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Biomedical subjects

B J Barber

Publications and source records attributed to B J Barber.

34 records · Page 2Linked to original sources
PubMed1987

Lymph protein concentration in initial and collecting lymphatics of the rat.

Lymph samples were obtained from villus initial and mesenteric prenodal collecting lymphatics of the anesthetized rat using standard micropuncture techniques. The protein concentrations of the lymph samples were determined using a fluorometric microassay. These procedures were performed on preparations either superfused with a modified Krebs solution or covered with paraffin oil. The protein-concentrating ability of the intestinal lymphatics was evaluated to test the osmotic theory of lymph formation. The mean initial lymph protein concentration in superfused preparations was 2.08 g/dl (SE = 0.20). The lymph protein concentration in collecting vessels in superfused preparations was 2.20 g/dl (SE = 0.19). The protein concentration from initial lymphatics in oil-covered preparation was 2.48 g/dl (SE = 0.17). The lymph protein concentration in collecting vessels in oil-covered preparations was 2.32 g/dl (SE = 0.15). The difference between initial and collecting lymph protein concentration found was an order of magnitude lower than that predicted by the osmotic theory. These results cast serious doubts on the effectiveness of the osmotic mechanism of lymph formation as it is presently defined.

Animals↗
PubMed1987

Variations in rat mesenteric tissue thickness due to microvasculature.

Studies of microvascular, tissue and lymphatic transport using microphotometric and microfluorometric techniques are potentially subject to artifact due to variations in tissue specimen thickness. Absorbance techniques utilize the Lambert-Beer law in which A = log I0/I = act, where A is absorbance, I0 is incident light intensity, I is transmitted intensity, a is an absorbance coefficient, c is concentration of substance, and t is path length. If differences in t are known to be present, then inferences of changes in c from changes in A become suspect. In microfluorometry the amount of light gathered is proportional to the number of fluorochromes in the effective cuvette, which is determined by the microscope's numerical aperture and the sample thickness. If variations in thickness are known to occur, the effective cuvette volume may be changing; therefore, inferences of changes in fluorochrome concentration from changes in intensity become suspect. Existing data suggest that rat mesentery is 15-30 microns thick, but variation over a tissue region is unknown. Our goals are to determine thickness variation in avascular, fat-free mesenteric tissue regions; thickness variation near blood vessels; and average tissue thickness. Sprague-Dawley rats were anesthetized with Inactin. Mesenteric tissue from a loop of small intestine was draped over a platform for observation; thickness was measured with an oblique microscope and a microgravimetric technique. The average variation in avascular fat-free tissue was 1.1 micron/100-microns distance, and average thickness was 17.4 microns. There was a significant increase in thickness over the microvasculature.

Animals↗
PubMed1987

Larval Sulcascaris sulcata from calico scallops, Argopecten gibbus, along the southeast coast of the United States.

Adductor muscles of calico scallops, Argopecten gibbus, collected off the southeastern coast of the United States from May 1982 to December 1984 were examined for the presence of larvae of the parasitic nematode, Sulcascaris sulcata. Infection intensity, prevalence, and larval length were all positively correlated (P less than 0.001) with scallop shell height (age). Prevalence was generally highest in December and lowest in August as a result of yearly trends in the age structure of the scallop population. Prevalence was not influenced by latitude or depth over the ranges examined. The rate of infection of marine molluscs by S. sulcata is generally related to the degree and length of exposure to third-stage larvae, whose distribution is essentially that of the marine turtle definitive host. Thus, over the wide geographic area of the east coast of the U.S., overall rates of infection decrease with increasing latitude.

Animals↗
PubMed1986

Chronic measurement of cardiac output in unanesthetized rats using miniature thermocouples.

A thermodilution technique is described for measuring steady-state cardiac output (CO) in conscious rats for periods of 2-3 wk. The method utilizes small implantable aortic thermocouples inserted via the femoral artery at the time of placement of other chronic indwelling catheters. Data are presented to validate the accuracy and reproducibility of the technique by acute in situ comparison with electromagnetic flowmeter measurements. Responses in chronically instrumented rats were tested with hemorrhage and infusions of vasodilator and vasoconstrictor agents administered repeatedly over a period of 9 days. The results show that the system is capable of measuring CO chronically and provides reproducible responses for periods of at least several weeks. We conclude that these methods provide a single, inexpensive, and accurate way to measure steady-state CO in conscious, unrestrained rats.

Animals↗
PubMed1985

Effects of altered ambient temperature on metabolic rate during CO2 inhalation.

The purpose of this study was to determine if the changes in O2 consumption (VO2) during CO2 inhalation could in part be due to stimulation of thermogenesis for homeothermy. Twelve ponies were exposed for 30-min periods to inspired CO2 (PIco2) levels of less than 0.7, 14, 28, and 42 Torr during the winter at 5 (neutral) and 23 degrees C ambient temperatures (TA) and during the summer at 21 (neutral TA), 30, and 12 degrees C. Elevating TA in both seasons resulted in an increased pulmonary ventilation (VE) and breathing frequency (f) (P less than 0.01) but no significant increase in VO2 (P greater than 0.05). Decreasing TA in the summer resulted in a decrease in VE and f (P less than 0.01) but no significant change in VO2 (P greater than 0.05). At neutral TA in both seasons, VO2 increased progressively (P less than 0.05) as PIco2 was increased from 14 to 28 and 42 Torr. The increases in VO2 during CO2 inhalation were attenuated (P less than 0.05) at elevated TA and accentuated at the relatively cold TA in the summer (P less than 0.05). Respiratory heat loss (RHL) during CO2 inhalation was inversely related to TA. Above a threshold RHL of 2 cal X min-1 X m-2, metabolic heat production (MHP) increased 0.3 cal X min-1 X m-2 for each unit increase in RHL during CO2 inhalation at the neutral and elevated TA. However, during cold stress in the summer, the slope of the MHP-RHL relationship was 1.6, indicating an increased MHP response to RHL.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Analysis of picogram quantities of protein in subnanoliter-size samples.

The ability to measure protein concentration in subnanoliter volumes would be helpful in many biological studies. A microassay for measuring nanogram protein quantities in nanoliter-size samples and an ultramicroassay for measuring picogram quantities in picoliter samples were developed to measure lymphatic protein concentration. Aliquots of a sample solution were mixed with an o-phthalaldehyde mercaptoethanol reagent using micropipetting techniques. Reaction product fluorescence was measured using a modified Leitz MPV-1 microscope as a microfluorometer. Fluorescence varied linearly with albumin concentrations between 1 and 8 g/100 ml. A typical microassay measuring albumin standards at 0.0, 1.0, 2.0, and 4.0 g/100 ml yielded a linear regression of y = 207x + 60 (r = 0.99). Minimum detectable protein concentration was 0.125 g/100 ml. The SE for the albumin standards varied from 0.02 to 0.17 g/100 ml. An ultramicroassay measuring similar standards yielded a linear regression of y = 1180x + 109 (r = 0.96). Minimum detectable protein concentration was 0.028 g/100 ml. The SE for the standards varied from 0.01 to 0.32 g/100 ml.

Albumins↗
PubMed1984

Influence of vasopressin and angiotensin on baroreflexes in the dog.

Cardiovascular responses to step-changes of carotid sinus pressure were evaluated at normal and elevated levels of plasma arginine vasopressin in anesthetized neurohypophysectomized dogs (n = 12). Arginine vasopressin influenced autonomic function in two ways: first, maximum carotid reflex gain increased; second, cardiac output was decreased. The enhancement of reflex strength was observed only in response to decreases of intrasinus pressure below the equilibrium point (pressures of between 60 and 105 mm Hg). Aortic pressure rose twice as high for a given decrease of intrasinus pressure, elevations of total peripheral resistance responses were triple those observed at normal plasma arginine vasopressin. In this way, arginine vasopressin more than doubled the ability of the carotid reflexes to return a drop in arterial pressure to normal. Arginine vasopressin enhancement of reflex gain was not observed with elevations of intrasinus pressures above the equilibrium point. Elevation of aortic pressure expected from the vasoconstrictor actions of infused arginine vasopressin were buffered by associated reductions in cardiac output. Vagally mediated bradycardia was consistently observed with elevated arginine vasopressin, but the reflex response of heart rate to step-changes of intrasinus pressure was unchanged. Time control studies in five neurohypophysectomized dogs indicated no significant change in carotid reflex response over the 3- to 4-hour protocol. Comparison of reflex responses in anephric dogs (n = 8) at low and elevated levels of angiotensin II indicated that this vasoactive peptide did not significantly alter reflex responsiveness. We conclude that arginine vasopressin enhances the ability of the carotid reflexes to normalize decreases of arterial pressure, but buffers a rise in pressure from its own vasoactive properties by initiating a fall of cardiac output.

Angiotensin II↗
PubMed1982

Reactive and exercise hyperemia during high levels of adenosine infusion.

In these experiments we tested the quantitative importance of adenosine as a mediator in the regulation of muscle with blood containing adenosine at concentrations more than 1,000 times the normal resting adenosine level (1, 7) so that the effect of any endogenously released adenosine would be miniscule in comparison with the effect of this perfused adenosine. Therefore, any major blood flow responses that should occur while the muscle remained continuously under the influence of the perfused adenosine could hardly be ascribed to endogenous adenosine. At the onset of the perfusion with the adenosine the blood flow increased approximately sevenfold. However, over 1-3 h of continued perfusion, the blood flow returned to or near to control despite the extreme amounts of adenosine. Then, while the muscle was still exposed to the adenosine, both reactive hyperemia and exercise hyperemia were elicited for varying time periods and varying degrees for a total of 96 separate measurements in 12 preparations. In all instances the increases in blood flow during hyperemia were almost exactly identical to those recorded prior to adenosine perfusion. Because it would have been almost impossible for the small amounts of endogenous adenosine to cause the large hyperemia responses in the face of the extreme amounts of perfused adenosine, it is concluded that both the reactive and exercise hyperemia responses are probably caused either entirely or almost entirely by factors other than adenosine.

Adenosine↗
PubMed1980

An inexpensive pressure telemetry system.

An inexpensive telemetry system using transducers and recorders commonly available, i.e., Statham and Grass, is described. The direct-current signal of a Statham transducer is applied to a voltage-controlled oscillator, thereby frequency encoding the pressure sensed by the transducer. This encoded signal frequency modulates a Colpitts oscillator, which acts as a radio-frequency oscillator-transmitter in the 88- to 108-MHz band. This transmitter and transducer, along with a rechargeable NiCd battery pack (total wt 0.5 kg), are mounted in a canvas jacket and worn by a dog previously prepared with a chronic indwelling arterial catheter. With a fully charged battery pack, a signal can be transmitted up to 250 ft for 50 h. A frequency-modulation automotive receiver, powered by and interfaced with a Grass 7B recorder, receives the signal and drives a tachometer circuit that reconverts the audio-frequency signal to a voltage proportional to pressure. This voltage is then applied to the driver amplifier of the Grass to produce a charted record. This system introduces no distortion as seen by comparison of direct and telemetered signals and is drift free for intervals exceeding 24 h.

Animals↗
PubMed1980

The energetics of lymph formation.

A very important unanswered problem is the source of the energy required for formation of lymph. The most widely held theory has been that fluid filters from the capillaries, flows through the tissues, and then enters the lymphatic as a result of a continuous positive pressure gradient from the blood capillary to the lymphatic capillary. However, this fails to account for the negative pressures that have been measured by implanted perforated capsules and by the wick technique, both of which suggest that the interstitial free fluid pressure is negative. Furthermore, because the fluid in the tissue gel is in equilibrium with the free fluid, it has a chemical potential equivalent to the negative pressure of the free fluid. At present, the only probable source of energy that could create the negative hydrostatic pressure in the free fluid and the equivalent negative chemical potential in the intragel fluid is a lymphatic suction pump. Unfortunately, the existence of this has not yet been proved, but mechanisms by which the terminal lymphatic system could act as a suction pump have been proposed.

Capillaries↗
PubMedDate not supplied

Texture analysis of protein distribution images to find differences due to aging and superfusion.

Many pathologies are age-related, e.g., cardiovascular disease generally occurs in midlife and cancer later in life. This suggests that aging predisposes the body to pathology. Plasma protein spatial distribution images of rat mesentery extracellular matrix (ECM) show texture due to the ECM structures, and there is an age-related decrease in tissue protein that may be related to matrix structure changes. The objective of this study was to compare changes in protein image texture under two conditions: superfusion with normal saline solution and aging. The decrease in soluble protein concentration during superfusion is a washout process, while the mechanism for the age-related decrease in tissue protein is unknown. Therefore, effects of aging and superfusion on tissue protein image texture were compared. Spatial co-occurrence matrix and Fourier analysis techniques have been used for texture evaluation. Superfused images showed a more uniform protein texture. There were gradual age-related changes in image texture parameters. Entropy increased with age from 140 to 630 days, indicating that protein distribution became more disorganized. The results suggest that changes in protein image texture are due to age-related alterations in matrix structure because removing only protein by superfusion had opposite effects on texture parameters.

Aging↗
PubMedDate not supplied

Analysis of the effect of bilateral sympathetic stimulation of cerebral and cephalic blood flow in the dog.

Unilateral stimulation of the cervical sympathetic in dogs had no effect on cerebral blood flow (CBF) measured by the venous outflow technique. Since this technique measured CBF from both cerebral hemispheres, small changes induced by unilateral stimulation could have been masked by a large constant CBF measured from the contralteral hemisphere. To test this possibility the effect of simultaneous bilateral sympathetic stimulation was studied when the dog was breathing either normal air or a gas mixture of 10%CO2. During normocapnia, no changes in CBF occurred; during hypercapnia CBF increased 19% following passively the increase in blood pressure. These data indicate that bilateral stimulation of extracranial sympathetic nerves does not exert a significant effect on CBF. We show mathematically and experimentally that unoccluded anastomses will cause CBF to appear to decrease in response to sympathetic stimulation. This may explain why others have observed changes in CBF during sympathetic stimulation.

Animals↗