Showing papers in "American Journal of Physiology in 1954"

Cerebral blood flow and cerebral oxygen consumption during hypothermia.

Abstract: C URRENTLY there is widespread interest in the physiologic effects of cold, and in the use of hypothermia with surgery (I, 2). Although no gross neurologic derangements have been observed following the application of this technique in man and experimental animals (3, 4), it seemed appropriate that a special study be made of the effects of hypothermia on cerebral physiology. Cerebral blood flow, cerebral oxygen consumption, cerebral vascular resistance, as well as systemic blood pressure and pulse rate were investigated.

Exercise, Food Intake and Body Weight in Normal Rats and Genetically Obese Adult Mice

Abstract: I T IS GENERALLY assumed that the relationship of food intake to exercise is one of direct proportionality above the basal level corresponding to inactivity. It is the purpose of the first part of this article to show that such a concept is an oversimplification at variance with the facts. Similarly, it is usually assumed that following exercise an obese animal or person will increase food intake in direct proportion, whatever the intake prior to exercise or the energy expended in exercise. It has been shown (I) that in the hereditary obese hyperglycemic syndrome (2, 3), a decrease in voluntary activity (to less than 2 % of the normal in adult animals) is an essential aspect of the etiology of the obesity; this lack of activity was shown to precede the development of the obesity and is not simply a result of the overweight (I). When obese mice also carry the waltzing gene and are in nearly constant rotary movement in their cages, their weight rarely exceeds 40 gm instead of twice that value. In another report (4) it has been demonstrated that mice made obese by goldthioglucose injection (2) will lose weight if given the opportunity to practice unrestricted exercise. It is the purpose of the second part of this paper to show that the development of hereditary obesity in mice can be considerably slowed down by forcing these animals to exercise.

Excretion of Sodium, Potassium, Chloride and Carbon Dioxide in Human Parotid Saliva

Abstract: H EIDENHAIN (I) first demonstrated that the concentration of inorganic salts in the submaxillary saliva of dogs varies in proportion to the secretory rate. Gregersen and Ingalls (2) showed that the concentration of sodium increases with increasing rates of secretion, whereas the concentration of potassium is independent of salivary flow. This finding has been confirmed by later investigators working on submaxillary saliva of various animals (3-5) and on human mixed saliva (6). In the present experiments the concentrations of sodium, potassium, bicarbonate, and chloride were measured simultaneously in human parotid saliva following stimulation of the secretion by the subcutaneous injection of beta-methyl-acetylcholine hydrochloride. The results obtained on the relative rates of excretion of potassium and sodium by the parotid gland are compatible with the hypothesis that both cations are brought into a precursor solution at a rate which varies in direct proportion to the rate of salivary flow, and that sodium is withdrawn from this precursor solution by a process of reabsorption which is limited by a maximal capacity.

Mean circulatory filling pressure measured immediately after cessation of heart pumping.

Abstract: W HEN the heart stops, the arterial pressure falls and the venous pressure rises until aftes 30-50 seconds the two pressures almost reach equilibrium. This equilibrium pressure, which presumably is equal to the pressure in all portions of the circulatory system, has in previous studies from this laboratory (1-3) and in this present study been called the ‘mean circulatory filling pressure.’ The term ‘mean systemic pressure’ as used by Starling (4) has not been used because the word ‘systemic’ now has the connotation of applying to the peripheral circulatory system alone rather than the entire circulatory system. Also, the terms ‘hydrostatic mean pressure’ as used by Bolton (5) and ‘static blood pressure’ as used by Starr (6) have not been employed in this discussion because to many physiologists the word ‘static’ means ‘unchanging’ and it has been shown many times that the autonomic reflexes continue to cause marked changes in pressures throughout the circulatory system even after the heart stops pumping (1-7). Another reason for using the term ‘mean circulatory filling pressure’ is that, even though the pressures throughout the circulatory system under dynamic conditions are widely variant, there is a mean integrated pressure in the circulatory system all of the time, If one takes into consideration the different elasticity coefficients of the different blood vessels and also takes into consideration the different volumes of the different beds, then the mean integrated pressure of the circulatory system at any given instant can be shown mathematically to be exactly equal to the mean circulatory filling pressure should the heart stop _~~ ____Received for publication May IO, I#+ 1 This investigation was supported by a research grant from the National Heart Institute, Public Health Service. 2 Student Fellow, National Foundation for Infantile Paralysis. beating and all pressures come to equilibrium instantaneously. Therefore, use of a term which implies that there is a continuously present mean pressure in the circulatory system has many advantages in emphasizing the importance of this pressure. The mean circulatory filling pressure as it exists in the body at any given instant cannot possibly be measured because life is dependent on dynamic circulatory conditions. On the other hand, it has been pointed out by all investigators who have measured the mean circulatory filling pressure that shortly after the heart stops beating, intense vasoconstriction begins throughout the circulatory system (4, 6, 7). Consequently, in order to estimate accurately the mean circulatory filling pressure as it exists at any given moment, it is essential that measurement of this value be made within a few seconds after the heart stops beating or, in other words, before significant changes in vasomotor tone can take place as a result of reflexes. In order to make such rapid measurements it is necessary to establish rapidly equilibrium of the circulatory pressures by artificial means, for the rate of blood flow from the arteries to the veins is too slight for rapid equilibrium to occur. Except for the preliminary measurements reported from this laboratory (1-3, 7), the mean circulatory filling pressure has never been determined within the short interval of time after the heart stops beating and before reflex vasomotor constriction begins. In the present study, attempts which are believed to have been successful have been made to make such measurements under a number of different conditions.

Transcapillary pulmonary exchange of water in the dog.

Abstract: T HE CAPILLARIES in the lungs, in contrast to capillaries elsewhere in the body, are in effect bathed in air rather than water. There is little histological evidence for a substantial pulmonary interstitial space; instead, the bulk of the lung tissue appears to consist of cells and blood vessels. Perhaps because of these anatomical peculiarities little or no consideration appears to have been given to the possibility that large amounts of water might exchange across the walls of these capillaries. The data presented below, which are part of a more general study of capillary permeability, suggest that, in the normal dog, water does cross these capillaries in amounts per unit time which approach in magnitude the pulmonary blood flow.

Imperfect homeothermia in the hereditary obese-hyperglycemic syndrome of mice.

Abstract: T HE GENERAL TRAITS of a Mendelianrecessive syndrome charac terised by h obesity, hyperglycemia (either spontaneous, or immediately elicited by growth hormone or high protein diets), atrophic changes and ulceration of the skin, hypertrophy of the islets of Langerhans and by other metabolic, nutritional, and endocrine disturbances, have already been described in two general reviews (I, 2). It has since been shown that the animals show hypercholesterolemia (3) and that the increased lipogenesis from acetate is particularly marked in young animals even under paired-fed and constant weight conditions (4). A probable etiology involving primary hypersecretion of pancreatic hyperglycemic factor with a secondary hypersecretion of insulin has also received experimental support (2, 5). In a previous report on the effect of cold on this type of obese animals (6), it was shown that they are extremely sensitive to cold and die in a few hours when exposed to an environmental temperature which their non-obese siblings withstand indefinitely. It was demonstrated that the sensitivity to cold was only partially corrected by certain thermogenic agents and, if anything, enhanced by cortisone and ACTH. When the results were discussed, it was pointed out that this lack of resistance can represent a priori either a failure of the mechanism regulating heat loss or a failure of the mechanisms responsible for heat production. It was further pointed out

Rostral projection pathway of the vestibular system.

Abstract: : Electrical stimulation of the vestibular nerve excited neural activity which was tracked to the cerebral cortex in the cat Recordings from the vestibular nuclei, midbrain, thalamus, and cortex revealed that cortical projection is achieved through second-order neurons which decussate in the region of the trapezoid, lie in a position between the lateral and medial lemnisci, and end in the thalamus near the boundaries of the medial geniculate body and the posterolateral ventral nucleus Third-order neurons then project to the posterior bank of the anterior suprasylvian gyrus The route of projection appeared to consist of a group of small and diffuse fibers which were difficult to identify

Effect of Cholesterol Vehicle in Experimental Atherosclerosis

Abstract: ginmming of timis cemmtmmrythat cholesterol feeding of rabbits led to atimeronmata, a large ntmmber of chmolesterol-feed!ing experiments have been carried oumt. In these experiments timis sterol was usually administered! in an oil (fat) suspension, but comparison of different types of fat was not cairied out. About 15 years ago we began to compare the effect of the cholesterol vehicle upon cisolesterol-induced atherosclerosis. In the first of these experiments, cholesterol was ad!dedl dlirectly to time rabbit chow or was fed together with a partially saturated fat (vegetable shortening; iodine value, 72) or a hmighmly unsaturated fat (cormm oil; iodine value, 130). We observed that the diet containing cholesterol plus corn oil was considerably less atherogenic tlman that containing shortening (1). Time shortening cholesterol regimen was slightly less atheu-ogenic tisan was tise dhet containing no fat. A second! experiment showed that time degree of saturation of time fat did indeed! play a role in cholesterol-indumced atherosclerosis in rabbits. A diet containing cholesterol and methyl stearate (iodine value, 0) was more athmerogenic than one containing methyl oleate (iodine value, 90) and this diet was, in turn, more atimerogenic

Ultracentrifugal studies of high density serum lipoproteins in clinically healthy adults.

Abstract: INDGREN and co-workers (I) have described L the properties and methodology for the ultracentrifugal study of the entire spectrum of lipoproteins present in human serum. The three most dense lipoproteins described by Lindgren et al. represent the subject of present considerations. These lipoproteins have been identified by their estimated hydrated densities as a lipoprotein of density 1.05 gm/ml, a lipoprotein of density 1.075 gm/ml, and a lipoprotein of I.145 gm/ml. At present the precise interrelationship of the chemically isolated alpha lipoproteiins described by Oncley et al. (2) to these three ultracentrifugally defined high density lipoproteins is not completely clear. Since the exact relationship to chemically isolated alpha lipoproteins remains indeterminate we have avoided the designation of the three high density lipoproteins as alpha lipoproteins and instead have utilized the following nomenclature: the lipoprotein of hydrated density 1.05 gm/ml = HDL12; the lipoprotein of hydrated density 1.075 gm/ml = HDL2; the lipoprotein of hydrated density 1.145 gm/ml = HDL3. The role of the low density lipoproteins (of hydrated density less than 1.04 gm/ml) in the systematics of serum lipid transport have been -Received for publication May -3, 1954. l This work was supported in part by the National Heart Institute, Public Health Service, The Atomic Energy Commission and the Life Insurance Medical Research Fund. 2 The designation HDL is used to indicate the high density lipoproteins for contrast with the low density group of lipoproteins for which the component of highest hydrated density is 1.04 gm/ml. The cutoff 1.04 gm/ml is arbitrary. Reference to HDLl, HDL2 or HDLS lipoprotein does not infer that a single discrete lipoprotein at each density is necessarily involved. The homogeneity or lack thereof of such lipoproteins deserves further investigation. described (3-5). Ultimate further understanding of lipid transport requires similar knowledge three of the population distributions of the high density lipoproteins and of their interrelationships with the low density group of lipoproteins. The high density lipoprotein determinations described below were made on 566 randomly chosen clinically healthy adults of both sexes, between the ages of 18 and 69 years of age.

Electrical activity of skeletal muscle of normal and acclimatized rats on exposure to cold.

Abstract: T HE PRINCIPAL ALTERATION in heat balance which occurs in rats exposed to a moderately cold environment is characterized bY an increased produ ction of heat, rather than by a decrease in its loss. This has been demonstrated by the measurement of oxygen consumption, and by direct calorimetry (1-3). Increased oxygen consumption in the cold can be attributed to increased activity of skeletal muscle and also, in the acclimatized rat, to an increase in the metabolic activity of visceral tissues (4). On initial exposure, the non-acclimatized rat is able to increase its oxygen consumption to almost as high a level as that of the acclimatized animal, but under severe conditions lacks the same capability to continue producing heat at the high rate necessary to maintain the temperature of the body (5). In addition to the altered metabolism of visceral tissues already demonstrated, a difference between the acclimatized and nonacclimatized rat might also exist in the responses of the skeletal muscles to cold. Experiments were carried out in order to measure the electrical activity of the skeletal muscle of acclimatized and non-acclimatized rats and to relate these find ings to the rate of oxygen consump tion and to body tempera ture at normal and low ambient temperatures.

Total water content of laboratory animals with special reference to volume of fluid within the lumen of the gastrointestinal tract.

Abstract: I N RECENT YEARS, there has been much progress in the study of body water and its sub-divisions, and yet, little attention has been given to fluid within the lumen of the gut and its possible significance in body water measurements. The very facts that, a) flow of water across the gut-wall is bi-directional (I), b) that labeled water placed within the gut rapidly reaches equilibrium with other body fluids (2), G) that labeled water in jetted intravenously rapidly reaches an equilibrium in gut fluid (3), and d) that feces contain the same concentration of tagged water as other body fluids at equilibrium (4), suggest that fluid in the gut should be considered, unless of course the amount of this water is so small as to be of no significance. Should, however, gut fluid be of significant volume, then some of our present day in vivo measurements are yielding results which are being incorrectly interpreted, because certain measuring agents enter into the gut while others do not. For example, heavy water and sucrose or inulin have been utilized simultaneously to determine total body water and extracellular fluid, the difference between the two being considered as water within cells. Heavy water enters the &t lumen and hence includes in its volume distribution whatever water may be contained within the gut. On the other hand, neither inulin nor sucrose injected intravenously enter the gut fluids (5, 6). Thus, if body water is partitioned by simple subtraction, the result is an underestimated extracellular fluid volume while the intracellular phase is overestimated by the amount of fluid located within the gut. Since no known study has been made of gut fluid in relation to the subject of body water, it was thought appropriate to investi-

Active cellular transport of urea by frog renal tubules.

Abstract: P KEVIOUS studies have shown that, in the frog, urea is excreted in part by tubular activity. Marshall and Crane in their classic paper on the secretory function of renal tubules (I) emphasized that urea excretion in frogs differed from that in mammals and resembled phenol red elimination in frogs and mammals in that its excretory efficiency (U/P ratio) was depressed as plasma concentrations were raised. This was interpreted as indicating a saturation of the secretory cells. They concluded that this secretory activity was confined to the proximal convoluted tubules because both urea and phenol red were found to be more concentrated in the dorsal part of the frog’s kidney, which contains the proximal segments, than in the ventral. Later JMarshall showed that urea concentrations in urine may exceed those simultaneously in plasma by as much as zo-3+fold, whereas xilose, only slightly reabsorbed, had U/P ratios which never exceeded 3.0 (2). Walker and Hudson showed in tubular puncture studies that, in contrast to Necturus, the frog concentrates urea to a degree greatly exceeding that of glucose in phlorizinized animals. They concurred with Marshall that some urea is excreted by tubular activity (3). SchmidtNielsen and Forster found that urea clearances were 4-110 times higher than simultaneous glomerular filtration rates in bullfrogs. p-Aminohippurate (PAH) clearances, which measured renal plasma flows, were approximately three times higher than simultaneous urea clearances (4, 5). The studies reported here were undertaken to determine to what extent the urea excretory process exhibits those characteristics previously demonstrated for PAH and phenol red transport by renal tubules, namely, a well-defined maximal rate, dependence upon