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Biomedical subjects

G Porter

Publications and source records attributed to G Porter.

At least 73 records · Page 4Linked to original sources
PubMed1978

Comparative nephrotoxicity of gentamicin and tobramycin in rats.

A rat model was utilized to compare the nephrotoxic potential of gentamicin and tobramycin. Gentamicin, 40 mg/kg per day, predictably produced renal failure and morphological evidence of proximal tubular necrosis over 14 days of treatment. An identical dosage of tobramycin was associated with only minimal morphological changes and normal concentrations of serum creatinine and blood urea nitrogen. Similar results were obtained even after the tobramycin dosage was tripled to 120 mg/kg per day. A decrease in urine osmolality, mechanism unknown, was observed in all aminoglycoside-treated rats, but the lowest osmolalities were found in the gentamicin-treated rats. According to both histological criteria and renal function measurements, gentamicin was more nephrotoxic than tobramycin in this animal model.

Animals↗
PubMed1978

Gentamicin and tobramycin nephrotoxicity. A morphologic and functional comparison in the rat.

Fischer 344 rats were treated with tobramycin or gentamicin, 40 mg/kg/day, for up to 10 days or with tobramycin, 120 mg/kg/day, for up to 14 days. Serum creatinine and BUN at the time of sacrifice were determined, and kidney tissues were examined by light and electron microscopy. Rats receiving gentamicin demonstrated progressive renal proximal tubular necrosis which was nearly universal at the end of 10 days. Their BUN and creatinine levels rose progressively over the same period. Even at the higher dosage, tobramycin therapy resulted in only rare foci of proximal tubular necrosis and minimal elevation of BUN and creatinine. Although they occurred later and were substantially less severe, the ultrastructural changes induced by tobramycin were the same as those seen following gentamicin administration. These results indicate that the mechanism of tobramycin-induced renal injury is probably similar to that of gentamicin and that tobramycin is significantly less nephrotoxic in this experimental model.

Animals↗
PubMed1977

Excited state annihilation in the photosynthetic unit.

The kinetics of the in vivo fluorescence decays and fluorescence yields, as a function of excitation intensity, have been analysed with a model using excited state annihilation and time-dependent quenching processes. Triplet states, formed in the singlet-singlet annihilation processes, account for additional quenching of singlet states and the persistence of annihilation at longer times than the fluorescence life-time. Together these processes give a satisfactory account of existing experimental data of the intensity dependence of fluorescence in vivo.

Chlorophyll↗
PubMed1977

Intensity effects on the fluorescence of in vivo chlorophyll.

A technique for measuring relative quantum yields of fluorescence with a picosecond streak camera is described. We show that Chlorella pyrenoidosa exhibit an intensity dependent quantum yield when irradiated with single picosecond light pulses. This effect also occurs under conditions that inhibit the activity of the reaction centres, which can therefore be excluded as the cause. When a pulse train (pulse separation 6.9 ns) was used, the quantum yield was further reduced by the light absorbed from previous pulses, which indicates the formation of a quenching species having a relatively long lifetime. Absolute quantum yields calculated from the fluorescence decay show that single excitation pulses of 3 - 10(13) photons/cm2 give results comparable to those obtained by very low intensity methods.

Chlorella↗
PubMed1977

Picosecond laser study of fluorescence lifetimes in spinach chloroplast photosytem I and photosystem II preparations.

Fractions enriched in either Photosystem I or Photosystem II have been prepared from chloroplasts with digitonin. A more detailed analysis of the decay kinetics of fluorescence excited by a picosecond laser pulse has been possible compared to experiments with unfractionated systems. The Photosystem I fractions show a very short component (less than or equal to 100 ps) at room temperature which is apparently independent of pulse intensity over the range of photon densities used (5 - 10(13)--1 - 10(16) photons cm-2). The Photosystem II fraction has a short initial lifetime at room temperature which is strongly intensity-dependent approaching 500 ps at low photon densities, but decreasing to close to 150 ps at the highest photon densities. All of these room temperature decays appear to be non-exponential, and may possibly be fitted by at t1/2 expression, expected from a random diffusion of excitations via Förster energy transfer. On cooling to 77K, lifetimes of both Photosystem I and Photosytem II increase, the lengthening with Photosystem I being more striking. The Photosystem I decays become intensity dependent like the Photosystem II, and at the lowest photon densities decays which are more nearly exponential within the experimental error give initial lifetimes of about 2 ns. The non-exponential decays seen at high photon densities appear to fit a t1/2 expression.

Chloroplasts↗
PubMed1977

Cell-mediated immunity in vasectomized rhesus monkeys.

Cell-mediated immunity in rhesus monkeys that had been vasectomized for 2, 4, 7, or 11 years was measured by lymphocyte blastogenesis following stimulation with concanavalin A, phytohemagglutinin (PHA), and pokeweed mitogens. Several of the 7- and 11-year vasectomized animals had significantly reduced PHA reactivity when compared with control animals, and the percentage of animals with reduced PHA reactivity increased with time after vasectomy.

Alpha-Globulins↗
PubMed1977

Kinetic differences between uterine and renal renins in the dog.

It has previously been reported that in the dog the Michaelis constant (Km) of renal renin with respect to homologous plasma substrate is the same as that for the angiotensin-generating enzyme extractable from the myometrium during pregnancy. We have reexamined the kinetics with a different methodology. Enzyme preparations from dog kidneys, the uterus of a nonnephrectomized pregnant bitch, and the uterus of a nephrectomized pregnant bitch were used. The substrate, prepared by diluting plasma from a nephrectomized, hysterectomized pregnant bitch, had a maximum endogenous substrate concentration of 1,750 ng/ml angiotensin I equivalents. Lineweaver-Burk kinetic analysis was used to calculate the Michaelis constants at pH 6.2. The Km of the renal enzyme was 720 ng/ml, of the enzyme prepared from the nonnephrectomized uterus 1,570 ng/ml, and of the nephrectomized dog uterus 1,500 ng/ml. The uterine enzyme was not activated by transient acid treatment, in contrast to renins reported from other sources. The data support the concept of biochemical heterogeneity of the two enzymes in the dog.

Angiotensinogen↗
PubMed1976

Fluorescence lifetimes of Chlorella pyrenoidosa.

The flucrescence decay of Chlorella pyrenoidosa has been investigated under a variety of conditions in the picosecond and nanosecond time regions. Most of the fluorescence is accounted for by an expression of the form I(t) = I0exp-(At+Bt1/2) though an additional exponential term is required to include a weak component of lifetime 32 ps observable only at the higher pulse intensities. This interpretation reconciles earlier and apparently conflicting data. The weak 32 ps component may be associated with Photosystem I, although the possibility that it is an artefact of the high intensity pulses used cannot be excluded at present. The main fluorescence, described by the equation above is attributed to the antenna chlorophyll and is of the form which would be expected from a single light harvesting array with trapping at randomly distributed sites.

Chlorella↗
PubMed1976

A light and electron microscopic analysis of gentamicin nephrotoxicity in rats.

The sequence of proximal tubular damage and repair after gentamicin sulfate administration was studied by light and electron microscopy in Fischer 344 rats. The drug was administered at a dose of 40 mg/kg for up to 14 days. Although epithelial destruction was progressive with time, the extent and degree of tubular damage varied among animals at each interval. Tubule regeneration began to occur by the tenth day despite continued drug administration. Regenerating cells appeared to originate from residual epithelial cells in areas of tubular damage. The morphologically immature regenerating cells are apparently metabolically immature as well and appear not to be susceptible to toxic effects of the drug. Tubules were repopulated by 3 days following cessation of gentamicin administration. Except for foci of tubular atrophy and interstitial fibrosis, cortical tissues were comparable to controls ultrastructurally at the end of 31 days.

Acute Kidney Injury↗
PubMed1975

Estimation of fetal weight from ultrasonic measurement of trunk circumference.

A new method of estimating fetal weight from the circumference of the fetal trunk, measured by ultrasound, is described. Comparison of weights estimated in this way with the actual birth weights of 50 fetuses, delivered not more than 48 hours later, shows a mean error in prediction of only 75 g, and in 94 per cent the error was less than 145 g. With such accuracy, the method is of clinical value, particularly in anticipating difficult delivery and in monitoring growth of the fetus at risk.

Abdomen↗