摘要:

AbstractThe equation system earlier derived from the voltage clamp analysis on myelinated nerve fibres fromXeonpus laeviswas programmed for a digital computer. The response of the nerve model to linearly rising currents was computed for a number of quantitative modifications of the nerve model. The agreement between the computations and the earlier experimental results was qualitatively satisfactory. The quantitative agreement was not perfect but the discrepancies were not greater than what is expected from the known errors in the voltage clamp technique. The computations indicated that changes of any of the constants of the nerve model have effects on the rate of accommodation. The greatest effects were obtained by changing the inactivation of the sodium permeability. It was concluded, on the basis of the results obtained in the present and in the earlier investigation, that the slow excitability changes of the nerve fibres are well predicted by the equation system describing the ionic currents. Further, it was concluded that the normal variation in accommodation among myelinated nerve fibres fromXenopus laevisis accounted for mainly by variations in the rate constants ah although this may not be the only variable of importance. A variation in the turning on of the potassium permeability might also be significant.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04037.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe effect of cholesterol feeding on bile acid turnover and neutral fecal steroid excretion was studied in rabbits and human subjects. In rabbits the addition of 1% cholesterol to a low fat pellet diet (on the average 700 mg of cholesterol per day) caused a marked increase of the serum cholesterol level but a reduction of the turnover and the fecal elimination of deoxycholic acid. On the subsequent feeding of a semisynthetic cholesterol free diet, the serum cholesterol level decreased in spite of a further reduction of the fecal bile acid excretion. When human subjects received a diet containing egg yolk lipids, which provided 1.4 g cholesterol per day, the serum cholesterol level increased moderately over the control values, but there were no consistent effects on either the biliary bile acid composition or on the turnover of cholic acid. The amount of cholesterol excreted as neutral fecal steroids during the cholesterol feeding period corresponded on the average to 80 and 77% of the amount of cholesterol given to rabbits and human subjects respectively. Cholesterol and the plant sterolsβ‐sitosterol and methylcholesterol were metabolized into neutral compounds that were the same in rabbit and in human feces. Rabbit feces contained proportionally more 5α‐sterols than human

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04038.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe purpose of this investigation was to study the hydrostatic pressure changes within and outside the proximal tubules and to study possible changes in proximal cellular volume during the occlusion period following abruption of the renal blood flow and filtration. The pressures were measured directly using the micropuncture technique. The results demonstrate that the proximal tubular wall can resist a modest positive hydrostatic pressure from either the inside or the outside of the cellular wall for a short time interval. During reabsorption in the occlusion period a positive pressure seems to be created in the lumen of the proximal tubules probably due to “interfacial tension” and a positive luminal pressure is maintained until all the fluid has disappeared.The proximal cellular volume was estimated from the cellular area of cross‐sectioned proximal tubules of snap‐frozen kidneys. The area was measured by planimetry. It was demonstrated that the cellular area is the same (within about 10%) at the various rates of transcellular transport of sodium associated with spontaneous variations of the rate of glomerular filtration, and that it remains unchanged during the whole occlusion period. An increase of about 50% in the cellular volume occurred as soon as the luminal fluid was reabsorbed, i. e. about 20 sec after interruption of the renal circulation. The cellular volume then remained unchanged for several

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04039.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractPresynaptic depolarization of group I afferents produced by volleys in contralateral hind limb nerves has been investigated. It was found that a train of volleys in contralateral muscle or skin nerves did not alter the excitability of the Ia fibres or the size of the monosynaptic EPSP in motoneurones, i. e., there is no contralateral presynaptic inhibitory action onto group Ia fibres. A train of volleys in contralateral muscle and skin nerves increased the excitability of the contralateral Ib fibres to the flexors and extensors. The time course of the increased excitability had a latency of 10–30 msec, a slow rising phase, a late maximum at 50–80 msec, and a duration of about 150 msec. The crossed presynaptic actions originated from high threshold (group II and III) muscle afferent and cutaneous fibres. The results also indicate that Ib fibres may have a depolarizing action onto the contralateral Ib nerve termin

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04040.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe influence of rebreathing time when using a CO2rebreathing method for graphical determination of the mixed venous CO2tension was studied. An almost significant difference of 0.6 mm was found between values obtained at rebreathing rates of 30 and 50 breaths per min with rebreathing times of 22 and 13 sec. This should give a difference at rest of about 5 per cent when the cardiac output is calculated, with the higher value when the fast rate is used for the mixed venous CO2determination. The solubility of CO2in lung tissue probably doses not cause this difference.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04041.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractIn order to compare the effect of visceral and carotid sinus hypotension on the resistance vessels the peripheral resistance in 3 areas (hind body, kidneys and head) in the cat has been investigated by means of the constant perfusion rate technique during occlusion and desocclusion of visceral (coeliac, superior mesenteric and renal) arteries and of the carotid arteries. In all 3 areas clamping of the visceral arteries provoked a vasodilatation whereas a vasoconstriction in the hind body and kidney was observed during carotid artery occlusion. The clampings always produced significant rises in the general arterial blood pressure. The pressor response caused by visceral artery occlusion thus is produced in spite of a widespread dilatation of the resistance vessels—not as a consequence of a constriction in the same vessels. Denervation of the carotid sinuses plus section of the vago‐sympathetic trunks nearly always abolished the vasodilatation. Stabilising the blood pressure by means of a compensating device always abolished the vasodilatation during visceral artery occlusion. Under these circumstances the vasodilatation was not replaced by a vasoconstriction in the periphery. It has thus not been possible to demonstrate baroreceptor activity in the visceral arteries even under circumstances where the activity of the sino‐cardio‐aortic baroreceptor reflexes was eli

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04042.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractIn experiments on cats the heart rate response to occlusion of the visceral and carotid arteries has been investigated. Of 69 combined or separate occlusions of the coeliac and superior mesenteric arteries 6 produced a tachycardia, in 9 no change in heart rate occurred, in the rest a bradycardia occurred. Of 32 common carotid artery occlusions 2 produced a bradycardia, in 4 no change in heart rate was observed and in the rest a tachycardia was produced. The bradycardia during visceral artery occlusion is interpreted as a reflex elicited from the sinoaortic baroreceptors and caused by the rise in blood pressure. It is further observed that the pressure increments caused by visceral artery occlusion have a maximum at subnormal systemic pressures (between about 65 and 100 mm Hg). This is contrary to the blood pressure rise caused by carotid artery occlusion which as a rule is greater the greater the systemic pressure, in accordance with the threshold concept for the baroreceptors.Therefore, at low systemic pressures (below about 110 mm Hg) a higher response to combined occlusion of the coeliac and superior mesenteric arteries than to carotid artery occlusion is the rule, the opposite is the case at higher systemic pressures.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04043.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe time response pattern of nicotine and the nicotine analogue 3‐pyrrolidino‐methylpyridine (W‐16) on the noradrenaline (NA) content of heart, spleen, kidney and liver was studied following intraperitoneal administration in rats. It was found that both compounds produced a transient but significant decrease. Nicotine produced an effect that was visible within 5 min with the NA content returning to control levels in 60–180 min. Although quantitatively different, W‐16 produced an effect qualitatively similar to nicotine. The effect of nicotine and several nicotine analogues on the 24‐hour urinary excretion of catecholamines was also studied in rats. Three out of four analogues investigated produced a slight increase in the excretion of adrenaline (A) and NA at high dose levels (5–10 mg/kg). At a dose of 1 mg/kg, nicotine produced a significant increase in the 24 hour urinary excretion of

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04044.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe energy cost of walking up and down a A‐shaped, 1 m high staircase was studied in 10 male and 10 female subjects in terms of the O2requirement for performing the work under truly aerobic conditions. Two different speeds of walking were used, yielding external work loads ofk× 14.7 andk× 26.7 kpm/min (k= body weight of individual in kg) in both the positive and negative phases. At the lower speed the net O2cost per kg b. w. averaged 16.8 ml/min, independent of sex; at the higher speed the corresponding value was 33.0 ml/min in the men, and 32.0 ml/min in the women. From these values the average physiological load was estimated tok× 8.2 kpm/min for men and women at the lower speed, and tok× 16.2 andk× 15.7 kpm/min for men and women, respectively, at the higher speed. The ratio of O2costs for the positive and negative works approximated 8: 1 at the lower speed, and 5: 1 at the higher speed. During each period of positive work the calculated O2demand of a 70 kg man exceeded the O2supply to the working muscles by about 60 ml at both speeds. This O2debt of 60 ml could be contracted without any increment in the lactacid O2debt and supports the notion that a certain amount of O2can be released from the myoglobin O2store before anaerobic processes become involved. The O2capacity of this aerobic debt mechanism was calculated to be in the order of 3 ml per kg of active muscle tissue. Evidence is presented that, in the steady state, the upper limit for performing work under truly aerobic conditions corresponds to about 70 per cent of the maximal O2consu

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04045.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

AbstractThe effects of i. a. infused ACh, ATP, histamine and bradykinin (and kallidin) were studied on the isolated calf muscle preparation of cats and compared with the vascular response to graded exercise elicited by stimulating the sciatic nerve. With a plethysmographic technique the effects on the resistance vessels, the capillary filtration coefficient (CFC) and the capacitance vessels were assessed and through a more indirect approach the occurrence of an increased capillary permeability was estimated. All procedures decreased flow resistance. ACh and ATP increased CFC approximately as much as exercise and, like exercise, without any signs of increased capillary permeability. As a contrast bradykinin and particularly histamine produced higher CFC values at every degree of diminished flow resistance, together with other signs of increased capillary permeability. The increased permeability vanished as rapidly as the vasodilator response after infusion. ACh and ATP dilated the capacitance vessels but bradykinin, histamine and exercise did not. It is concluded: 1) that all procedures studied increase nutritional blood flow, 2) that bradykinin and histamine produce a promptly reversible increase of capillary permeability in the same doses that are needed for dilatation and 3) that none of the substances when infused i. a. could exactly reproduce the vascular response of exercise.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1965.tb04046.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY