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Biomedical subjects

D Robertson

Publications and source records attributed to D Robertson.

At least 469 records · Page 26Linked to original sources
PubMed1980

Platelet aggregates in peripheral and coronary-sinus blood in patients with spontaneous coronary-artery spasm.

Five out of twenty patients with vasotonic angina had frequent spontaneous attacks with dramatic ST-segment alterations. These attacks were consistently associated with an increase in platelet aggregates in coronary-sinus blood but not arterial blood. This increase in platelet aggregates during coronary-artery spasm suggests a potential causal role for the platelet in this subset of patients with ischaemic heart-disease. However, the increase in platelet aggregates could be secondary to reduced coronary blood-flow.

Adult↗
PubMed1980

Covalent attachment of horseradish peroxidase to the outer surface of liposomes.

We describe a method by which horseradish peroxidase may be attached covalently to the surface of liposomes under conditions which permit minimal non-covalent association of the enzyme with the lipids. The coupling method adopted does not allow the formation of homopolymers of liposomes or peroxidase. For phosphatidylelthanolamine/phosphatidylcholine and stearylamine/phosphatidylcholine and vesicles, minimal disruption of vesicular structure is observed, whilst for phosphatidylserine vesicles, the lipid-protein complex appears to form structures much smaller than 25 nm in diameter. Stearylamine/phosphatidylcholine vesicles have been shown to retain entrapped inulin, and activity measurements for the peroxidase suggest that it is located exclusively on the external surface of the liposome membrane. Peroxidase can be localized histochemically which has permitted the morpholo gical study of the coated liposomes and their interactions with cells.

Animals↗
PubMed1980

60 Hz electric field parameters associated with the perturbation of a eukaryotic cell system.

Roots of Pisum sativum were exposed for seven days to 60 Hz electric fields ranging from 70--430 V/m in an aqueous medium whose conductivity was approximately 0.07 mho/m. (Corresponding current densities in the exposure medium associated with these field strengths ranged from 0.5--3.0 mA/cm2). Control and exposed roots were grown concomitantly in the same tank whose growth medium was continuously circulated. Temperature in the exposure medium was held at a constant 19 degrees C. All experiments were conducted "double blind." Root growth rates were determined daily. No perturbations in root growth were observed with electric fields of 150 V/m; there was a slight effect at 360 V/m, and a pronounced decrease in growth rate occurred at 430 V/m. Root conductivities are comparable to that of the growth medium. Under conditions in which growth inhibition occurs, it is estimated that induced 60 Hz cell membrane potentials would be of the order of 3--8 mV.

Electric Conductivity↗
PubMed1980

Effects of loud tones on the inner ear: a combined electrophysiological and ultrastructural study.

Guinea pigs were exposed to a 10 kHz pure tone and damage to the cochlea was investigated immediately after exposure, or after a recovery period ranging from 18-25 days. Structural damage was assessed using scanning electron microscopy and functional damage estimated using the N1 threshold audiogram. Exposure at 106 dB for 1 h caused obvious abnormalities of outer hair cell stereocilia. The location and extent of this damage was related to the immediate or long term deficits in the N1 threshold audiogram.

Acoustic Stimulation↗
PubMed1980

Acoustic trauma in the guinea pig cochlea: early changes in ultrastructure and neural threshold.

Scanning microscopy was used to examine guinea pig cochleas for structural damage immediately after exposure to a pure tone ranging from 96 to 129 dB SPL. Functional changes to the cochlear neural sensitivity were assessed using the N1 audiogram. principal findings were: (1) The order of damage to receptor cells with increasing sound intensity was OHC1, then IHC, then OHC2 and OHC3. (2) The spatial distribution of damage to OHC1 and IHC differed with IHC tending to show damage mainly in the vicinity of the exposure frequently location and OHC1 damage spreading basal-ward of this point. (3) N1 threshold losses spread progressively to lower frequencies as exposure intensity increased. This was accompanied by an apical spread of damage to the receptor cells.

Animals↗
PubMed1980

Response properties of spiral ganglion neurons in cochleas damaged by direct mechanical trauma.

Electrical activity of single neurons in the spiral ganglion of the guinea pig cochlea was correlated with receptor hair cell damage produced by local mechanical lesions of the organ of Corti. Damage to or loss of hair cells was assessed using scanning electronmicroscopy. Principal finds were (1) neurons emanating from damaged regions showed changes in their tuning curves such as loss of sensitivity, broadening of tuning curves; (2) in some cases, the loss of sharp tuning tip resulted in an apparent shift of the tuning curve to lower frequencies; and (3) apparently pure outer hair cell lesions, of limited spatial extent, could result in the same effects as mixed inner and outer hair cell lesions.

Animals↗
PubMed1980

Autoradiographic studies of the rat renotropic system.

Rat sera, 10-30 h after unilateral nephrectomy (UNI), enhance 3H-thymidine ("3H-Tdr) incorporation into DNA of incubating renal tissue from control rats. Stimulation is even greater when extracts from remaining growing kidneys 20 h after UNI are combined with sera from rats after UNI. UNI extracts, i.e., extracts from the kidney remaining after uninephrectomy, are nonstimulatory alone. UNI sera and UNI sera plus UNI extracts could theoretically augment 3H-Tdr incorporation into renal DNA via dilutional means rather than enhanced DNA synthesis. To determine if our results were secondary to enhanced DNA synthesis, we performed our in vitro assay using the labelling of nuclei via autoradiography as another index. The addition of UNI sera compared to sera from sham-operated rats (SHAM) in seven paired experiments enhanced incorporation of 3H-Tdr into DNA by 30% (p less than 0.02) and the addition of both UNI sera and UNI extracts compared to SHAM sera and SHAM extracts enhanced incorporation by 48% (p less than 0.001). Unlike a dilutional effect, nuclear labelling also increased in these same seven experiments: UNI sera versus SHAM sera increased 25% (p less than 0.05) and UNI sera + UNI extracts versus SHAM sera + SHAM extracts increased 37% (p less than 0.01). We conclude that UNI sera and UNI sera + UNI extracts enhance 3H-Tdr incorporation into DNA by augmenting DNA synthesis, driving cells into the "S" phase. The use of 3H-Tdr incorporation into DNA in our assay does estimate DNA synthesis.

Animals↗
PubMed1980

Elevated plasma free drug concentrations of propranolol and diazepam during cardiac catheterization.

Patients who undergo cardiac catheterization are frequently taking propranolol and are often premedicated with diazepam. Because the intensity of a drug's action is determined by free, or non-protein-bound, levels in plasma, changes in the degree of protein binding may profoundly alter the pharmacologic effect. We examined the effects of heparin on the free levels of propranolol and diazepam in six patients who underwent cardiac catheterization. After heparinization, the free fraction of diazepam increased more than fourfold, from 1.8 +/- 0.1% to 7.9 +/- 1.2% (p < 0.002) and the free levels increased from 2.0 +/- 0.5 to 8.4 +/- 2.2 ng/ml (p < 0.025); the free fraction of propranolol increased from 7.4 +/- 0.9% to 12.5 +/- 1.4% (p < 0.001). The increase in free drug concentration was associated with elevated free fatty acid levels, which rose from 181 +/- 7 micrograms/ml to 596 +/- 119 micrograms/ml (p < 0.02). Increases in the free levels of propranolol and diazepam produced by heparinization during cardiac catheterization may result in increased pharmacolaogic effect, such as excessive sedation or respiratory depression.

Adult↗
PubMed1979

Effect of divalent cations on spontaneous and evoked activity of single mammalian auditory neurones.

Recordings were obtained from single primary auditory neurones in the guinea pig cochlea during perfusion of the scala tympani with solutions containing elevated concentrations of Mg2+, Mn2+ and Co2+, or with lowered concentrations of Ca2+. Such perfusions caused a reversible depression of spontaneous firing rates. This is consistent with the notion that spontaneous firing is the result of background release of excitatory transmitter from cochlear hair cells, in the absence of acoustic stimulation. The above ion modifications also produced varying changes in single neurone response curves to acoustic stimuli. In one half of the 14 neurons studied these changes were also compatible with a classical blockage of synaptic transmission. The other half however, showed little or no change in sensitivity at low frequencies while large threshold elevations occurred at high frequencies.

Action Potentials↗
PubMed1979

Variant angina pectoris: investigation of indexes of sympathetic nervous system function.

One thousand forty-five spontaneous episodes of S-T segment elevation were observed in three patients over a total of 72 days of continuous electrocardiographic monitoring. Eighty-nine percent of episodes were asymptomatic; chest pain tended to occur with episodes longer than 3 minutes, and ventricular ectopy occurred almost exclusively with symptomatic episodes. Nitroglycerin regularly relieved angina or S-T elevation, or both. Plasma and urinary catecholamines and their metabolites were normal. Episodes of variant angina were not associated with a generalized increase in sympathetic outflow because serum catecholamine levels at the onset and termination of the S-T abnormalities were not elevated. Controlled trials of propranolol showed no significant beneficial effect. Propranolol significantly increased the length of episodes of S-T elevation in one patient, increasing ventricular irritability. The overall course of variant angina was quite variable, with spontaneous and long-lasting remissions, necessitating cautions interpretation of clinical trials.

Angina Pectoris↗
PubMed1979

Contraindication to the use of ocular phenylephrine in idiopathic orthostatic hypotension.

We studied the effect of topical ocular application of 2.5% phenylephrine ophthalmic solution in patients with idiopathic orthostatic hypotension and in normal subjects. The normal subjects had no pressor effect to the drug. However, the patients with idiopathic orthostatic hypotension, had a marked pressor response. The maximal pressor response in the four patients averaged 44/27 mm Hg. The usual 10% phenylephrine used in practice could have delivered a fourfold greater amount of drug, and presumably would have led to dangerously high blood pressure responses.

Adult↗