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Biomedical subjects

J Mason

Publications and source records attributed to J Mason.

At least 289 records · Page 16Linked to original sources
PubMed1978

The early phase of experimental acute renal failure. III. Tubologlomerular feedback.

Experiments were designed to determine whether tubologlomerular feedback, which modifies nephron filtration rate in response to alterations in the macula densa sodium chloride concentration, was still apparent in the initiation phase of various types of acute renal failure. The response of the glomerulus to changes in the macula densa stimulus was evaluated in haeme pigment, ischaemic and nephrotoxic induced renal damage by measuring early proximal flow rates. The sodium chloride concentration at the macula densa was varied between low values and isotonicity in two ways: firstly, by interruption of flow through the loop of Henle, followed by orthograde perfusion with Ringer's solution; secondly, by retrograde perfusion of the loop of Henle with isosmotic mannitol or Ringer's solution. In all nephrons examined, filtration rate was inversely correlated to the macula densa sodium chloride concentration, except during orthograde perfusion with 10(-4) M furosemide in Ringer's solution, when, despite the high sodium chloride concentration, filtration rate remained high. It is concluded that the mechanism of tubuloglomerular feedback is viable after the onset of compromised renal function, and may, as postulated, account for the reduction in blood flow and nephron filtration rate occurring in acute renal failure.

Acute Kidney Injury↗
PubMed1978

The role of sulphide and sulphide oxidation in the copper molybdenum antagonism in rats and guinea pigs.

The sulphide metabolism of rats fed molybdate up to levels of 1000 ppm molybdenum was examined and large decreases in hepatic sulphite oxidase activity observed; overall sulphide oxidation capacity was also reduced. Molybdate but not tungstate caused increases in the total plasma copper of guinea pigs but in particular the appearance of a new TCA-insoluble fraction. The effect was increased by the addition of 500 ppm sulphur as sulphide, to the molybdate diet whereas the addition of 500 ppm S as sulphate was ineffective. 100 ppm Mo was less effective as thiomolybdate (MoS4=) than as molybdate. The significance of these results in relation to the role of sulphide in the Cu-Mo-S interaction is discussed.

Animals↗
PubMed1978

The influence of dietary sulphur, molybdate and copper on the absorption, excretion and plasma fraction levels of 99Mo in sheep.

The effect of increased dietary sulphur, copper and molybdate on the metabolism of 99Mo administered via the rumen or duodenum was examined. Duodenally administered 99MoO4= was efficiently and rapidly absorbed and excreted via the urine; dietary modifications did not alter this pattern although increased dietary S increased the excretion rate. The passge of 99MoO4= through the rumen led to chemical modification, so that, particularly at high S levels, most of the radioactivity remained in the feces; increased dietary Mo led to increased absorption whereas increased copper decreased absorption. Incorportion of radioactivity into the TCA insoluble plasma fraction was shown with increased dietary S and particularly when both dietary S and Mo were increased. The compatiblity of the results with the hypothesis of ruminal thiomolybdate formation and subsequent reaction with dietary or tissue copper is discussed.

Animals↗
PubMed1977

The early phase of experimental acute renal failure. I. Intratubular pressure and obstruction.

Tubular obstruction in acute renal failure, postulated to cause the restricted excretory function, is suggested by raising intratubular pressure, to lower effective filtration pressure and diminish urine output. To examine the applicability of the obstruction hypothesis to the pathogenesis of experimental acute renal failure, proximal intratubular pressure and renal function were measured after renal insults of different origins and severity. Obstruction in acute renal failure kidneys should manifest itself as an increase in intratubular pressure for a least 12 h, for within this time period following ureteral occlusion, elevated pressures were found to reflect obstruction. The consistent existence of raised proximal intratubular pressure in acute renal failure kidneys could not be detected; ischaemic and nephrototoxic models were found in which no rise in intratubular pressure could be demonstrated. The oliguric nature of acute renal failure kidneys could not be verified; ischaemic and nephrotoxic models were found in which urine output was either normal or enhanced. Only for methaemoglobin induced renal failure were raised intratubular pressure, oliguria and casts concurrent. It is concluded that obstruction is not a consistent feature of experimental acute renal failure and that the obstruction hypothesis may be specifically applicable to only a few models, which include haeme pigment and folic acid induced renal failure.

Acute Kidney Injury↗
PubMed1977

The early phase of experimental acute renal failure. II. tubular leakage and the reliability of glomerular markers.

Experiments were designed to determine whether leakage of substances across the tubular epithelium, which are impermeant in the normal kidney, falsifies the measurement of glomerular filtration rate in acute renal failure. Permeability to those substances most commonly used for filtration rate determination, polyfructosan, inulin and ferrocyanide, was estimated by measuring their recoveries following perfusion through various nephron segments in haeme pigment, ischaemic and nephrotoxic models of acute renal failure. Late proximal recovery of 14C ferrocyanide was only marginally decreased compared to controls, by a maximum of 6%. Distal recovery of polyfructosan, 14C and 3H inulin were depressed somewhat more, by a maximum of 11%. Urinary recovery of 14C inulin was reduced by only 15% in kidneys showing severely restricted renal function. It is concluded that tubular leakage is not a feature of significance in the early phase of moderate acute renal failure, that ferrocyanide and inulin are reliable markers for the determination of nephron filtration rate and water reabsorption, and that the reduction in whole kidney inulin or polyfructosan clearance reflects primarily a reduction in glomerular filtration rate.

Acute Kidney Injury↗
PubMed1977

The echocardiophone: a new means for observing spatial movement of the heart.

The paper describes a new pocket size instrument called the "Cardiophone" for the diagnosis of cardiac dysfunction. It is a continuous wave swept frequency ultrasonic echo-location system which produces dynamic auditory signals corresponding to the positional change of internal structures of the heart. The four valves are relatively easy to locate compared with conventional ECG machines. Preliminary clinical evaluation results are presented indicating the potential of the instrument for the general practitioner.

Echocardiography↗
PubMed1977

Successful retransplantation of the human heart.

Cardiac retransplantation has been performed in five patients at Stanford University Medical Center. Long-term survival and rehabilitation have been achieved in two cases. In the first case retransplantation was performed 57 days after the initial procedure because of persistent acute graft rejection. The second patient underwent retransplantation 27 months postoperatively because of documented accelerated graft atherosclerosis. The major indications for cardiac retransplantation consist of intractable acute rejection and late postoperative graft atherosclerosis. These complications should prompt consideration of cardiac retransplantation in carefully selected cases.

Adolescent↗
PubMed1977

Malaria field studies in a high-incidence coastal area of El Salvador, C.A.

A three-year investigation was made of the incidence patterns and characteristics of malaria in a small high-incidence coastal area of El Salvador with a resident population of about 6,000 persons and a migrant population of 3,000 to 4,000 others. It found a significant increase in the incidence of Plasmodium falciparum cases during the three-year period, combined with relative stability in the annual number of Plasmodium vivax cases. A close correlation was observed between the seasonal occurence of P. falciparum cases in 1973 and vector densities, and between vector densities and aerial application of agricultural insecticides. Cases of P. vivax appeared about twice as common in the 5 to 14 year age group as in older or younger groups, and cases of P. falciparum seemed only about one-third as frequent in the 0 to 4 year group as in older groups. The attack rate in 1973 was somewhat higher in males than in females. There appeared to be a decrease in parasite densities with age, as well as a direct correlation between parasite densities and the degree of disability (symptoms and "in bed" time) reported by patients.

Adolescent↗
PubMed1977

The competition of molybdate and sulphate ions for a transport system in the ovine small intestine.

The transport of molybdate and sulphate by segments of ovine small intestine in vitro was examined and kinetic constants derived for the late ileum where transport was highest. Sulphate inhibited the uptake of molybdate, probably by competition for sites on a common transport system. The significance of the results with respect to the problem of molybdate toxicity in animals is discussed, and related to the known protective effect of sulphate.

Animals↗
PubMed1977

Recurrent heat exposure: effects on levels of plasma and urinary sodium and potassium in resting and exercising men.

Heat acclimatization was induced in a group of healthy young men by walking on a treadmill (5.6 km/h, 49 degrees C/27 degrees C dry/wet bulb, 90 min/day, 7 d) and confirmed by observing significantly reduced final rectal temperatures and heart rates on the seventh day of exercise in the heat. A second group of men, paired for maximal oxygen consumption and body weight, remained sedentary under identical environmental conditions. While the mild exercise combined with the severe heat conditions induced significant hyperkalemia (p less than 0.02, minimal significance) on both the first and final days, there did occur an attenuated response with significantly (p less than 0.01) reduced plasma K+ after 45 min on the seventh day when compared with first day levels. No significant inter- or intragroup differences in plasma Na+ content of 24-h urine samples showed that men exercising in the heat retained an increased ability to conserve Na+, while sedentary individuals consistently displayed increased excretion of Na+. Thus, we concluded that even the mild exercise described herein effected hyperkalemia at each sampling time, but the level of hyperkalemia was attenuated after acclimatization, and while Na+ was conserved in the exercising men, no such adaptive processes occurred in sedentary individuals.

Acclimatization↗
PubMed1976

Molybdate and tungstate transfer by rat ileum. Competitive inhibition by sulphate.

For both MoO42- and WO42- the maximum rate of uptake by the small intestine of the rat (studied in vitro using the everted sac technique) occurs in the lower ileum. Kinetic constants, derived by a least squares procedure, are compared with those previously obtained for SO42- transport. For both V and Ka, SO42- greater than MoO42- greater than WO42-, with only small differences between sacs IV and V. Mutual inhibition of MoO42- and WO42- transport and inhibition of both by SO42- are competitive processes. This is shown by the generally good agreement between Ka values and derived Ki values and by V values in the presence and absence of the inhibiting species. The three ions SO42-, MoO42- and WO42- are probably transferred across the intestine by a common carrier system. Implications for the sulphate-molybdenum interaction in molybdosis are discussed.

Animals↗