Showing papers in "American Journal of Physiology in 1938"

Electrocardiographic changes and concentration of potassium in serum following intravenous injection of potassium chloride

Abstract: In mammals the intravenous injection of a solution of potassium chloride may produce either a sequence consisting of extrasystoles, tachycardia and finally ventricular fibrillation, or on the other hand cardiac arrest without arrythmia (5, 7, 8). Recently Nahum and Hoff (6) found in the rabbit that fibrillation was produced by the rapid injection of a concentrated solution of potassium chloride, while arrest without arrythmia occurred following slow injection of an isotonic solution. Arrest produced in this fashion is preceded by a definite sequence of electrocardiographic changes. The present studies were undertaken to determine what relationship, if any, exists between the concentration of potassium in the serum and the various electrocardiographic changes observed following intravenous injection of an isotonic solution of potassium chloride. PROCEDURE. Four dogs weighing from 15 to 20 kilos were employed in five experiments. Morphine sulphate, 10 mgm. per kgm. body weight, was injected subcutaneously thirty minutes before each experiment. A control electrocardiogram was obtained from lead II, and an initial sample of venous blood withdrawn under oil from the jugular or femoral vein. In three experiments (1, 2, 4 of table 1) an isotonic solution of potassium chloride (1.12 per cent) was then injected into the femoral vein at a rate approximating 10 cc. per minute, until the death of the animal. In one experiment (exp. 3 in table 1) injection was discontinued before cardiac arrest had occurred, and the animal allowed to recover. The same animal received at a later date an injection of an eight times isotonic solution of potassium chloride (exp. 5, table 1) which was continued until death occurred.

The mechanism of regulation of the blood sugar by the liver

Abstract: That the liver is essential for the maintenance of the level of blood sugar was demonstrated adequately by the early studies on the dehepatizeil animal. Because of the complexity of the problem, there has been much speculation concerning the mechanism responsible for the normal constancy of the blood sugar level and for the dextrose tolerance curve after the administration of sugar. From the studies of Soskin and his co-workers (1, 2, 3, 4, 5) on the dextrose tolerance curve under various experimental conditions, it would appear that whenever the blood sugar tends to rise above the normal level, the liver responds by diminishing its output of sugar to the blood. The stimulus which elicits this hepatic inhibitory response is the blood sugar itself, and the threshold of stimulation of the hepatic mechanism in a particular animal coincides with the level of blood sugar which that animal habitually maintains. It is suggested that this mechanism is chiefly responsible for the characteristic dextrose tolerance curve when sugar is administered to the normal animal. The influx of exogenous sugar into the blood stream raises the level of the blood sugar above the threshold of stimulation of the homeostatic mechanism. The liver promptly curtails the supply of sugar which it has been pouring into the blood. the liver. The exogenous sugar thus temporarily replaces the supply from Utilization and storage rapidly return the blood sugar toward its normal level, whereupon the liver resumes its secretion of sugar. This conception was based on indirect evidence. The facilities of the Institute of Experimental Medicine of The Mayo Clinic made it possible to obtain direct proof of the operation of this homeostatic mechanism of the . . liver. METHODS. From one to four months prior to our experiments, a twostage ligation of the posterior vena cava, just below the liver, was performed on the dogs to be used. This rerouting of the blood from the caudal

The renal tubular reabsorption of glucose in the normal dog

Abstract: It is known that glucose is filtered through the glomerulus in the same concentration as it is present in the water of the plasma (Walker and Reisinger, 1933), and that, its absence from the urine at normal plasma concentrations is due to the circumstance that it is reabsorbed by the tubule. In the amphibian kidney, this reabsorption is effected by the proximal segment (Walker and Hudson, 1937). In mammals the reabsorptive proces is never complete, a small amount of glucose being present in the urine at normal plasma glucose levels (Harding, Nicholson and Archibald, 1936). Frank glycuresis at elevated plasma glucose levels is due, not to the complete cessation of reabsorption, but to the fact that more glucose is filtered than can be reabsorbed (Ni and Rehberg, 1930). Ni and Rehberg (1930) have given a quantitative description of the reabsorption process t but we believe that their data are unsuitable for this purpose because veno us blood was used for the calculation of the rate of glucose filtration in their experiments, because there were marked variations in the rate of filtration, and because significant errors were introduced by very rapidly changing plasma glucose concentrations. The present observations, also directed towards a quantitative description of the reabsorptive process, have been made in su .ch a manner as to eliminate these sources of error. EXPERIMENTAL PROCEDURE. Observations have been made upon two normal, well trained female dogs which were loosely restrained upon a comfortable animal board, and upon four dogs decerebrated under ether and chloroform anesthesia some hours prior to their use. Constant creatinine and varying glucose concentrations in the plasma were obtained by means of constant intravenous infusions. Urine collections were made by an inlying catheter, and at the end of each period the bladder was emptied as completely as possible and washed with warm water, this wash fluid being added to the urine prior to the final dilution for analysis. In the decerebrate dogs the ureter was cannulated and the urine delivered directly into a collecting vessel through a glass tube of small volume.

Experimental evidence supporting the conception of "adaptation energy"

Abstract: It has been shown that when an organism is exposed to a stimulus to the quality or intensity of which it is not adapted, it responds with a reaction which has been termed the “general adaptation syndrome” (Selye, 1936a, 1937a, 1938a). The symptoms of this syndrome have been described elsewhere (Harlow and Selye, 1937; Howlett and Browne, 1937; Karady et al., 1938; Schacher et al., 1937; Selye, 1936b, 1937b, 1937c; Selye et al., 1936). They are largely independent of the specific nature of the agent to which adaptation occurs, so that the reaction has been regarded as the somatic expression of damage as such. The general adaptation syndrome develops in three distinct stages which have been termed: 1, the stage of the alarm reaction; 2, the stage of resistance, and 3, the stage of exhaustion. The symptoms of the alarm reaction, among which thymus atrophy and adrenal hyperplasia are particularly conspicuous, disappear during the stage of resistance in spite of continued treatment with a uniform damaging stimulus (a drug, exposure to cold, excessive muscular exercise, etc.) but these same symptoms reappear during the so-called stage of exhaustion and finally death ensues. A similar three stage reaction was recently observed by Giragossintx and Sundstroem (1937) in rats kept under low oxygen tension. In these experiments, the loss of acquired adaptation during the stage of exhaustion is difficult to explain but as a working hypothesis, it was assumed that every organism possesses a certain limited amount of “adaptation energy” and once this is consumed, the performance of adaptive processes is no longer possible (Selye, 1938c). Previous observations (Karady et al., 1938; Selye, 1938a, 193813) showed that during the alarm reaction, the resistance of the organism is increased, not only to the stimulus with which the alarm reaction had been elicited but also to agents of a different nature. However during the second stage of the adaptation syndrome, this non-specific resistance vanishes rapidly at a time when the specific resistance to the agent with which the animal had been pretreated, is still very high. These findings

The effect of body temperature on reaction time

Abstract: Diurnal variability in mental, motor and sensory performance has been studied by many investigators. The variability in conclusions is as numerous. Curves have been described with a, continuous rise; b, continuous fall; c, morning rise, afternoon fall; d, morning fall, afternoon rise; e, no curve whatsoever, and various curves with several notches. In 1906 Marsh (1) published an extensive study in which he reported instances of each of these types of curves. More recently, Freeman and Howland (Z), in a review of the literature, list many examples of each type of curve. None of these many workers, however, made any observations of body temperature at the time of testing the subjects prior to Kleitman (3) who published diurnal curves with morning rises and afternoon falls for speed and accuracy of a variety of tasks, such as dealing cards, code transcription, multiplication, mirror drawing, as well as the curve for temperature observed at the time of the tests. Increase in temperature appeared to improve performance markedly. The present study was designed to investigate the possible diurnal character of rather simple performances, likewise in relation to body temperature. It was also desired to compare the influence of temperature fluctuations on simple tasks with their influence on more complicated tasks. The performances selected for this purpose were purely sensorymotor: reaction to light and reaction to sound, and sensory-mental-motor: choice reactions to light and sound. METHODS. The time required to react to visual and auditory stimuli was studied. Five subjects, male graduate students and an instructor, participated, each acting alternately as subject and observer. The tests were made at various times of the day: at 9 a.m., 11 a.m., 1 p.m., 3 p.m., 5 p.m., 7 p.m. and 9 p.m., except for one subject (N.B.) who was tested at 7 a.m., 9 a.m., 11:30 a.m., 6 p.m. and 11 p.m. and one subject (N.K.) who was tested at 9 a.m., 11 a.m., 3 p.m., 5 p.m. and 9 p.m. A complete test consisted of twenty trials each for a, simple reaction: to white light; b, simple reaction : to sound of a telegraph key; c, choice reaction : response to

Properties of mammalian nerve fibers of slowest conduction

Abstract: The present studies of mammalian C fibers were undertaken in order to define more precisely the constants of these fibers and to extend our information about the aspects of their behavior during activity which have not previously been investigated systematically. All the experiments have been designed with the end in view of learning how the behavior takes place under physiological conditions. Unless special precautions are taken, the manifestat*ions of activity in preparations of isolated nerve may differ widely from what may be expected in the body, particularly with respect to the after-potentials and tlhe excitability cycle. Exact information about the last mentioned features of activity is particularly essential, as an understanding of the properties of the axon, as a sample of the properties of other parts of the neuron, is fundamental to an understanding of the excitation of the neuron at the synapses with preganglionic fibers in autonomic ganglia. METHODS. The most important consideration when isolated nerves are the subjects of observation is the employment of fresh preparations and the restriction of stimulation to a minimum, as the effects of conditioning are cumulative and long-lasting. Drying is the most troublesome technical difficulty. In order to obviate it, the new nerve chambers have been equipped with a bath into which the nerve may be immersed without opening the box. Krebs’ solution in equilibrium with 5 per cent CO2 and 95 per cent 02 was used routinely, because of the demonstration by Lehmann (1937) of the importance of maintaining A fibers at a normal and constant pH. Actually, as will be seen later, the precaution is of much less importance for C fibers, as their sensitivity to changes in reaction is low. The only test of whether a nerve is being studied under physiological conditions is to compare it with a like nerve under its normal perfusion of blood in the body. Accordingly the method used by Gasser and Grundfest (1936) for mammalian A fibers was employed. It depends upon the parallelism between the after-potential and the excitability cycle. Potential and excitability are recorded from the excised nerve, and ex-