Structural characteristics of the mammalian spleen indicating storage and release of red blood cells. Aspects of evolutionary and environmental demands

Size-Dependent In Vivo Transport of Nanoparticles: Implications for Delivery, Targeting, and Clearance

Understanding the in vivo transport of nanoparticles provides guidelines for designing nanomedicines with higher efficacy and fewer side effects. Among many factors, the size of nanoparticles plays a key role in controlling their in vivo transport behaviors due to the existence of various physiological size thresholds within the body and size-dependent nano-bio interactions. Encouraged by the evolving discoveries of nanoparticle-size-dependent biological effects, we believe that it is necessary to systematically summarize the size-scaling laws of nanoparticle transport in vivo. In this review, we summarized the size effect of nanoparticles on their in vivo transport along their journey in the body: begin with the administration of nanoparticles via different delivery routes, followed by the targeting of nanoparticles to intended tissues including tumors and other organs, and eventually clearance of nanoparticles through the liver or kidneys. We outlined the tools for investigating the in vivo transport of nanoparticles as well. Finally, we discussed how we may leverage the size-dependent transport to tackle some of the key challenges in nanomedicine translation and also raised important size-related questions that remain to be answered in the future.

Structure of the Eurasian moorhen spleen: A comprehensive study using gross anatomy, light, and transmission electron microscopy

The spleen is the largest secondary lymphoid organ with major roles in the removal of blood-borne antigens. The Eurasian moorhen is a wild aquatic bird that revealed the adaptation to harsh environmental conditions. Information regarding the structural features of moorhen's spleen is lacking. The present study aimed to describe the composition of moorhen's spleen using anatomical dissection, histology, histochemistry, immunohistochemistry, and transmission electron microscopy. The spleen appeared as a brownish red sickle-shaped organ close to the proventriculus and gizzard. The splenic capsule was very thin, and the trabeculae were poorly developed. The white pulp formed of the periarteriolar lymphoid sheath, lymphoid follicles, and periellipsoidal lymphatic sheath. The red pulp composed of sinusoids and cords and contained various types of blood cells. Blood vessels were observed within the splenic capsule and inside the parenchyma. Notably, penicillar capillaries (PCs) appeared branched and surrounded by well-developed ellipsoids. Direct connections were observed between PCs and splenic sinusoids suggesting a closed type of circulation. Ultrastructurally, intercellular spaces and vascular channels were evident in the wall of PCs. Ellipsoid-associated cells, lymphocytes, monocytes, and heterophils were observed within splenic ellipsoids. Ellipsoids were thus suggested as a crucial component of moorhen's spleen. Numerous MafB-immunoreactive (IR) macrophages were seen within the red pulp. Splenic cords contained the highest number of PHH3-IR cells, while CCASP3-IR cells were exclusive to follicles of the white pulp. In conclusion, the structure of moorhen's spleen revealed species-specific features. The findings of the present study could help to improve the immunity of domestic birds.

Architecture and Cellular Composition of the Spleen in the Japanese Quail (Coturnix japonica)

The spleen is considered a key player in birds' immunity. The stroma and the parenchyma of the spleen of the adult quail were demonstrated histologically, histochemically, and ultrastructurally. A thin capsule and the absence of trabeculae were the most characteristics of spleen stroma. The demarcation between white pulp and red pulp was not observed in the quail. White pulp formed from the periarterial lymphatic sheath and the periellipsoidal lymphatic sheath, both of which were surrounded by arteriole and ellipsoid, respectively. Ellipsoids appeared more numerous and were characterized by cuboidal lining of the epithelium and supporting cells. Red pulp consisted of sinuses and cords. White pulp and red pulp of the quail spleen contained various cells, such as red blood cells, macrophages, heterophils with characteristic granules, lymphocytes of different sizes, dendritic cells, plasma cells, and telocytes. In addition, closed circulation and open circulation established the blood flow on the spleen.

Phenylephrine use for blood sparing during splenectomy in a dog

A dog with immune-mediated haemolytic anaemia was presented for splenectomy. Phenylephrine administration immediately before the removal of the spleen induced splenic contraction and significantly elevated packed cell volume. This technique conserved red blood cells and may be beneficial in euvolaemic animals to reduce the likelihood of a transfusion being required in the event of surgical haemorrhage.

Immunological Insights into the Life and Times of the Extinct Tasmanian Tiger (Thylacinus cynocephalus)

The thylacine (Thylacinus cynocephalus) was Australia’s largest marsupial carnivore until its extinction within the last century. There remains considerable interest and debate regarding the biology of this species. Studies of thylacine biology are now limited to preserved specimens, and parts thereof, as well as written historical accounts of its biology. This study describes the development of the immune tissues of a pouch young thylacine, one of only eleven in existence, and the only specimen to be histologically sectioned. The appearance of the immune tissue of the developing pouch young thylacine is compared to the immune tissues of extant marsupials, providing insights into the immunity, biology and ecology of the extinct thylacine.

Pumpless extracorporeal CO(2) removal restores normocapnia and is associated with less regional perfusion in experimental acute lung injury

BACKGROUND

Lung protective ventilation may lead to hypoventilation with subsequent hypercapnic acidosis (HA). If HA cannot be tolerated or occurs despite increasing respiratory rate or buffering, extracorporeal CO2-removal using a percutaneous extracorporeal lung assist (pECLA) is an option. We hypothesised that compensation of HA using pECLA impairs regional perfusion. To test this hypothesis we determined organ blood flows in a lung-injury model with combined hypercapnic and metabolic acidosis.

METHODS

After induction of lung injury using hydrochloric acid (HCl) aspiration and metabolic acidosis by intravenous HCl infusion in nine pigs, an arterial-venous pECLA device was inserted. In randomised order, four treatments were tested: pECLA shunt (1) with and (2) without HA, and clamped pECLA shunt (3) with and (4) without HA. Regional blood flows were measured with the coloured microsphere technique.

RESULTS

HA resulted in higher perfusion in adrenal glands, spleen and parts of splanchnic area (P < 0.05) compared with normocapnia. During CO2-removal with pECLA, regional perfusion decreased to levels comparable with those without pECLA and normocapnia. Cardiac output (CO) increased during HA without a pECLA shunt and was highest during HA with a pECLA shunt compared with normocapnia. During CO2-removal with pECLA, this variable decreased but stayed higher than during normocapnia with clamped pECLA shunt (P < 0.05).

CONCLUSION

In our lung-injury model, HA was associated with increased systemic and regional blood flow in several organs. pECLA provides effective CO2 removal, requiring a higher CO for perfusion of the pECLA device without improvement of regional organ perfusion.

Splenectomy increases mortality in murine Trypanosoma cruzi infection

The spleen is a secondary lymphoid organ that harbours a variety of cells such as T and B lymphocytes and antigen-presenting cells important to immune response development. In this study, we evaluated the impact of spleen removal in the immune response to experimental Trypanosoma cruzi infection. C57BL/6 mice were infected with Y strain of the parasite and infection was followed daily. Mice that underwent splenectomy had fewer parasites in peripheral blood at the peak of infection; however, mortality was increased. Histological analysis of heart and liver tissues revealed an increased number of parasites and inflammatory infiltrates at these sites. Spleen removal was associated with reduction in IFN-γ and TNF-α production during infection as well as with a decrease in specific antibody secretion. Haematological disorders were also detected. Splenectomized mice exhibited severe anaemia and decreased bone marrow cell numbers. Our results indicate that spleen integrity is critical in T. cruzi infection for the immune response against the parasite, as well as for the control of bone marrow haematological function.

Oxygent as a top load to colloid and hyperoxia is more effective in resuscitation from hemorrhagic shock than colloid and hyperoxia alone

Perfluorocarbon (PFC) emulsions are intravascular oxygen therapeutics that temporarily enhance tissue oxygenation in dilutional anemia. However, PFC emulsions are not resuscitation fluids because PFCs only work optimally in the presence of high O2 partial pressure (hyperoxia); moreover, because they have no oncotic potential, dosing limitations prevent their use to permanently replace large hemorrhage volumes. Our objective was to clarify whether in the presence of hyperoxia a conventional colloid therapy supplemented by PFC is more efficacious than colloid alone. To answer this question, 22 anesthetized, ventilated dogs were hemorrhaged to a mean arterial pressure of 45 mmHg and were kept at this level until a metabolic O2 debt of 120 mL kg(-1) body weight had evolved. Hyperoxia was established and dogs were randomly allocated to receive colloid (6% HES, Hydroxy Ethyl Starch shed blood volume) or colloid together with Oxygent (perflubron emulsion, 60%, w/v; Alliance Pharmaceutical Corp., San Diego, CA; single dose, 4.5 mL kg(-1); i.e., 2.7 g PFC kg body weight) in a blinded fashion. Hemodynamic and O2 transport parameters, intestinal mucosal blood flow (microspheres), and O2 partial pressure (MDO-Electrode; Eschweiler, Kiel, Germany) were measured at baseline, in shock, and during 3 h post-therapy. In the presence of hyperoxia, Oxygent improved the amount of physically dissolved O2 in plasma and increased the contribution of physically dissolved O2 to global O2 delivery (P < 0.05) and thus whole body O2 consumption when compared with colloid alone (P < 0.05). As a result, Oxygent reduced intestinal mucosal hypoxia and global O2 debt within the first hour post-therapy (P < 0.05). We conclude that under hyperoxic conditions, fluid resuscitation supplemented by Oxygent was more efficacious than colloid and hyperoxia alone. PFC temporarily enhanced intestinal mucosal tissue oxygenation during resuscitation.

Bowhunting deer

There are conflicting views about the humaneness of the handbow as a recreational hunting method for deer. Some claim that it is the most humane hunting method, whilst others report higher wounding rates and crippling losses than with the rifle. This commentary summarises the factors affecting the likelihood of a quick death, the types of equipment commonly used, the vital target areas, the influence of blood loss on blood pressure and brain function and the prevalence of wounding during routine bowhunting. Some requirements in Bowhunters Association Codes of Conduct are also described. It is concluded that where bowhunting is allowed, Codes of Conduct should emphasise the hunters' responsibility to track and despatch injured animals, and adherence to the Codes should be encouraged, if not enforced.

Can we continue research in splenectomized dogs? Mycoplasma haemocanis: old problem--new insight

We report the appearance of a Mycoplasma haemocanis infection in laboratory dogs, which has been reported previously, yet, never before in Europe. Outbreak of the disease was triggered by a splenectomy intended to prepare the dogs for a hemorrhagic shock study. The clinical course of the dogs was dramatic including anorexia and hemolytic anemia. Treatment included allogeneic transfusion, prednisone, and oxytetracycline. Systematic follow-up (n = 12, blood smears, antibody testing and specific polymerase chain reaction) gives clear evidence that persistent eradication of M. haemocanis is unlikely. We, therefore, had to abandon the intended shock study. In the absence of effective surveillance and screening for M. haemocanis, the question arises whether it is prudent to continue shock research in splenectomized dogs.

The spleen of Zaedyus pichiy, (Mammalia, Dasypodidae): a light and electron microscopic study

Armadillos are ancient mammals important as models for biomedical, evolutive and ecological studies, because they have adaptive and primitive morpho-physiological characteristics. In this work we study the splenic microarchitecture of the 'Patagonian Piche', Zaedyus pichiy, as an attempt to understand the relationship between the organizational plan of the organ and the particular features of this species. The organ samples were classically processed for light and electron microscopic study. The microanatomy of the organ as well as its different cell types are studied. The spleen is non-sinusoidal, with the typical arrangement for storage functions. White pulp is well defined. Red pulp is a meshwork of circulating, immunocompetent and haemopoietic cells. The general structure of the organ agrees with the semi-fossorial habit and the adaptability of the species. Comparative aspects with other armadillos or other less specialized groups are discussed. Persistence of haemopoietic spleen activity in the adult suggests the existence of specific inductive functions of the stroma. Better knowledge of spleen structure and function in ancient mammals may give important information about their phylogeny.

Retinal venous oxygen saturation and cardiac output during controlled hemorrhage and resuscitation

The objective was to test calibration of an eye oximeter (EOX) in a vitiligo swine eye and correlate retinal venous oxygen saturation (Srv(O(2))), mixed venous oxygen saturation (Sv(O(2))), and cardiac output (CO) during robust changes in blood volume. Ten anesthetized adult Sinclair swine with retinal vitiligo were placed on stepwise decreasing amounts of oxygen. At each oxygen level, femoral artery oxygen saturation (Sa(O(2))) and retinal artery oxygen saturation (Sra(O(2))) were obtained. After equilibration on 100% O(2), subjects were bled at 1.4 ml. kg(-1). min(-1) for 20 min. Subsequently, anticoagulated shed blood was reinfused at the same rate. During graded hypoxia, exsanguination, and reinfusion, Sra(O(2)) and Srv(O(2)) were measured by using the EOX, and CO and Sv(O(2)) were measured by using a pulmonary artery catheter. During graded hypoxia, Sra(O(2)) correlated with Sa(O(2)) (r = 0.92). Srv(O(2)) correlated with Sv(O(2)) (r = 0.89) during exsanguination and reinfusion. Sv(O(2)) and Srv(O(2)) correlated with CO during blood removal and resuscitation (r = 0.92). Use of vitiligo retinas improved the calibration of EOX measurements. In this robust hemorrhage model, Srv(O(2)) correlates with CO and Sv(O(2)) across the range of exsanguination and resuscitation.

Uneven changes in circulating blood cell counts with adrenergic stimulation to the canine spleen

1. Responses of splenic diameter measured by sonomicrometry to alpha- and beta-adrenoceptor stimulants were estimated together with simultaneously measured systemic arterial and splenic venous concentrations of red blood cells (RBC), white blood cells (WBC) and platelets (PLT) in anaesthetized dogs. 2. Intravenous and intrasplenic arterial injections of adrenaline, noradrenaline and phenylephrine all produced profound decreases in splenic diameter. Increases in systemic arterial concentrations of RBC produced by these stimulants were observed immediately following the splenic contraction and marked increases in splenic venous concentration of RBC. 3. Adrenaline and noradrenaline both caused rapid and transient decreases in WBC release from the spleen and these agonists then, in addition to phenylephrine, caused gradual and small increases in systemic arterial WBC concentrations. The increases in arterial RBC and WBC concentrations were abolished by transient isolation of the spleen from the systemic circulation. These three agents did not significantly modify differences between splenic venous and systemic arterial concentrations of PLT. 4. Intra-arterial injections of isoprenaline caused an increase in splenic diameter and a significant decrease in the splenic venous concentration of WBC, but barely influenced the veno-arterial differences in RBC and PLT concentrations across the spleen. 5. The present results indicate that contraction of the spleen through stimulation of splenic alpha1-adrenoceptors contributes to supplying RBC but not PLT into the systemic circulation, whereas splenic beta-adrenoceptor activation leads to splenic dilatation with increased sequestration of WBC to the spleen despite no changes in the release of RBC and PLT from the spleen.

A role for parathyroid hormone-related protein in the pathogenesis of inflammatory/autoimmune diseases

Our increased understanding of the critical role of cytokines in chronic inflammatory/autoimmune diseases has led to the recent development of effective anti-cytokine treatments. In particular, agents blocking the function of TNF-alpha, a cytokine first identified as an endotoxin-inducible mediator of tumor cell necrosis, are now licensed for the treatment of rheumatoid arthritis (RA) and inflammatory bowel disease. However, TNF-alpha is but one member of a cytokine network that is responsible for mediating these inflammatory disorders. Therefore, as our understanding of the pathophysiologic role of other members of this inflammatory network increases, other cytokines may similarly be identified as effective targets for treatment. In this article, we will review evidence which suggests that parathyroid hormone-related protein (PTHrP), a peptide which, like TNF-alpha, was first identified because of its effects in the setting of malignancy, may in fact serve an important non-neoplastic, physiologic function by mediating the inflammatory/autoimmune host response. Data identifying PTHrP as a member of the cytokine network induced in multi-organ inflammation and rheumatoid arthritis will be summarized, initial evidence comparing the therapeutic efficacy of PTHrP- vs. TNF-alpha-blockade in the treatment of endotoxemia will be reviewed, and potential future areas of research, including assessment of the effects of PTHrP blockade in the treatment of RA, will be discussed.

alpha2-Adrenergic-receptor response in reversible increase in hemoglobin concentration in intermittent hypoxia

We have previously shown that intermittent hypoxia (IHx, 10% O(2), 60 min/day) leads to an increase in the splenic alpha2-adrenoceptor response and results in a splenic contraction-induced reversible increase in hemoglobin concentration ([Hb]). In the present study, we determined whether IHx of shorter duration (15 min/day (15-min) and 30 min/day (30-min)), produced this phenomenon in rats. A significant increase in [Hb] during hypoxia was observed in both the groups, but its magnitude was larger in the 30-min IHx rats. Even when the cumulative exposure time (time/dayxdays) was shorter, the [Hb] increase was larger in the rats with longer daily hypoxic exposure. The alpha2-adrenoceptor antagonist yohimbine abolished the [Hb] increase of 15- and 30-min IHx. The increase in [Hb] following administration of the alpha2-adrenoceptor agonist oxymetazoline was also higher in 30-min IHx; indicating that the higher [Hb] produced by longer daily hypoxic exposure times is the result of increases in alpha2-adrenergic-receptor response of greater magnitude. In conclusion, IHx for periods as short as 15 and 30 min/day increases the splenic alpha2-adrenoceptor response and its magnitude reaches the maximum value depending on the daily hypoxic exposure time. A reversible increase in [Hb] constitutes a useful mechanism that protects organ oxygen supply during hypoxic episodes of variable duration and intensity.

Spleen of Dasypus hybridus (Mammalia, dasypodidae): a light and electron microscopic study

Armadillos are relictual mammals important as models for biomedical studies. They contain adaptative and primitive characteristics in both anatomical and physiological aspects. In this study we describe the splenic histology and cytology of the "mulita," Dasypus hybridus. Organ samples were processed for light and electron microscopy study. The microanatomy of the organ samples as well as their different cell types are described. The spleen is non-sinusoidal, with the typical arrangement for storage functions. White pulp is lightly diffuse. Red pulp is a meshwork of circulating, immunocompetent and hemopoietic cells. Differences with other studied members of the group are discussed. The general structure of the organ agrees with the semi-fossorial habit of the species. Persistence of myeloid activity in the adult suggests the existence of specific inductive functions of the stroma. Better knowledge of this fact may give further insight on the phylogeny of hemopoiesis.

Effect of the method of capture on the haematology and blood chemistry of red deer (Cervus elaphus)

Haematological and plasma biochemical constituents can be affected during capture and handling operations in wildlife. The present study compares the blood constituents of 40 red deer (Cervus elaphus) captured using two different methods: 20 were captured by physical means, using long nets and box traps, and 20 by chemical means, using a mixture of xylazine and ketamine. Significant differences were found in the haemogram: red blood cell count, packed cell volume, haemoglobin concentration, and segmented neutrophil, lymphocyte, monocyte and total leukocyte counts were higher in animals captured by physical means. Conversely, the eosinophil count was higher in deer captured using anaesthetic. The plasma activity of alanine amino transferase, and the concentrations of cholesterol, triglycerides, albumin, alpha-2 globulins, total proteins, sodium and chloride, were significantly higher in the group captured by physical means. With the exception of the eosinophil count, all the blood constituents which presented higher values were in the group of physically captured deer, and thus it is necessary to take into account the method of capture when interpretation or establishment of reference values is performed.

Splenic contraction-induced reversible increase in hemoglobin concentration in intermittent hypoxia

The effect of intermittent hypoxia (IHx) on blood hemoglobin concentration ([Hb]) and the underlying mechanisms were studied in rats exposed to 10% O2, 1 h/day, for up to 5 wk. IHx protocols with longer daily hypoxic exposure show persistent polycythemia; however, it is unknown whether [Hb] increases transiently during hypoxia in protocols without polycythemia. Hypoxia produced a reversible [Hb] increase after 4 days of IHx but not in normoxic controls (NxC) or after shorter period of IHx. Splenectomy abolished the phenomenon. Plasma epinephrine and norepinephrine levels during hypoxia were comparable in IHx and NxC groups, but the epinephrine-induced [Hb] increase was larger in IHx. The alpha1- and alpha2-adrenoreceptor blockade (phentolamine) and alpha2-blockade (yohimbine) abolished the [Hb] increase of IHx rats. Conversely, alpha2-receptor stimulation (oxymetazoline) increased [Hb] during normoxia in IHx but not in NxC. In conclusion, this IHx protocol results in reversible [Hb] increases during hypoxia via splenic contraction mediated by increased alpha2-adrenoreceptor response. This may protect O2 supply during hypoxia without the cardiovascular burden of polycythemia during normoxia.

Retinal large vessel oxygen saturations correlate with early blood loss and hypoxia in anesthetized swine

BACKGROUND

Noninvasive monitoring would likely improve trauma care. Using laser technology, we monitored the oxygen saturation in retinal vessels during exsanguination and hypoxia.

METHODS

Seven anesthetized swine were bled at 0.4 mL/kg/min for 40 minutes. During exsanguination, retinal venous saturation (SrvO2) was measured using an eye oximeter, and central venous saturation (SvO2) was measured using a fiber-optic catheter. After the shed blood was reinfused, the FiO2 was progressively decreased from 0.97 to 0.07. Femoral artery oxygen saturation (SaO2) and retinal artery oxygen saturation (SraO2) were measured at each increment.

RESULTS

During exsanguination, SrvO2 correlated with blood loss (r = -0.93) and SvO2 (r = 0.94). SraO2 correlated with SaO2 during incremental hypoxia (R2 = 0.93 +/- 0.15).

CONCLUSIONS

In this model of exsanguination, retinal venous oxygen saturation correlates with blood volume and with central venous oxygen saturation. The SraO2 correlates with SaO2 during graded hypoxia. Use of an eye oximeter to noninvasively monitor trauma patients appears promising and warrants further study.

Splenic control of intravascular volume in the rat

1. We tested the hypothesis that hypervolaemia causes an increase in intrasplenic filtration of cell-free fluid out of the vasculature. To this end we developed a preparation in the anaesthetized rat whereby the splenic vein could be non-occlusively cannulated. 2. Haematocrit and plasma protein concentrations were measured in the splenic afferent and efferent blood supplies. 3. In response to volume loading with saline (1% body weight), there was a sustained increase in the arterial-venous differential of haematocrit, i.e. there was a relative increase in the haematocrit of the blood draining from the spleen. There was no such change in plasma protein concentration. By contrast, this degree of volume loading had no effect on the haematocrit of blood passing through the hindquarters of the animal. 4. Following volume expansion, there was no significant difference in the protein concentration of the plasma and the lymph fluid collected from the splenic lymphatic duct. 5. Distension of the superior vena caval-right atrial junction by means of a small inflatable balloon, caused a similar increase in the splenic venous haematocrit, and again, no change in plasma protein concentration. 6. We interpret these results to mean that, in response to expansion of the intravascular space, there is increased intrasplenic filtration of plasma out of the blood and into the lymphatic system.

A microscopic investigation of the lymphoid organs of the beluga, Delphinapterus leucas

Lymphoid organs from belugas, Delphinapterus leucas, ranging in age from less than one to 16 years, were harvested during a sanctioned hunt to investigate morphology. The spleen is divisible into red and white pulp and a stroma consisting of a reticular network, a collagenous capsule, and trabeculae containing smooth muscle bundles. White pulp areas appear to be devoid of follicles and consist mainly of periarteriolar lymphatic sheaths (PALS), that are larger in younger than in older belugas. Definitive marginal zones between red and white pulp are difficult to discern in older belugas. Lymph nodes are similar to those of other mammals; they possess a follicular cortex surrounding a vascular medulla composed of lymphatic cords and sinuses. Smooth muscle is abundant in the medullary region, usually in close proximity to sinuses. The expansive nodular mass at the root of the mesentery, often referred to as the "pseudopancreas," is similar to lymph nodes in microscopic architecture. Pharyngeal tonsils and gut-associated lymphoid tissue (GALT) are found along the digestive tract and display an "active" morphology. Tonsils are comprised of lobules of follicles separated by vascular connective tissue. Epithelial-lined crypts communicate with the pharyngeal lumen. GALT consists of diffuse and follicular lymphocytes within the intestinal mucosa and submucosa. The thymus is well developed in the younger belugas, with lobules divisible into densely packed cortical zones of thymocytes and more loosely arranged medullary lymphocytes. Hassall's corpuscles are occasionally visible within the medulla. Cetaceans diverged evolutionarily from other mammals over 55 million years ago. This study investigates changes in lymphoid organ morphology in a species that now inhabits a unique ecological niche. This study also lays the groundwork for functional investigation of the beluga immune system, particularly as it relates to differences between healthy and stranded animals.

Characterization of angiotensin II receptor subtypes in the rat spleen

Quantitative autoradiography was used to determine the subtype of ANG receptors in the red pulp of the rat spleen. The AT1 antagonist DuP 753 competed for ANG binding with high affinity; binding was abolished by dithiothreitol. The AT2 competitor CGP 42112 A showed lower affinity, and the AT2 competitor PD 123177 did not affect binding at 10(-5) M. These data indicated the presence of only AT1 receptors. AT1 receptor number was similar in immature (2 weeks old) and adult (8 weeks old) rats. Binding was sensitive to guanine nucleotides, suggesting an association with G-proteins. Angiotensin II, at a dose of 10(-7) M, stimulated inositol phosphate formation 33% over control values in spleen from 8-week-old rats. This effect was significantly blocked by 10(-5) M DuP 753. We suggest a possible role of AT1 receptors in the regulation of splenic volume, blood flow, and lymphocyte function.

Size and hematological impact of the splenic erythrocyte reservoir in rainbow trout,Oncorhynchus mykiss

Fish were sampled individually, at rest, following air exposures of up to 8 min, during recovery from a 5 min air exposure or after a 5 minute chase. The spleen was photographedin vivo at rest and following 5 min air exposure in one fish. The effect of individual versus serial sampling from the same tank and of MS222 anaesthesia was also examined. Spleen hemoglobin content (SpHb), spleen somatic index (100 × spleen weight/body weight; SSI), blood hemoglobin concentration (Hb), and hematocrit (Ht), were measured. Mean cell hemoglobin concentration (MCHC), erythrocyte reservoir size, and relative contributions of reservoir release, erythrocyte swelling, and plasma water loss to hemoconcentration were calculated. The splenic reservoir contained 0.54 g Hb/kg body (21% of total body Hb), most of which it released between 1 and 3 minutes after the onset of air exposure. The spleen released more than 95% of the erythrocytes it contained at rest within 8 min. The release accounted for 31% of the 5.65 g/dl rise in Hb and 23% of the 26.6% observed increase in Ht after 8 minutes of air exposure. The balance of the increase was caused by erythrocyte swelling and fluid shifts reducing plasma volume. Animals exercised for 5 min showed changes similar to those in fish air exposed for 5 min. Recovery of all parameters was complete in 3 to 6 h, with the exception of MCHC which recovered in 30 min. Serial sampling produced a decrease in SpHb, and R1Wt and induced a significant hemoconcentration. MS222 did not cause erythrocyte release, but failed to prevent it after handling. Many previous reports of Ht and Hb in resting fish are probably high because they were taken under conditions that would cause the spleen to release its contents.

Histological, histochemical, and fine structural observations on the spleen of seals

Spleens of three species of Antarctic seals with different diving habits (Weddell seal, crabeater seal, and fur seal) have been studied with histological, histochemical, and electron microscopic methods. The spleens can be classified as nonsinusoidal, with capsule and trabeculae rich in innervated smooth muscle cells. The trabecular system is particularly well developed in the deep- and long-diving Weddell seal. As in other mammals the pulp can be divided into white and red pulp. In the white pulp, periarteriolar lymphatic sheaths and secondary lymphatic nodules occur; both are surrounded by a marginal zone rich in macrophages and eosinophils. The nodules can be observed frequently, which is in accordance with abundance of plasma cells in the red pulp. Well-developed white pulp and numerous plasma cells and eosinophils obviously reflect a high load of nematodes, which have mainly been found in lung and stomach. Additionally, in the red pulp morphological evidence for the following functions has been found: destruction of erythrocytes, erythropoiesis, and thrombopoiesis. In respect to blood flow through the red pulp, we interpret our observations in the following way: terminal branches of arterioles open into the space between the fibroblastic reticulum cells; blood draining from here is collected into pulp veins, which are mainly found near the trabeculae. Thus, the seals have an open vascular compartment in their spleens, as also occurs in the cat. The red pulp is innervated by numerous nerve fibers that seem to include both cholinergic and adrenergic ones. The target cells of these fibers seem to be the fibroblastic reticulum cells, whose state of contraction may influence the direction of blood flow through the red pulp.

Autoradiographic localization and characterization of angiotensin II binding sites in the spleen of rats and mice

Specific binding sites for angiotensin II (Ang II) were localized in the red pulp of the spleen of rats and mice by quantitative autoradiography using 125I-Sar1-Ang II as a ligand. In the rat, the binding was saturable and specific, and the rank order for Ang II derivatives as competitors of 125I-Sar1-Ang II binding correlates well with their affinity for Ang II receptors in other tissues. Kinetic analysis in the rat spleen revealed a single class of binding sites with a KD of 1.11 nM and a Bmax value of 81.6 fmol/mg protein. Ang II binding sites were also localized on isolated rat spleen cells with similar affinity but with much lower Bmax, 9.75 fmol/mg protein. Ang II receptors were not detected in thymus sections from rats or mice, or on isolated rat thymocytes. The binding sites described here might represent a functional Ang II receptor with a role in the regulation of splenic volume and blood flow and in the modulation of the lymphocyte function.

Mechanisms of splenic control of murine malaria: reticular cell activation and the development of a blood-spleen barrier

By complex stromal responses, the spleen controls the course of nonlethal Plasmodium yoelii murine malaria. The course of disease may be divided into four phases. In the immediate postinfective phase, lasting several days, the filtration beds of the spleen are open. Parasitized and nonparasitized erythrocytes, many plasma cells, lymphocytes, and macrophages are sequestered from the blood; and most or all of the parasitized erythrocytes are phagocytized. In the following precrisis phase, approximately 1 week long, there is increasing parasitemia and anemia. The filtration beds of the spleen support large-scale erythropoiesis, lymphopoiesis, plasmacytopoiesis, and monocyte-to-macrophage differentiation. Reticular cells, the stromal cells which form the splenic filtration beds, become activated, showing signs of intense protein secretion and increased branching and mitosis. The locules of the filtration beds appear sealed off from the blood by branches of activated reticular cells. A blood-spleen barrier is thereby formed, protecting splenic hematopoiesis from the parasite. Factors are produced, moreover, which damage intraerythrocytic parasites, producing crisis forms. Crisis follows. It may occur over several days, presaged by the appearance of circulating crisis forms. The filtration beds are opened to the blood. Circulating crisis forms are trapped within the locules of the filtration beds and phagocytized while the stores of reticulocytes produced there in the precrisis period are released to the blood. The malaria, as a result, is no longer patent and the anemia is relieved. In the fourth or postcrisis phase, lasting many months, the normal structure of the spleen is approached. We postulate that reticular cells, normal and activated, have the following functions: to fabricate the locules of the filtration beds; to control the migration of free cells through these beds; to trap free cells, including parasitized erythrocytes, by cell-surface adherence; to open or close the filtration locules, creating a dynamic blood-spleen barrier; to control the circulation of the spleen--by contraction and alignment in normal spleens and by activation and closing of locules in enlarged spleens; to synthesize collagen III; to synthesize factors which influence marrow release of monocytes; and to secrete antiplasmodial substances.