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Biomedical subjects

R N Pittman

Publications and source records attributed to R N Pittman.

102 records · Page 6Linked to original sources
PubMed1980

In vivo microcirculation of a scald burn and the progression of postburn dermal ischemia.

The homozygous hairless mouse ear provides a reproducible model for the study of the microcirculatory changes of the burn wound during and following a scald burn injury. This model has allowed us to correlate the dynamic changes of the microcirculation to progressive zones of injury, which show an approximate tenfold increase in the area of complete capillary occlusion during the first 48 hours after injury. Platelet thromboembolism appears to be the major factor causing this progression of postburn dermal ischemia. Edema (increased skin water content) was greatest in the burned ear at 6 hours after the burn (20 percent greater than control values); edema of the unburned, contralateral ear was significant at 2 hours after the burn (9 percent greater than control values).

Animals↗
PubMed1980

Alterations in beta 1- and beta 2-adrenergic receptor density in the cerebellum of aging rats.

The densities of beta 1 and beta 2-adrenergic receptors were determined in homogenates of cerebral cortex and cerebellum of rats between 3 and 14 mo of age. No change in either receptor population occurred in the cortex during this period. In the cerebellum, a 20--25% decrease in the density of beta 2 receptors and a 350% increase in the density of beta 1 receptors occurred. The increase in beta 1 receptors in the cerebellum may be the result of a decrease in the function of the noradrenergic projections from the locus coeruleus which synapse on cerebellar Purkinje cells.

Aging↗
PubMed1980

Interactions of agonists and antagonists with beta-adrenergic receptors on intact L6 muscle cells.

A binding assay has been developed to characterize beta-adrenergic receptors on intact L6 muscle cells. The affinity of beta-adrenergic receptors for the radioligand iodohydroxybenzylpindolol (IHYP) was the same in membrane preparations and in intact cells when determined by either equilibrium binding or kinetic analysis. The number of specific IHYP binding sites per cell was approximately the same on intact cells as on membranes. The pharmacological properties of antagonists indicated that the receptors on intact cells were identical to those on membranes. However, the beta-adrenergic receptors on intact cells had a 100-400 fold lower affinity at equilibrium for the agonist isoproterenol than did beta-adrenergic receptors on membranes. This low affinity of the receptor for agonists as measured by inhibition of radioligand binding in intact cells has also been observed in C6 (2) and S49 (3) cells. Our results suggest that beta receptors on intact cells after a 1 minute incubation was similar to the KD value for isoproterenol measured in membranes at equilibrium in the presence of GTP. After 1-2 minutes of exposure to a low concentration of agonist, binding of IHYP was no longer inhibited. These results suggest that agonists rapidly convert the beta receptors on intact cells to a state which has a low affinity for agonists. The affinity of the receptor for antagonists did not change during the incubation.

Animals↗
PubMed1975

A new method for the measurement of percent oxyhemoglobin.

A new method is presented for the spectrophotometric determination of percent oxyhemoglobin (percent saturation) in whole blood. The method is based on a theory of light absorption and scattering by particulate suspensions and requires the measurement of optical densities (D) of blood at three closely spaced wavelengths. The contribution of scattering to the optical density at each wavelength is determined from optical density values at two isosbestic wavelengths (546 and 520 nm) and the optical density at the third wavelength (555 nm) is related to the extent of oxygenation of the hemoglobin. The wavelength independence of the scattering contribution (B) induced by red cells was established from 510 and 575 nm. The optical density of red blood cell suspensions was measured with a spectrophotometer and a linear relationship was found between percent saturation and the corrected optical density ratio, (D555 B)/(D546 B). For a given saturation, this ratio was independent of optical path length (0.1-2 mm) and hematocrit (3-50%).

Erythrocytes↗
PubMed1975

Measurement of percent oxyhemoglobin in the microvasculature.

A new method is applied to the determination of percent oxyhemoglobin (percent saturation) in whole blood. The method is based on a theoretical treatment of light absorption and scattering by particulate suspensions and requires the measurement of optical densities (D) of blood at three closely spaced wavelengths. The optical density of red blood cell (RBC) suspensions was measured with a video microdensitometer and a linear relationship was found between percent saturation and the corrected optical density ratio, (D555 B)/(D546 B). For a given saturation, this ratio was independent of optical path length (12 mum-2 mm), hematocrit (3-50%), and RBC velocity (1.5-17 mm/s). The applicability to microvascular measurements has been assessed through the use of TV microdensitometry on micropipettes with flowing RBCs and on microvessels in the hamster cheek pouch.

Densitometry↗
PubMed1975

Oxygen tension: dependent or independent variable in local control of blood flow?

We have looked at a fairly simple model of blood flow regulation at the microvascular level consisting of suffused microvascular preparations and isolated smooth muscles. When the O2 demand of the microvessel preparations was decreased by elevating suffusion solution PO2, changes in wall PO2 indicated that only the smallest microvessels could be controlled by a direct effect of oxygen. In vivo and in vitro studies of the oxygen sensitivity of smooth muscle indicated that even the smaller vessels were probably not directly controlled by oxygen availability during a free flow state, since measured perivascular PO2's did not fall to levels low enough to alter contractile performance of the vascular smooth muscle. Our data indicate that in any condition in which flow is interrupted for periods in excess of about 30 sec, one might anticipate vascular relaxation due to oxygen lack. It was judged resonable to extrapolate our findings to autoregulation of blood flow in resting skeletal muscle and to responses to modest exercise. Our data indicate that it is improbable that oxygen acts by a direct effect on the smooth muscle under these conditions. On the other hand, they suggest that a direct effect of oxygen might well be important in causing postocclusion hyperemia.

Animals↗
PubMedDate not supplied

Determination of red blood cell velocity by video shuttering and image analysis.

A novel modification of conventional video imaging techniques has been developed to determine the velocity of red blood cells (RBCs), which offers compatibility with existing video-based methods for determining blood oxygenation and hemoglobin concentration. Traditional frame-by-frame analysis of video recordings limits the maximum velocity that can be measured for individual cells in vivo to about 2 mm/s. We have extended this range to about 20 mm/s, by electronic shuttering of an intensified charge-coupled device camera to produce multiple images of a single RBC in the same video frame. RBCs were labeled with fluorescein isothiocyanate and the labeled cells (FRBCs) were used as probes to determine RBC velocities in microvessels of the hamster retractor muscle. Velocity was computed as the product of the distance between centroids of two consecutive image positions of a FRBC and the shuttering frequency of the camera intensifier. In vitro calibrations of the system using FRBC and Sephadex beads coated onto a rotating disk yielded an average coefficient of variation of about 6%. Flow conservation studies at bifurcations indicated that the maximum diameter of microvessels below which all the FRBCs in the lumen could be detected was 50 microm. The technique was used to estimate mean-FRBC velocity distributions in vessels with diameters ranging from 8 to 50 microm. The mean-FRBC velocity profiles were found to be blunter than would be expected for Poiseuille flow. Single FRBCs tracked along an unbranched arteriole exhibited significant temporal variations in velocity.

Animals↗
PubMedDate not supplied

Interaction between oxygen and the blood vessel wall.

Blood vessels in vivo respond to changes in the supply of oxygen relative to its demand. Whether the vessels which participate in such vasoregulatory responses are directly affected by oxygen remains an open question. Most studies of oxygen sensing by blood vessels have been carried out on strips, rings or segments isolated from relatively large vessels. These preparations are generally sensitive to oxygen from 0 mm Hg to some upper PO2 (10 to 240 mm Hg) whose value depends on experimental conditions. It appears unlikely that reduced energy production secondary to tissue hypoxia is directly responsible for the relaxation usually observed when PO2 is lowered below a critical value. Evidence that an oxygen-linked chemical mediator such as adenosine or prostacyclin is involved in contractile responses to lowered PO2 has been obtained. The site of action of oxygen could be anywhere within the vascular wall, but current evidence suggests a prominent role for the endothelial cells. At present extrapolation of these results to resistance vessels in vivo must be carried out with caution due to potential differences in the behaviour of microvessels relative to large vessels.

Adenosine↗