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B R Duling

Publications and source records attributed to B R Duling.

At least 37 records · Page 2Linked to original sources
PubMed1987

Capillary grouping in hamster tibials anterior muscles: flow patterns, and physiological significance.

We have used fluorescein-labeled albumin and epifluorescence videomicroscopy to visualize the organization and flow patterns in the capillaries of a postural muscle, the tibialis anterior, in the pentobarbital-anesthetized hamster. Video tape records were made of overlapping microscope fields comprising portions of the muscle up to two millimeters in length and as much as 180 micron in depth. Three-dimensional reconstructions made from these tapes incorporated observations on flow patterns and geometry of the microvessels. The microcirculation in the tibialis was found to be arranged in repeating modules or 'units', consisting of approximately 15 capillaries supplied by a common arteriole and drained by a common venule. The mean distance from arteriole to venule in a unit was 855 +/- 233 micron (X +/- SD) and the mean capillary length was 805 +/- 330 micron. Flow in the capillaries within a unit was almost entirely concurrent, and there was little interchange of blood flow between the capillaries of adjacent units. The flow in capillaries of adjacent units was both countercurrent and concurrent. For each capillary, a count of the adjacent capillaries with concurrent and countercurrent flow was made. The ratio of concurrent to countercurrent flow varied from 2.4 to 4.3, being greatest at the midpoint of the unit and least at the arterial and venous ends. Our observations suggest that the capillaries of striated muscle are arranged in modules which may function as the fundamental control and distribution elements in the microcirculation.

Animals↗
PubMed1987

Propagation of vasodilation in resistance vessels of the hamster: development and review of a working hypothesis.

In many tissues, a substantial fraction of total vascular resistance resides in the feed arteries that give rise to the microcirculation. We have explored the thesis that control of tissue blood flow is integrated over several levels of the vascular network, including feed arteries and microvessels. In response to muscular contraction, feed arteries (resting diameter 100-125 microns) of hamster cremaster and gracilis muscles dilated by 20-25%. Acetylcholine applied to distal microvessels of the cremaster induced a dilation that ascended into feed arteries not having direct contact with acetylcholine. In the hamster cheek pouch, iontophoretic application of acetylcholine onto an arteriole (diameter 20-30 microns) triggered a vasodilation that propagated along the arteriole. Propagation was not dependent on blood flow, indicating that the dilator response was conducted along the vessel wall. We found that preventing diameter changes in an arteriole segment along the apparent conducting pathway did not block propagated vasodilation, indicating that propagation was not mediated by a myogenic mechanism requiring changes in smooth muscle length. We investigated whether the conduction of a vasodilatory stimulus may be mediated by either a neural plexus intrinsic to microvessels or cell-cell coupling between the cells composing the arteriole. Tetrodotoxin (10(-6) M) did not block propagated vasodilation, indicating that propagation is not mediated by a neural pathway. Hypertonic sucrose solution applied to an arteriole segment along the apparent conducting pathway attenuated propagation significantly, which is consistent with its reported effect to decouple gap junctions between cells. Thus, propagated vasodilation in arterioles may be mediated by direct cell-cell conduction.

Acetylcholine↗
PubMed1986

Flow control among microvessels coordinated by intercellular conduction.

Optimal distribution of blood flow requires coordination of vasodilation among resistance vessels. During hyperemia, blood vessels dilate upstream from the initiating stimulus. Spreading vasodilation independent of flow changes has not been previously demonstrated. In the present study, iontophoresis of acetylcholine adjacent to single hamster cheek pouch arterioles in situ (diameter, 20 to 37 micrometers) induced a rapid bidirectional dilation that was not attenuated when blood flow was eliminated with vascular occlusion. This finding indicates that a vasodilatory stimulus is conducted along the arteriole and demonstrates the existence of a mechanism of intercellular communication that is capable of coordinating diameter changes among resistance vessels.

Acetylcholine↗
PubMed1986

Communication between feed arteries and microvessels in hamster striated muscle: segmental vascular responses are functionally coordinated.

Pressures in the primary arterioles of the cremaster muscle are reported to be approximately 50% of systemic, indicating that arterial resistance proximal to microvessels is high and may limit maximal blood flow. With no change in arterial resistance, increases in perfusion normally associated with muscle work either could not occur or would require increments in systemic pressure far greater than those actually observed in vivo. Therefore, we hypothesized that the small arteries feeding the muscle may participate in the hyperemic response. To test this hypothesis, male golden hamsters (n = 31, 118 g) were anesthetized (pentobarbital, 70 mg/kg i.p.), and the right cremaster was opened to expose its feed arteries, which originated from the iliac artery. Preparations were superfused and maintained at 35 +/- 1 degree C. Feed arteries had substantial tone, as shown by the fact that topical acetylcholine, applied at supramaximal concentration, dilated these vessels from 115 +/- 8 microns at rest to 158 +/- 9 microns (mean +/- SE; n = 38 vessels; p less than 0.01), corresponding to an estimated 4.4-fold increase in conductance. Stimulation of the sectioned motor nerve (8 Hz, 30 seconds) induced striated muscle contraction and increased feed vessel diameter from 93 +/- 5 microns to 116 +/- 5 microns (n = 14; p less than 0.01), consistent with a 2.6-fold increase in conductance. A 5-minute occlusion of the iliac artery resulted in feed artery dilation of similar magnitude. Supramaximal doses of acetylcholine applied topically to the distal portions of the cremaster resulted in striated muscle contraction and a dilation that propagated upstream to increase feed artery diameter by 25%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Coordination of mural elements and myofilaments during arteriolar constriction.

Arterioles undergo major morphological changes during vasoconstriction. We used transmission electron microscopy to study wall morphology in both dilated and constricted microvessels to understand the cellular basis of these changes. The relation between the orientation and density of myofilaments and the distribution of dense bodies was analyzed with respect to the level of microvessel tone. The data show a strong correlation between the degree of arteriolar constriction and both the orientation and density of myofilaments. In dilated arterioles, myofilament orientation was predominantly circumferential across the entire smooth muscle cell, averaging 84 +/- 2 degrees (SEM) relative to a radial reference line. In vessels constricted to 50% of their maximal diameter, myofilament orientation was dependent upon the location within the cell, being largely circumferential at the adventitial border (77 +/- 4 degrees) and shifting to a radial arrangement at the intimal border (36 +/- 5 degrees). The reorganization of myofilaments during constriction was associated with a decrease in myofilament density at the intimal-medial border of the smooth muscle cells. The decrease in myofilament density resulted from a selective withdrawal of myofilaments from periluminal areas where "ridges" had formed. Our observations suggest that an ordered distribution of membrane-associated dense bodies along the periluminal aspect of the smooth muscle cells is responsible for both the myofilament reorganization and ridge formation during vasoconstriction. Results of the present study are incorporated into a hypothetical model of arteriolar ultrastructure compatible with the mural reorganization observed during vasoconstriction.

Actin Cytoskeleton↗
PubMed1985

Evidence that capillary perfusion heterogeneity is not controlled in striated muscle.

We tested the hypothesis that the heterogeneity of capillary blood flow distribution in striated muscle is inversely proportional to tissue blood flow by examining the patterns of red blood cell flow in the capillaries of hamster tibialis anterior muscles. Capillary red blood cell velocities and capillary red blood cell fluxes were measured as indexes of blood flow and red blood cell distribution in vasoconstricted and vasodilated vascular beds of resting and working striated muscle. Standard statistical parameters describing dispersion of data (standard deviation and coefficient of variation) in addition to measured and normalized histograms were compared across treatments. With vasodilation the standard deviations of both variables increased linearly with the means, and measured distributions became broader. The coefficients of variation and normalized distributions of both variables did not differ across treatments. These observations do not support the idea that the heterogeneity of capillary perfusion is controlled. Rather they suggest that fractional flow dispersion among capillaries is constant and independent of muscle blood flow and/or O2 demand.

Animals↗
PubMed1984

Inaccuracies in blood flow estimates in microvessels during arteriolar vasoconstriction.

The effect of vasomotor tone on blood flow estimates was evaluated in the hamster cheek pouch and cremaster muscle microcirculation. The products of arteriolar cross-sectional area and red blood cell velocity were calculated in three different cases: (1) at arteriolar bifurcations, (2) in short segments of an arteriole constricted by iontophoretic application of norepinephrine, and (3) at randomly selected second- and third-order arterioles. Vasodilation of the microcirculation was induced by topical application of adenosine. Vasoconstriction was induced by elevation of superfusion solution PO2. If true volume flow is accurately estimated by this method then: the sum of measured branch flows at a bifurcation should equal feed flow; measured flow through constricted arteriolar segments should equal flow proximal or distal to the constricted segment; and, following experimental manipulations, relative changes in estimated flow in second- and third-order arterioles should be equal. Our findings suggest that the blood flow estimates were not always accurate. The sum of branch flows was equal to feed flow only across bifurcations with low or resting vascular smooth muscle tone. During vasoconstriction, feed flow averaged 40% higher than the sum of downstream flows. In addition, estimated flow was 15% lower in constricted segments of an arteriole compared to dilated contiguous segments of the vessel. During alterations in vasomotor state, estimated fractional changes in flow in second- and third-order arterioles differed by more than sixfold. Therefore, blood flow estimates with the dual-slit method may not be reliable under conditions of high vasomotor tone. We speculate that the error may result largely from uncertainties in the diameter measurement.

Adenosine↗
PubMed1984

Distribution of capillary blood flow in the microcirculation of the hamster: an in vivo study using epifluorescent microscopy.

In vivo epifluorescent microscopy (EPI) was used to study capillary perfusion in superfused hamster cheek pouch, and cremaster and sartorius muscle preparations. In cheek pouches and cremaster muscles, in vivo epifluorescence microscopy (EPI) was compared to in vivo transillumination microscopy (TRANS) and the former was found to allow detection of a larger number of capillaries--34% more capillaries in cheek pouch and 21% more in cremasters were observed with EPI. The fraction of capillaries containing erythrocytes alone, plasma alone or plasma plus red cells was determined in all three tissues. Also, the fraction of capillaries unperfused was noted. Less than 2% of the capillaries contained plasma alone. The number of capillaries which contained stationary erythrocytes varied with vasomotor tone. In control cremaster and sartorius muscles 17 and 13% of observed capillaries were unperfused but contained erythrocytes. Ninety-eight percent of capillaries contained stationary erythrocytes in cremaster muscles vasoconstricted with 21% oxygen. From these observations we conclude (1) functional capillary counts obtained with TRANS may represent underestimates of the true number; (2) plasma shunts do not appear to be a significant factor in normal microcirculatory function in the hamster cheek pouch, or in cremaster and sartorius muscles; (3) since unperfused capillaries contain red cells, red cell counts in histological sections will overestimate functional capillarity. The magnitude of the overestimation will be a function of vascular tone and capillary hematocrit.

Animals↗
PubMed1984

Effect of norepinephrine on penetrating arterioles of rat cerebral cortex.

Penetrating intracerebral arterioles from the rat with mean resting diameters of 26.3 +/- 2.8 micron and maximal diameters of 37.4 +/- 2.5 (SE) micron were isolated, cannulated, and perfused in vitro. Spontaneous tone development and hydrogen ion reactivity indicated that vessels were relatively undamaged and viable. The norepinephrine (NE) reactivity of intracerebral penetrating arterioles is pH dependent. Vessels studied at extraluminal pH 7.30 were unresponsive to NE up to concentrations of 10(-6) M. At NE concentrations above 10(-6) M, vessels dilated to diameters approximately 110% of control. At pH 7.80, vessels contracted to diameters between 75 and 80% of control in response to extraluminal NE concentrations between 10(-11) and 10(-6) M. Vessels in 10(-6) M phentolamine failed to respond to 10(-8) M NE at pH 7.30 and pH 7.80. An aliquot of 10(-8) M NE solution made up at pH 7.80 failed to induce vessel contraction when the pH was readjusted to 7.30, indicating that a NE breakdown product was not responsible for the contraction. These data suggest that adrenergic mechanisms in penetrating cerebral arterioles are significantly different from those seen in peripheral arterioles of similar size.

Animals↗
PubMed1984

Morphology of the constricted arteriolar wall: physiological implications.

Microvessels undergo complex shape changes during constriction that could have profound implications for control of resistance. We exploited in vitro cannulation techniques in combination with electron microscopy to assess the effects of physiological degrees of vasoconstriction on the size and form of the lumen of isolated rat mesenteric arterioles. Photomicrographs of vasoconstricted vessels revealed that the luminal surface is folded and thrown into longitudinal ridges several hundred microns long. These ridges begin to form and encroach on the lumen as the vessel is constricted. Ridge height may increase to 5-10 microns, and as many as 50 ridges were observed around the circumference of a 70-microns vessel. Ridges are comprised of endothelial cells, basal elastic lamina, and portions of the smooth muscle cytoplasm including thick filaments. The ridges are major determinants of the relationships among stress on smooth muscle contractile elements, intraluminal pressure, and luminal diameter. The ridges may also limit the precision of measurement of microvessel diameter in situ since it is not known whether the apex or the base of the ridge is measured under typical conditions of in vivo microscopy. Our findings emphasize the need for additional detailed study of wall morphology to fully understand the regulation of microvessel flow resistance by smooth muscle function.

Animals↗
PubMed1983

Oxygen transport in resting and contracting hamster cremaster muscles: experimental and theoretical microvascular studies.

Intravital microscopy of the superfused cremaster muscle was used to measure the density, diameter, length, hematocrit, red cell velocity, and red cell flux in capillaries of the pentobarbital-anesthetized hamster. Oxygen microelectrodes were used to measure oxygen tension (Po2) at a position 75-100 micrometers deep in the muscle between the venous ends of capillaries and, very importantly, at the superfusate-muscle interface. These parameters were measured in resting and contracting muscles and under three values of superfusate Po2: low (8mm Hg), medium (40 mm Hg), and high (75 mm Hg). These data were complete enough to be useful input parameters in a recently developed mathematical model of oxygen transport in exposed tissue (A. S. Popel, 1981, Math. Biosci. 55, 231-246). The model indicated that with high superfusate Po2, oxygen was supplied to the resting muscle almost exclusively from the superfusate because of the vasoconstriction and reduced blood flow. Oxygen consumption of the resting muscle was estimated to be 0.4 ml O2/100 ml tissue X min, assuming muscle oxygen consumption was uniform and independent of Po2 above 1 mm Hg. The estimated rise in oxygen consumption with exercise was four to eight times resting muscle values, which agrees with previously published data. Also, the model predicted an inlet capillary Po2 of 27 mm Hg with a low superfusate Po2, which is consistent with the few available direct measurements. The model emphasized that with measurement of the Po2 at the superfusate-tissue interface, the complex O2 transport effects of the superfusate can be accurately characterized. Measurement of this and other parameters of the model leads to a potentially useful prediction of the Po2 distribution within tissues under a variety of conditions.

Animals↗
PubMed1983

Capillarity and fiber types in the cremaster muscle of rat and hamster.

We determined muscle fiber type and capillarity in cremaster muscle samples from rats and hamsters of different ages. Histochemical estimation of oxidative capacity was made from the activity of either nicotinamide dinucleotide tetrazolium reductase (NADH-TR) or succinic dehydrogenase (SDH), and fibers were termed fast or slow from myofibrillar ATPase activity. Fibers were classified as type I (low ATPase, high NADH-TR/SDH), type IIa (high ATPase, high SDH/NADH-TR), type IIb (high ATPase, low SDH/NADH-TR), or type IIc (no acid reversal of ATPase, high NADH-TR). Type IIb fibers accounted for 60-80% of the muscle area in both species at all ages. The principal change with maturation was muscle fiber hypertrophy. Mean cross-sectional fiber area increased from 488 +/- 70 (SE) and 453 +/- 19 micron2 in young hamsters and rats, respectively, to 1,255 +/- 99 and 1,540 +/- 101 micron2 in adults. Capillary density (no. of capillaries/mm2 tissue) paralleled fiber hypertrophy; it decreased significantly with maturation from 684 +/- 60 (SE) to 228 +/- 26/mm2 in hamsters and from 341 +/- 15 to 213 +/- 15/mm2 in rats. In vitro estimates of capillary density are compared with previously obtained in vivo data (31), and sources of error are identified. We conclude that reported differences in microvascular function in the cremaster muscle in vivo during maturation or between species cannot be ascribed to changes in muscle composition.

Abdominal Muscles↗
PubMed1983

A computerized system for densitometric analysis of the microcirculation.

An analytical system for measuring size, motion, and light absorption of objects in the field of a microscope is described. The design criteria have been chosen to produce a system that permits acquisition of densitometric information at a number of points within the field and permits computation of important variables from the densitometric data. Relatively simple fiber-optics systems for sampling light intensity at selected locations in the microscope field are described. Computer programs are outlined that permit computation of microvessel diameter, red cell velocity, and hemoglobin oxygen saturation. The sampling systems and programs are quite general in nature and should be applicable to other types of related measurements and computing devices.

Capillaries↗
PubMed1983

Toxic effects of silver-silver chloride electrodes on vascular smooth muscle.

We found that silver, either as silver metal or silver chloride, exerted toxic effects on the smooth muscle of isolated cannulated hamster cheek pouch arterioles. Silver initially stimulated the smooth muscle, producing a marked vasoconstriction. The vessels then dilated back to control diameters. Once the arterioles began to dilate, they became refractory to norepinephrine or potassium stimulation. We caution the use of silver in the presence of smooth muscle, especially when tissue mass is small or free protein concentration is low.

Animals↗
PubMed1983

The oxygen sensitivity of hamster cheek pouch arterioles. In vitro and in situ studies.

We tested the hypothesis that a parenchymally derived mediator is required for arterioles to exhibit oxygen sensitivity. To that end, the parenchyma was dissected and removed from around hamster cheek pouch arterioles, and the oxygen sensitivity of these "aparenchymal arteriolar segments" was studied, either in vitro, after cannulation, or in situ. Arteriolar segments in situ with and without parenchyma had similar oxygen sensitivities (20% constriction as Po2 increased from 15 to 150 mm Hg). Arteriolar occlusion, which eliminated blood flow in the in situ aparenchymal segments, did not eliminate their oxygen sensitivity. The oxygen-induced constriction in the occluded aparenchymal segments was blunted but not eliminated by covering the segments with glass plates to prevent changes in Po2 from occurring around these vessels. We hypothesized that propagation of a portion of the oxygen response might explain the persistent response in the covered and occluded arteriolar segments. Oxygen sensitivity could be shown in only 32% of the in vitro cannulated arterioles (16% mean constriction as Po2 increased from 20 to 150 mm Hg). In contrast, 75% of aparenchymal arterioles were sensitive to changes in Po2 in situ. These data led us to reject the hypothesis that a parenchymally derived mediator is absolutely required for arterioles to exhibit oxygen sensitivity. We infer that the oxygen sensitivity of hamster cheek pouch arterioles results partially or totally from the local action of oxygen on some component of the arteriolar wall or blood, that a portion of the oxygen response may be the result of a propagated phenomenon, and that the oxygen-sensitive component is fragile and is easily lost in preparation for in vitro measurements or in cannulation. It is emphasized that the O2 sensor need not reside in vascular smooth muscle.

Animals↗
PubMed1982

A comparison of microvascular estimates of capillary blood flow with direct measurements of total striated muscle flow.

Relations between bulk flow into skeletal muscles and microscopically observed capillary flow are compared and disagreements between the two types of data are found. Mean capillary blood velocity was computed using data from a variety of literature sources and assuming uniform distribution of flow through a parallel array of capillaries. The average ratio of measured red cell velocity to computed mean blood velocity was 4.4 +/- 1.0. This is statistically different from the measured value reported in the literature of 1.3. In the cremaster muscle, bulk flow of red cells into the tissue was not statistically different from the measured flux of single red cells through capillaries observed microscopically. The factors which contribute to this apparent agreement of mass balance are not understood, however. Capillary hematocrit is very low and the low capillary hematocrit has been explained by others by the presence of nonuniform flow distribution among the capillaries (shunts or flow heterogeneity). However, for the cremaster data sample, red cells were accounted for in observed capillary flow and red cells were distributed rather homogeneously through the capillaries. This suggests that low capillary hematocrit is the result neither of shunting of red cells around the capillaries nor of nonuniform capillary red cell flow alone. There does not appear to be any well-accepted phenomenon which will explain the findings of: 1) low apparent mean blood velocity; 2) low and variable hematocrit; and 3) apparent conservation of red cell mass. The findings can be reconciled, however, if the capillary rheology is more complex than heretofore anticipated, with a stabilized layer of plasma on the inner surface of the capillary in the order of a 1-micrometer thickness. While there is little direct evidence for such a layer at this time, data which are consistent with the possible existence of such a layer are presented.

Animals↗