Large Venules Research Articles

A dynamic nonlinear lumped parameter model for skeletal muscle circulation

A dynamic nonlinear lumped parameter model of the circulation of skeletal muscle for constant vasoactive state is presented. This model consists of four compartments that represent the large arteries, the arterioles, the capillaries and venules, and the veins, respectively. The first compartment consists of a linear compliance (C1) and resistance (R1). The third compartment possesses no compliance and is represented by a linear resistance (R3). The second and fourth compartments each consist of a nonlinear pressure-volume relation, resulting in a pressure dependent compliance (C2, C4, respectively) and nonlinear resistance (R2, R4, respectively). The eleven model parameters were collected in a complementary way: they were partly obtained from a priori knowledge including information at the microscopic level, and partly determined by means of an estimation algorithm. Estimated values of the compliances (in cm3.kPa-1.100 g-1, 1 kPa = 7.5 mmHg) and resistances (in kPa.s.cm-3.100 g) at an (arterial) inflow pressure of 10 kPa and a (venous) outflow pressure of 0 kPa were: C1: 0.014; R1: 6.6; C2: 0.565; R2: 84.6; R3: 37.9; C4: 1.044; R4: 24.5. The model (with the nonlinear pressure-volume relations) is able to predict the static and dynamic instantaneous (i.e., for constant vasomotor tone) pressure-flow relation and the instantaneous zero flow pressure intercept. These phenomena are therefore not necessarily the result of the rheological properties of blood. The secondary or delayed dilatation upon a positive inflow pressure step (or negative step in venous pressure) is predicted by the model implying that delayed dilatation is not necessarily related to changes in vasomotor tone. Venous outflow delay, upon a positive inflow pressure step (starting from zero flow), is also predicted by the model.

Oxygen exchange in the microcirculation of hamster retractor muscle.

We determined percent hemoglobin oxygen saturation (SO2) in arterioles and venules of the hamster retractor muscle at rest. We found that SO2 decreased from 69.9 +/- 1.4% (SE) in large input arterioles (first order, 1A, ID = 60 +/- 3 micron) to flow-weighted values of 56.7% in small arterioles (4A, ID = 20 +/- 1 micron), 51.3% in small venules (4V, ID = 28 +/- 1 micron), and to 50.6 +/- 1.0% in large venules (1V, ID = 147 +/- 13 micron). Thus approximately two-thirds of the net decline in SO2 for this tissue occurred by diffusion of oxygen from arterioles, whereas only about one-third occurred by diffusion from capillaries. Furthermore, no net shunting of oxygen from the arterioles to the venules was detected as evidenced by the absence of any significant change in venular SO2. By determining the SO2 at upstream and downstream ends of arterioles in four consecutive branching orders (1A-4A), we found that the decrease in SO2 per unit length (delta SO2/L) increased approximately 20-fold from 1A to 4A. This increase in delta SO2/L was directly proportional to estimated luminal minus tissue oxygen tension and inversely proportional to red blood cell flow.

Neural degeneration and non-neuronal cellular reactions in the hypoglossal nucleus following an intraneural injection of toxic ricin.

The present study describes neuronal degeneration and its accompanying non-neuronal cellular reaction in the hypoglossal nucleus following an intraneural injection of Ricinus communis agglutinin-60 (RCA-60) into the hypoglossal nerve. The first noticeable structural changes were observed in neurons in hamsters killed 3 days after the RCA injection. Drastic alterations occurred in the period extending from the 5th to the 15th postoperative day. Two forms of neuronal degeneration were observed: light and dark types. In the light type, masses of free ribosomes were observed; other changes included the dilation of Golgi saccules and the presence of abnormal mitochondria. In the dark type of degeneration, the cells became condensed with vacuoles in their cytoplasm. Axon terminals presynaptic to the degenerating cells during this period appeared to be normal. A massive influx of mononuclear leucocytes by diapedesis occurred at the large venules. Some of the infiltrated cells were clearly lymphocytes, while others were monocytes which became indistinguishable from indigenous microglia once they were in the neuropil. Neural macrophages, most probably derived both from microglia and the infiltrated monocytes, were engaged in the phagocytosis of neuronal debris. A remarkable finding in the present study was the wide-spread occurrence of dark axon terminals in the neuropil in longer surviving animals (90 and 120 days). The structural alterations, e.g., clumping and swelling of some of the synaptic vesicles in the enhanced cytoplasmic density, suggest that these were undergoing atrophic changes resulting from the long period of dysfunction following the death of postsynaptic neurons induced by RCA.

Leukocyte phagocytosis and alterations in microvascular integrity elicited by FITC-dextran 150 and epi-illumination in the microcirculation of the hamster cheek pouch

Fluorescein-labeled dextran MW 150K (FITC-Dx 150) is commonly utilized as a macromolecular fluorochrome in inflammatory studies. We examined the influence of FITC-Dx 150 on leukocyte activity as assessed by adherence to cheek pouch microvessels. Transcapillary exchange was evaluated as fluorochrome clearance (Cl). Few leukocytes adhered to the microvascular wall in venous segments prior to and immediately following administration of the dextran fluorochrome. Spontaneous leukocyte adhesion to venous endothelium ensued within 30 min in epi-illuminated, FITC-Dx 150-loaded vessels. However, the Cl of FITC-Dx 150 (1.75 ± 0.68 nl/min) remained unaltered (2.21 ± 1.83 nl/min). Hamsters pretreated with FITC-Dx 150 (a minimum of 7 hr prior to experimentation) and subsequently exposed to epi-illumination showed marked leukocyte adhesion in small venules and an impressive pool of marginating leukocytes in large venules. Leukocyte aggregation, thrombus formation, lymphatic distension, and leukocyte adherence to arteriolar endothelium also ensued as a consequence of epi-illumination. Uptake of FITC-Dx 150 by extravascular phagocytes was evident. Some hamsters pretreated with FITC-Dx 150 developed spontaneous leaky sites upon epifluorescent stimulation. Focal accumulation of interstitial phagocytes was suggestive of fluorochrome uptake and elicitation by FITC-Dx 150. These effects were not observed in control animals treated with FITC-albumin. The results of this study suggest caution in employing FITC-Dx 150 as a permeability probe for studies involving inflammatory processes, especially those dependent on neutrophil/endothelial interactions and prolonged circulation time of fluorochrome.

Neurogenic inflammation in the rat trachea. I. Changes in venules, leucocytes and epithelial cells

This study was done to characterize the morphological changes in the respiratory mucosa that occur in neurogenic inflammation, which is a type of inflammation mediated by substances released from sensory nerves. Neurogenic inflammation was produced in the trachea and bronchi of atropine-treated Long-Evans rats by electrically stimulating the left or right superior laryngeal and vagus nerves. This procedure is known to increase vascular permeability in the airways, presumably as a consequence of antidromic activation of sensory vagal axons (Lundberg & Saria, 1982). By using a particulate tracer (Monastral blue, 30 mg kg-1 i.v.) that does not cross the walls of normal tracheal blood vessels but does cross the endothelium of abnormally permeable vessels, it was possible to identify which blood vessels were affected in neurogenic inflammation. Light and electron microscopic examination of tracheas prepared after 2 or 5 min of vagal stimulation revealed that postcapillary venules and collecting venules 7-80 micron in diameter were labelled by extravasated Monastral blue but capillaries, arterioles, and larger venules were not. Venules from which the extravasation occurred had gaps as wide as 1.5 micron between endothelial cells. Most of the abnormally permeable venules were located just beneath the airway epithelium in regions between the cartilaginous rings. Extravasation also occurred from venules in the mucosa overlying the posterior membrane of the extrathoracic trachea, but little occurred in the posterior membrane of the intrathoracic trachea. After unilateral vagal stimulation, vascular permeability was increased on both sides of the trachea; it was also increased in first through fourth order bronchi but only on the side of stimulation. Leucocytes (principally monocytes and neutrophils) were adherent to the endothelium of some of the abnormally permeable venules. Erythrocytes and platelets also were adherent to the walls of some venules. These changes in venules were accompanied by a degranulation of epithelial secretory cells, widening of the spaces between tracheal epithelial cells, and probably an increase in epithelial permeability. Neurogenic inflammation in the trachea and bronchi of rats is thus characterized by increased permeability of postcapillary venules and collecting venules in specific regions of the respiratory mucosa as well as adherence of leucocytes, erythrocytes and platelets to the endothelium of these venules and prominent changes in the respiratory epithelium.

In vivo determination of the force of leukocyte-endothelium adhesion in the mesenteric microvasculature of the cat.

Quantitative estimates of the force of adhesion between leukocytes and endothelium were obtained from in vivo hemodynamic measurements in small venules of cat mesentery during topical application of the chemotactic compound N-formyl-methionyl-leucyl-phenylalanine (FMLP). Simultaneous measurements of upstream to downstream pressure drop, red cell velocity, microvessel hematocrit, and vessel diameter and length permitted application of the principles of momentum conservation to calculate the forces acting upon a leukocyte during adhesion to the endothelium. For venules ranging in diameter from 23 to 49 micron, the ratio of force (acting in the vessel axial direction) to wall shear stress on the endothelium fell from 14.6 X 10(-6) in small venules to 2.3 X 10(-6) dynes per dyne/cm2 in large venules; reflecting the larger pressure drops and forces attendant to greater lumen obstruction in the smaller venules. The equilibrium force representative of a balance between fluid shear stresses on the leukocyte and those at its site of contact with the endothelium ranged from 1.1 to 76.1 X 10(-5) dynes for wall shear stress ranging from 2 to 25 dynes/cm2; with venules with greater wall shear stresses having the greater leukocyte-endothelium shear force. Within individual venules, however, the force acting on a single leukocyte varied inversely with wall shear stress, most likely due to white blood cell deformation, which leads to a lessening of shear stress on the surface of the white blood cell.

Microvascular effects of atrial natriuretic factor: interaction with alpha 1- and alpha 2-adrenoceptors.

The cremaster skeletal muscle of anesthetized rats was denervated and extended with intact circulation into a tissue bath. Intravital microscopy was used to measure microvessel diameter at three different anatomical levels within the microcirculation: large distributing arterioles (x control diameter = 100 +/- 7 micron), large capacitance venules (147 +/- 8 micron), and small terminal arterioles (17 +/- 1 micron). Norepinephrine (NE) was added to the cremaster bath to produce intermediate reductions in diameter of large arterioles and venules (55% and 38% of maximum constriction, respectively). In the presence of NE tone, bath-added atrial natriuretic factor (ANF) produced concentration-dependent dilation of both arterioles and venules. Arteriolar IC25 = 18 pmol and IC50 = 1.2 X 10(-10) M; venules exhibited similar sensitivity. However, the highest ANF concentration examined (10(-7) M) only reversed NE-induced tone by 70%. In a second large vessel group ANF completely reversed constriction induced by the alpha 1-adrenoceptor agonist, phenylephrine, in the presence of 5 X 10(-7) M yohimbine. However, vessels constricted with the alpha 2-receptor agonist UK-14,304 (in the presence of 10(-8) M prazosin) were insensitive to ANF. A third group of terminal arterioles, which possess considerable spontaneous "intrinsic" tone, were studied in the absence of alpha-receptor agonists. Significant dilation occurred at greater than 10(-7) M, and the maximal response was only 25% of complete dilation with adenosine. These data indicate that ANF exhibits a high potency and selectivity for reversal of alpha 1-adrenoceptor-mediated constriction of large arterioles and venules. Constriction produced by alpha 2-adrenoceptor occupation or by nonadrenergic "intrinsic" mechanisms appears to be insensitive to ANF. We propose that the ability of ANF to reduce microvascular resistance depends on the relative contribution of alpha 1-, alpha 2-, and intrinsic vasoconstrictor components to the prevailing level of smooth muscle tone. Differences in these components among regional circulations and between arterial and venous smooth muscle may contribute to the systemic hemodynamic pattern produced by ANF.

Effect of local tissue cooling on microvascular smooth muscle and postjunctional alpha 2-adrenoceptors.

The effect of local tissue cooling on microvascular smooth muscle contractile behavior and sensitivity to adrenergic constriction was examined in rat cremaster skeletal muscle. Intravital microscopy was used to measure the diameter of first- and second-order arterioles (control diam = 101 +/- 7 microns) and venules (diam = 142 +/- 9 microns), and third-order terminal arterioles (diam = 19 +/- 4 microns). Norepinephrine (NE) was added to the cremaster bath to produce a 20-35% reduction in control diameter obtained at 34 degrees C bath temperature (in situ cremaster temperature). In the presence of NE, cooling the bath to 26 degrees C caused additional constriction of large arterioles and venules. Terminal arterioles exhibited a more pronounced cooling-induced constriction. Spontaneous vasomotion, evident only in this vessel type, was abolished by cooling. Cooling-induced constriction and inhibition of vasomotion were readily reversible with rewarming to 34 degrees C. Blockade of postjunctional alpha 2-adrenoceptors with yohimbine (1-5 X 10(-7) M) completely abolished cooling-induced constriction, as did the alpha 1- and alpha 2-adrenoceptor antagonist phentolamine (10(-6) M); blockade of alpha 1-adrenoceptors with prazosin (10(-8) M) had no effect on the response. After inhibition of the noradrenergic constriction with yohimbine or phentolamine, local cooling dilated terminal arterioles; however, the dilation was transient. These data suggest that modest tissue cooling has a direct, although transient, depressant effect on microvascular smooth muscle tone. However, in the presence of adrenergic constriction, the inhibitory effect of local tissue cooling is overcome by a selective increase in alpha 2- but not alpha 1-mediated vasoconstriction.

Microcirculatory stasis precedes tissue necrosis in ethanol-induced gastric mucosal injury in the rat.

The relation of blood flow stasis to the development of unequivocal histologic necrosis (loss of parietal cells from the column of contiguous cells) in ethanol-induced gastric mucosal injury was studied in anesthetized rats. The most rapid vascular change that occurred when the gastric mucosa was exposed to 100% ethanol was a severe segmental constriction of the large submucosal venules. At 22 sec, the average venular diameter was 52.2 +/- 6.0% of the original one. This was followed by complete superficial mucosal blood flow stasis at 49 +/- 4 sec and appearance of histologic evidence of necrosis in one of seven rats at 2.5 min, four of six rats at 10 min, and seven of seven rats at 60 min. We conclude that in ethanol-induced gastric mucosal injury, submucosal venular constriction occurs first, followed by cessation of mucosal blood flow to be followed later on with histologic evidence of necrosis.

Microcirculatory hematocrit and blood flow

Direct measurements from many laboratories indicate that the oxygen tension in skeletal muscle is significantly less than in the large veins draining these tissues. Harris (1986) has proposed that because of the parallel anatomic arrangement of large arterioles and venules in skeletal muscle, a counter-current exchange between these vessels can occur. He theorized that diffusion of O2 between arteriole and venule would lower the PO2 in the blood as it enters capillaries and result in a decreased tissue PO2 and an increase in large vein PO2. Calculations (Appendix) show that the amount of O2 transferred between arteriole and venule is inadequate to account for this difference in PO2 between tissue and veins due to the small surface area that is involved. It is well documented that the microcirculatory hematocrit ranges between 20 and 50% of that in the supply vessels. The reduced hematocrit lowers the oxygen content in these vessels and results in a low oxygen tension in the surrounding tissue. True arteriovenous shunts are not present in most skeletal muscles, but 15-20% of the microvessels represent thoroughfare or preferential flow channels. It is suggested that these vessels contain a greater than normal hematocrit to account for a conservation of red cell mass across the microcirculation. Furthermore, it is shown that the hematocrit in the preferential flow channels is an inverse function of the flow rate for any level of the microcirculatory hematocrit. The increased hematocrit raises the flow resistance in these vessels which reduces flow further and represents a positive feedback condition which may contribute to the intermittent and uneven flow patterns which are present within the microcirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

In situ analysis of alpha-adrenoceptors on arteriolar and venular smooth muscle in rat skeletal muscle microcirculation.

The purpose of this study was to determine whether both alpha 1- and alpha 2-adrenergic receptors exist on vascular smooth muscle of microvessels and whether adrenergic constriction of anatomically distinct microvascular segments is differentially subserved by either receptor subtype. The cremaster skeletal muscle of anesthetized rats was acutely denervated and suspended in a Krebs bath containing cocaine, normetanephrine, and propranolol to block uptake1, uptake2, and beta-receptors, respectively. Intravital microscopy was used to study large distributing arterioles (mean diameter, 100 microns), small precapillary arterioles (25 microns), and capacitance venules (140 microns). Concentration-response (diameter change) curves were obtained for bath-added agonists norepinephrine (mixed alpha 1/alpha 2), phenylephrine (alpha 1), and B-HT 933 (alpha 2) in the absence or presence of antagonists prazosin (alpha 1) and yohimbine (alpha 2). Apparent pD2(-log ED50) values for large arterioles and venules were, respectively, as follows: norepinephrine (7.41 and 7.15), phenylephrine (5.95 and 5.41), and B-HT 933 (5.05 and 5.06). Low concentrations of prazosin (10(-8) M) and yohimbine (10(-7) M) produced receptor subtype-selective antagonism and parallel, dextral displacement of norepinephrine curves for large arterioles and venules. The large arteriole pKB (-log KB) was 7.83 +/- 0.65 for prazosin and 7.36 +/- 0.46 for yohimbine. Higher concentrations of prazosin (10(-7) and 3 X 10(-7) M) and yohimbine (10(-6) M) produced further dextral but nonparallel displacement of norepinephrine curves. In contrast, receptor subtype-selective concentrations of only yohimbine inhibited adrenergic constriction of small, precapillary arterioles; but prazosin had no effect at receptor subtype-selective concentrations. These data suggest that adrenergic regulation of large arterioles and venules in skeletal muscle uses both alpha 1- and alpha 2-adrenoceptors. Precapillary arterioles, however, may be subserved predominantly by alpha 2-receptors.

Leukocyte endothelium adhesion and microvascular hemodynamics.

In the present study we have attempted to provide quantitative details of hemodynamic determinants of leukocyte to endothelium adhesion in the microvasculature. To this end, several hypotheses have been advanced to suggest that the preferential adhesion of leukocytes in the larger venules (30-50 microns diameter) rests upon the inherent ability of the microvasculature to compensate for small perturbations in resistance and that WBC deformability may play a significant role in this process. Flow redistribution and attendant arteriolar vasomotor adjustments may forestall LEA in the larger collecting venules of the network, where venous obstruction may be countered by bringing the full weight of the arteriovenous pressure gradient to oppose WBC adhesion. Direct measurements of the force of adhesion suggest that with diminishing vessel diameter, as for example in the immediate post-capillary venules, WBC dispersal forces will be greatest due to dramatic increases in the proportionality between force and wall shear stress. This event would tend to preclude adhesion in the smallest venular microvessels. It has also been shown that there is a strong potential for WBC deformability to affect the adhesion process by modification of the shear stresses acting on the WBC surface, as evidenced by an inverse relationship between force and wall shear stress and direct observations of WBC shape changes with increasing shear.

Microvascular pressure in venules of skeletal muscle during arterial pressure reduction.

It has been suggested from whole organ studies that the viscosity of blood in skeletal muscle venules varies inversely with flow over physiological flow ranges. If this is the case, the hydrostatic pressure gradient in venules should change less than flow as flow is altered. To test this hypothesis, pressure in venules of cat sartorius muscle was measured during stepwise arterial pressure reduction to 20 mmHg. Large vein pressure remained constant at about 5 mmHg. Average pressures in the large venules (40-185 microns) ranged from 13.6 to 10.0 mmHg. The difference between pressure in these venules and large vein pressure fell in proportion to the reduction in blood pressure and blood flow. Pressures in the smallest venules studied (25 microns) averaged 19.7 +/- 6.2 (SD) mmHg. The pressure difference between the smallest venules and the large vein fell less than the arteriovenous pressure difference or blood flow when arterial pressure was reduced. During reactive hyperemia the pressure gradient between the smallest venules and the large vein rose proportionately less than blood flow. The stability of pressure in the smallest venules is consistent with the hypothesis that blood viscosity varies inversely with flow rate.

In vivo venular changes with the development of one-kidney, one-clip hypertension in the rat.

Television microscopy was used to quantify in vivo resting venular diameters and the responses to topically applied norepinephrine in the cremaster muscle of two groups of urethanchloralose anesthetized rats: normotensive rats (NT) and one-kidney, one-clip Goldblatt hypertensive rats (1K1C). Observations were made two weeks after the surgery which was used to induce renovascular hypertension. At this stage, we have previously observed an increase in arteriolar reactivity (1). In the current study, mean arterial blood pressures for 1K1C (149 +/- 5 mmHg) were significantly higher than pressures for NT (102 +/- 3 mmHg). Venules were categorized by branching order and venular diameters were measured at three different levels of the microcirculation: first (1V), second (2V), and third order (3V) venules. Reactivity to norepinephrine at all venular levels in the 1K1C group was similar to that recorded for the NT group. Resting venular luminal diameters, however, were significantly smaller (20%) for large (1V) venules of the HT group (137 +/- 9 micron) compared to those for the NT group (171 +/- 10 micron). Thus, in contrast to previously reported data for arterioles, a structural venoconstriction and not an increase in venular reactivity appears to characterize the early vascular changes associated with this form of renovascular hypertension.

In Vivo Observation of the Lymphatic System in the Rat Stomach

The anatomy of the lymphatic system in the rat stomach was studied by means of fluorescent in vivo microscopy. A fluorescein-albumin conjugate was injected via a micropipette into the mucosa, submucosa, or muscularis externa. The movement of the conjugate was visualized using a closed-circuit television system. When injected into the base of the mucosa, the conjugate was seen to flow from the deposited pool. These fluorescent streams, 21-53 micron in diameter, formed a network in the base of the mucosa and superficial submucosa. They were in close approximation to, but separate from, the arterioles and venules. These fluorescent channels are probably lymphatic microvessels, as they were connected to larger lymphatic vessels running parallel to the large arterioles and venules in the deep submucosa. These larger lymphatic vessels passed through the muscularis externa and drained into extragastric lymphatic vessels on the lesser or greater curvature. There was no network of lymphatic microvessels in the deep submucosa or muscularis externa. The extragastric lymphatic vessels, 50-340 micron in diameter, had valves and displayed spontaneous contractions, moving the conjugate toward the lymph nodes.

The effects of intrauterine contraceptive devices on the ultrastructure of the endometrium in relation to bleeding complications

The effects of inert (Lippes Loop D and Dalkon Shields) and medicated (copper 7, copper T, and Progestasert) intrauterine contraceptive devices (IUDs) on the ultrastructure of the endometrium were studied in intact human uteri. The most striking morphologic changes induced by the inert and copper-bearing devices were erosion of the surface epithelium and extensive microthrombosis in stromal capillaries of the endometrium in contact with the device. These abnormalities were associated with extravascular thrombi, erythrocytes, and fibrin deposition in the adjacent stroma. Capillary microthrombosis and leukocyte infiltration into the uterine cavity were most extensive around the active part of the copper-bearing devices. With the Progestasert erosion of surface epithelium was rarely seen, but the intact epithelial lining had fewer ciliated cells with flattened and shortened cilia. Large dilated venules were a common finding below the surface epithelium adjacent to the active part of the Progestasert; capillary microthrombosis was found only below the inert arms of the Progestasert. The vascular response of the endometrium to IUDs appears, therefore, to be directly related to the type and proximity of the device. The morphologic changes induced in both surface epithelium and the microvasculature of the endometrium are the likely explanation of the uterine bleeding problems associated with IUDs but are probably intrinsic to the mode of action of the IUD in interfering with implantation.

Fallopian tube microvasculature in the rabbit.

The microvascular architecture of rabbit Fallopian tube isthmic, ampullary and fimbrial regions was examined by the corrosion vascular cast-scanning electron microscope method. The aorta and inferior vena cava of virgin adult female rabbits (2.5-3.5 kg) were cannulated; after blood wash out, methacrylate casting medium was infused via the aorta. After plastic hardening, Fallopian tubes were excised, tissues corroded and casts prepared for scanning electron microscopy. The isthmic myosalpinx is encircled subserosally by an interlocking venous plexus. We suggest that a rise in pelvic venous pressure could lead to a decrease in isthmic luminal diameter and thus act as a sphincter contributing to the known delay in ovum transport at the ampullary isthmic junction. Stereo pairs of photomicrographs showed that isthmic plicae are supplied by arterioles which change little in diameter passing through the tubal wall. Near the apex of a fold, these arterioles terminate in a subepithelial capillary plexus which drains to deep mucosal and plical core venules. In contrast, the ampulla is supplied by smaller and less frequent arterioles. Frequent large venules extending high into the plicae drain the subepithelial capillary plexus. Based on this microvascular architecture, we suggest that the subepithelial capillary plexus of the apical region of the plicae probably contains high pressure blood in the isthmus and lower pressure blood in the ampulla. Therefore, plicae in these regions may be specialised for net luminal fluid secretion and absorption respectively, implying a role for the microvasculature in tubal transport by initiation or modification of fluid flow along the lumen.

Increase in vascular permeability induced by leukotriene B4 and the role of polymorphonuclear leukocytes.

Leukotriene B4 (LTB4), a metabolite of arachidonic acid, is known to be a potent chemotactic and chemokinetic substance. We have used the hamster cheek pouch microcirculation model to study the effect of LTB4 on vascular permeability and the involvement of neutrophil granulocytes in this response. Intravascular fluorescein-labeled dextran (mol wt 150,000) was used as a tracer of macromolecular permeability. Topical application of LTB4 (150 nM-5 microM) to the hamster cheek pouch resulted in an immediate increase in adhering leukocytes in postcapillary venules and later venules. Leukocyte accumulation was reversible, but continued longer the higher the dose of LTB4 used. Subsequently, a dose-dependent increase in vascular permeability was seen at post-capillary and larger venules, with a maximum 10-20 min after application; the maximum occurred later the higher the dose of LTB4. Depletion of neutrophil granulocytes by pretreatment of the animals with antineutrophil serum obtained from immunized rabbits significantly decreased the permeability response to LTB4, whereas the response to histamine was unaffected. These results suggest that neutrophil granulocytes play a role in LTB4-mediated permeability increase. LTB4 may be of importance both for the leukocyte accumulation and for the edema formation seen in inflammatory reactions.

Quantification of the adhesion of platelets in hamster venules in vivo.

(i) Citrated platelet-rich plasma freshly prepared from golden hamsters was mixed with fluorescein isothiocyanate (FITC) which made the platelets fluorescent. These platelets were injected intravenously into anaesthetized hamsters with exteriorized cheek pouch preparations superfused at 37 °C with Krebs-bicarbonate solution. The exposed microcirculation was observed microscopically by bright field or fluores­cent illumination. The flowing and sticking of fluorescent platelets was recorded on video tape for quantitative analysis. (ii) In four experiments 22–36%, mean 28%, of fluorescent platelets were circulating 2-3 h after their injection. In seven experiments the fluorescent platelets accounted for 0.6–3.3 %, mean 1.7 %, of circulating platelets. (iii) In venules 20–60 μm in diameter small proportions, mean 5.4%, of circulating fluorescent platelets stopped moving by sticking to the vessel walls. About 80 % of these platelets stuck for up to 1 s, a further 10-15% for up to 5 s, and only about 2% for longer than 2 min. There was an inverse relation between size of venule and proportion of platelets sticking in them. (iv) There was a direct relation between the mean velocities at which platelets flowed through the venules and the sizes of the venules. In the smaller venules the velocity distribution of the platelets had a clear maximum which was not as evident in larger venules. (v) In a few observations on arterioles, flowing platelets could not be seen, and arrested platelets only in a dilatation and at a capillary branch. (vi) Ethylenediamine tetraacetate in the superfusing fluid decreased platelet sticking in venules but did not abolish it. (vii) Adenosine diphosphate in the superfusing fluid caused the appear­ance of platelet aggregates in venules and of sticking platelets in arterioles during progressive diminution in blood flow through both types of vessel. (viii) The observations make it improbable that the release of platelet constituents affects normal venules or arterioles except, possibly, where haemodynamic conditions are affected by wall irregularities such as dilations or branching.

The effect of the progesterone-releasing intrauterine device on uterine endometrium and fallopian tube epithelium.

A scanning and transmission electron microscopy study was undertaken of the effect of the progesterone releasing intrauterine device (Progestasert, Alza Corporation, USA) on the uterine endometrium and fallopian tube epithelium. Small erosions of surface epithelium and microthrombosis of stromal capillaries were found in the endometrium below the inert part of the device. A reduction of ciliated cells and shortened cilia were seen in the endometrium below the active part of the device and large dilated venules were present in the underlying stroma. Fallopian tubes from IUD patients contained fewer ciliated cells than those of the controls. The morphological changes described are likely to be major factors responsible for the irregular bleeding which occurs with Progestasert IUDs and the possible increase in tubal pregnancy.