-1-infected T cell lines examined produced large amounts of both TNF- and TNF-. In particular, interleukin-2 (IL-2)-dependent cell lines produced large amounts of TNF-. In contrast, human cell lines not infected with HTLV-1 essentially did not produce either of the TNFs. It was also found that the high production of TNF- by HTLV-1-infected cells partially correlated to their high sensitivity to human immunodeficiency virus (HIV) infection. Treatment of MT-4 cells, one of the most HIV-sensitive HTLV-1-infected cell lines, with antibody specific to TNF- reduced their sensitivity to HIV infection.     

An immunohistochemical study of protein kinase C distribution in fetal mouse vertebral column

Using polyclonal antibodies we have studied the distribution of protein kinase C in fetal mouse low thoracic vertebrae. By means of a pan protein kinase C antiserum recognizing the catalytic domain of the enzyme, we show that protein kinase C is markedly expressed in chondrocytes before birth. The enzyme seems to be very abundant in the more mature cells that are close to ossification centres as well as the periphery of the intervertebral disc, although it can also be detected in chondrocytes. In order to establish which protein kinase C isoenzyme(s) the chondrocytes produce, we employed polyclonal isoenzyme-specific antisera developed against three calcium-dependent isoforms (, , ) and three calcium-independent isoforms (gd, , ). Secondary antibody conjugated to alkaline phosphatase revealed that chondrocytes markedly express the -isoform. Cells were also weakly stained by the anti- serum. The immunostaining was completely abolished by pre-incubating primary antibodies with the peptide antigens to which they were raised. These results suggest that protein kinase C (and particularly the isoform) could play an important role in mouse fetal chondrogenesis of the vertebral column.     

The role of interoceptors in the regulation of oxygen saturation of arterial blood

Summary Studies were made of the oxygen saturation in arterial blood in animals during exposure to 7500 m in a chamber. The study was carried out after the photoelectrical method by means of continous oxyhemometry in rabbits and cats with denervation of carotid sinus zones, as well as in controls. In the controls the saturation diminished, to 55–62% and increased somewhat after 8–10 minutes' exposition to altitude. In the experimental animals the diminution of oxygen saturation was more pronounced, reaching 40–50% and remained within this range during the whole period of exposure.The experiments demonstrated that the dynamics and the degree of oxygen saturation of arterial blood in case of hypoxia depend on the function of the carotid sinus zones.Presented by Active Member of the Academy of Medical Sciences USSR V. N. Chernigovsky     

Treadmill exercise in dogs under β-adrenergic blockade: Adaptation of coronary and systemic hemodynamics

Summary The role of the -adrenergic system in the adaptation of cardiac output and coronary flow to exercise was investigated in 9 conscious dogs. Some of the experiments were carried out in dogs with experimental atrio-ventricular block and paced heart rates.-Adrenergic stimulation at rest and during exercise was modified by administration of the -adrenergic blocking agents Kö 1366 and propranolol. Submaximal treadmill exercise under -adrenergic blockade (-Bl) was tolerated with a decrease in cardiac output of 22.3±4.2%, in coronary flow of 25.2±6.0% and in mean arterial pressure of 8.2%.When heart rate was experimentally kept constant, results were qualitatively similar. In these experiments, in which the depressant effect of -Bl on heart rate could be eliminated, during exercise at identical heart rates a decrease of 26.1±4.3% in maximal rate of increase of aortic flow (an index of myocardial contractility) under -Bl was observed.Determinations of coronary sinus O₂-content revealed a fall in myocardial oxygen consumption (MVO₂) of 18.5±4.0% during exercise at 6 km/h under -Bl (Kö 1366).The results indicate that submaximal exercise can be tolerated with a diminished cardiac output, coronary flow and mean arterial pressure and with a definitely slowed adaptation response of these parameters. Despite diminished contractility, -Bl did not result in a change of MVO₂ per unit of external heart work (cardiac output x arterial pressure) under these conditions.Supported by Deutsche Forschungsgemeinschaft