Cyproheptadine blockade of a cardiogenic hypertensive chemoreflex.
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Animals↗
Biomedical subjects
F Urthaler
Publications and source records attributed to F Urthaler.
Comparison of the inotropic action of morphine and ketamine studied in canine cardiac muscle.
This study compares the inotropic action of morphine sulfate and ketamine hydrochloride on isolated canine right ventricular trabeculae. The heart was removed from 19 mongrel puppies weighing 5 to 9 kilograms and placed in Krebs-Ringer bicarbonate solution. The bathing solution contained 1.3 mM. of Ca2+ and was bubbled with a gas mixture of 95 per cent oxygen and 5 per cent carbon dioxide. At Lmax (i.e., the peak of isometric force-length curve) morphine even in large concentrations (up to 1 mg. per milliter) produced no significant direct inotropic effect. At the lower concentrations tested there was a minor but not significant increase in contractile performance, whereas at the highest concentration used there was a minor but not significant depression in contractility. In these same muscles lower concentrations of ketamine had a significant positive inotropic action, but a concentration of 200 mug per milliliter, which is approximately equimolecular to 1 mg. per milliliter of morphine sulfate, caused a profound depression in contractile performance. In the presence of a beta-blocking agent and in reserpine-pretreated muscles, low concentrations of ketamine, which had only a positive inotropic action in the normal muscles, now caused depression of contractile performance. The positive inotropic action of ketamine is thus indirect and mediated via adrenergic influences. At each concentration studied the direct inotropic action of ketamine was exclusively negative. Because of this bimodal inotropic action seen when adrenergic mechanisms are intact, we conclude that caution must be exercised when ketamine is given to patients previously treated or still under the influence of drugs having adrenolytic properties. Caution is also necessary when ketamine is used in patients having diminished cardiac adrenergic reserves as in congestive heart failure.
Animals↗
Comparison of contractile performance of canine atrial and ventricular muscles.
This study compared the contractile performance of a canine right atrial trabecula with that of a macroscopically indistinguishable trabecula isolated from the right ventricular apex. The heart was removed from nine mongrel puppies weighing 6-8 kg and placed in Krebs-Ringer's bicarbonate solution. The bathing solution contained only 1.25 mmoles of Ca2+ and was bubbled with a 95% O2-5% CO2 gas mixture. Each atrial trabecula was specially selected from the right atrial appendage. Histologically, these trabeculae showed a remarkable longitudinal orientation of the fibers. At Lmax (the length of the muscle at which developed tension was maximum) under identical conditions of temperature, rate of stimulation, ionic milieu, pH, and O2 and CO2 supply, right atrial trabeculae achieved the same developed and total tensions but in a much shorter time than did ventricular trabeculae. In both muscle groups the maximum developed tension averaged about 2.5 g/mm2. Since Lo (expressed as a fraction of Lmax) was less in atrial muscle than it was in ventribular muscle, we concluded that atrial muscle can be stretched considerably more than can ventricular muscle before optimum length is reached. At any given initial muscle length, the maximum of tension rise for atrial trabeculae amounted to at least twice that for ventricular trabeculae. At any given load up to 1.5 g/mm2, the maximum velocity of shortening of an atrial trabecula was about three to four times that of a ventricular trabecula. These results collectively indicate that the contractile performance of the right atrial muscle is in many respects superior to that of the right ventricle, at least under the conditions of these experiments.
Animals↗
Direct and vagally mediated chronotropic effects of morphine studied by selective perfusion of the sinus node of awake dogs.
Two milliliters of a morphine sulfate solution (1 mg/ml) perfused selectively into the sinus node artery of five trained unanesthetized dogs caused an immediate brief sinus tachycardia followed by a delayed but prolonged sinus bradycardia. Beta-receptor blockade was achieved by selective perfusion of propranolol hydrochloride solution (10 mug/ml) into the sinus node artery and did not prevent the initial sinus tachycardia. Selective perfusion of the sinus node with atropine sulfate solution (1 mug/ml), however, did prevent morphine from causing further sinus rate increase. The immediate positive chronotropic action of morphine was thus attributable to a peripherally located vagolytic action. The exact opposite was true with regard to the delayed bradycardia; it was due to a centrally mediated generalized increase in vagal tone regularly elicited by morphine.
Adrenergic beta-Antagonists↗
A comparison of His bundle electrograms recorded from the aortic root and from a plaque sutured near the His bundle.
For careful analysis of His bundle electrograms in the dog it is useful to have a stable rather than moving recording site. In this study we have compared the characteristics of His bundle electrograms recorded by two methods in each of ten anesthetized dogs. Records obtained with a Hoffman-type plaque electrode sutured in the vicinity of the His bundlewere not significantly different from ones obtained with a recording catheter wedged in the aortic root. In addition to measurements made during the resting state, comparisons also included those during selectively produced acute but transietn complete A-V block, sinus bradycardia, A-V junctional tachycardia, A-V junctional bradycardia, and various degrees of incomplete A-V block. A stable and accurate His bundle electrogram can be obtained from the aortic root and has the experimental advantage of not having to open the right atrium or place sutures near the A-V node of His bundle.
Acetylcholine↗
Fine structure of the conduction system and working myocardium in the little brown bat, Myotis lucifugus.
In the little brown bat, Myotis lucifugus, topography and ultrastructure of the sinus node and the atrioventricular (AV) node resemble those in large mammalian hearts, except that the P cells in the sinus node are smaller than those in the bat AV node or those in the sinus node of slower hearts (e.g., dog, man). Despite rich innervation in the bat nodes, true neuromuscular synapses are rarely formed. Bat working cardiocytes have a well developed sarcoplasmic reticulum, but otherwise resemble working myocytes of larger mammals.
Animals↗